CS 25.1411 General

ED Decision 2008/006/R

(a) Accessibility. Required safety equipment to be used by the crew in an emergency must be readily accessible.

(b) Stowage provisions. Stowage provisions for required emergency equipment must be furnished and must –

(1) Be arranged so that the equipment is directly accessible and its location is obvious; and

(2) Protect the safety equipment from inadvertent damage.

(c) Emergency exit descent device. The stowage provisions for the emergency exit descent device required by CS 25.810(a) must be at the exits for which they are intended.

(d) Liferafts

(1) The stowage provisions for the liferafts described in CS 25.1415 must accommodate enough rafts for the maximum number of occupants for which certification for ditching is requested.

(2) Life rafts must be stowed near exits through which the rafts can be launched during an unplanned ditching.

(3) Rafts automatically or remotely released outside the aeroplane must be attached to the aeroplane by means of the static line prescribed in CS 25.1415.

(4) The stowage provisions for each portable life raft must allow rapid detachment and removal of the raft for use at other than the intended exits.

(e) Long-range signalling device. The stowage provisions for the long-range signalling device required by CS 25.1415 must be near an exit available during an unplanned ditching.

(f) Life-preserver stowage provisions. The stowage provisions for life preservers described in CS 25.1415 must accommodate one life preserver for each occupant for which certification for ditching is requested. Each life preserver must be within easy reach of each seated occupant.

(g) Life line stowage provisions. If certification for ditching under CS 25.801 is requested, there must be provisions to store the lifelines. These provisions must –

(1) Allow one life line to be attached to each side of the fuselage; and

(2) Be arranged to allow the lifelines to be used to enable the occupants to stay on the wing after ditching. This requirement is not applicable to aeroplanes having no over-wing ditching exits.

[Amdt 25/5]

AMC 25.1411(f) Life preserver stowage provisions

ED Decision 2020/024/R

The applicant should demonstrate that the life preserver is within easy reach of, and can be readily removed by, a seated and belted occupant (shoulder strap(s) may be removed prior to the demonstration), for all seat orientations and installations that are intended for use during taxi, take‑off and landing. In lieu of an actual life preserver, a representative object (e.g. of the same size and weight) may be utilised for testing. The evaluation to quickly retrieve the preserver is to begin with the occupant moving their hand(s) from the seated position to reach for the preserver and to end with the occupant having the preserver in their hand(s) and fully removed from the stowage container. It does not include the time for the occupant to return to the upright position, to remove a pull strap from the preserver (if used) or to open the preserver package provided by the preserver manufacturer.

The applicant should test the critical configuration(s) to demonstrate retrieval of the life preserver in less than 10 seconds by a minimum of 5 test subjects with a success rate of no less than 75 %. The test should evaluate three anticipated occupant test subject size categories: the 5th, 50th and 95th percentile. At least one occupant from each size category should demonstrate successful retrieval within 10 seconds. No more than 40 % of the overall test subject population should be in the 5th or 95th percentile occupant categories.

1) For passenger seats, the test subjects should be naïve. For the purpose of this test, naïve test subjects should be defined as follows: they should have had no experience within the prior 24 months in retrieving a life preserver. The subjects should receive no retrieval information other than a typical preflight briefing. The occupant size categories to be evaluated should be defined as:

a. A 5th percentile occupant is no taller than 1.5 m (60 in).

b. A 50th percentile occupant is at least 1.6 m (63 in) tall but no taller than 1.8 m (70 in).

c. A 95th percentile occupant weighs at least 110.7 kg (244 lb).

2) For flight attendant and observer seats, the test subjects do not need to be naïve. The occupant size categories to be evaluated should be defined as:

a. A 5th percentile occupant is no taller than 1.5 m (60 in).

b. A 50th percentile occupant is at least 1.6 m (63 in) tall but no taller than 1.8 m (70 in).

c. A 95th percentile occupant weighs at least 110.7 kg (244 lb).

3) For pilot/co-pilot seats, the test subjects do not need to be naïve. The occupant size categories to be evaluated should be defined as:

a. A 5th percentile occupant is no taller than 1.57 m (62 in).

b. A 50th percentile occupant is at least 1.6 m (63 in) tall but no taller than 1.8 m (70 in).

c. A 95th percentile occupant weighs at least 110.7 kg (244 lb).

[Amdt 25/26]

CS 25.1415 Ditching equipment

ED Decision 2003/2/RM

(a) Ditching equipment used in aeroplanes to be certified for ditching under CS 25.801, and required by the Operating Rules, must meet the requirements of this paragraph.

(b) Each liferaft and each life preserver must be approved. In addition –

(1) Unless excess rafts of enough capacity are provided, the buoyancy and seating capacity beyond the rated capacity of the rafts must accommodate all occupants of the aeroplane in the event of a loss of one raft of the largest rated capacity; and

(2) Each raft must have a trailing line, and must have a static line designed to hold the raft near the aeroplane but to release it if the aeroplane becomes totally submerged.

(c) Approved survival equipment must be attached to, or stored adjacent to, each liferaft.

(d) There must be an approved survival type emergency locator transmitter for use in one life raft.

(e) For aeroplanes, not certificated for ditching under CS 25.801 and not having approved life preservers, there must be an approved flotation means for each occupant. This means must be within easy reach of each seated occupant and must be readily removable from the aeroplane.

CS 25.1419 Ice Protection

ED Decision 2009/013/R

(See AMC 25.1419)

If the applicant seeks certification for flight in icing conditions, the aeroplane must be able to safely operate in the continuous maximum and intermittent maximum icing conditions of Appendix C. To establish this–

(a) An analysis must be performed to establish that the ice protection for the various components of the aeroplane is adequate, taking into account the various aeroplane operational configurations; and

(b) To verify the ice protection analysis, to check for icing anomalies, and to demonstrate that the ice protection system and its components are effective, the aeroplane or its components must be flight tested in the various operational configurations, in measured natural atmospheric icing conditions, and as found necessary, by one or more of the following means:

(1) Laboratory dry air or simulated icing tests, or a combination of both, of the components or models of the components.

(2) Flight dry air tests of the ice protection system as a whole, or of its individual components.

(3) Flight tests of the aeroplane or its components in measured simulated icing conditions.

(c) Caution information, such as an amber caution light or equivalent, must be provided to alert the flight crew when the anti-ice or de-ice system is not functioning normally.

(d) For turbine engine powered aeroplanes, the ice protection provisions of this paragraph are considered to be applicable primarily to the airframe. For the powerplant installation, certain additional provisions of Subpart E may be found applicable.

(e)  One of the following methods of icing detection and activation of the airframe ice protection system must be provided:

(1)  A primary ice detection system that automatically activates or alerts the flight crew to activate the airframe ice protection system; or

(2)  A definition of visual cues for recognition of the first sign of ice accretion on a specified surface combined with an advisory ice detection system that alerts the flight crew to activate the airframe ice protection system; or

(3)  Identification of conditions conducive to airframe icing as defined by an appropriate static or total air temperature and visible moisture for use by the flight crew to activate the airframe ice protection system.

(f)  Unless the applicant shows that the airframe ice protection system need not be operated during specific phases of flight, the requirements of paragraph (e) of this section are applicable to all phases of flight.

(g)  After the initial activation of the airframe ice protection system:

(1)  The ice protection system must be designed to operate continuously; or

(2)  The aeroplane must be equipped with a system that automatically cycles the ice protection system; or

(3)  An ice detection system must be provided to alert the flight crew each time the ice protection system must be cycled.

(h)  Procedures for operation of the ice protection system, including activation and deactivation, must be established and documented in the Aeroplane Flight Manual.

[Amdt 25/3]

[Amdt 25/7]

AMC 25.1419 Ice Protection

ED Decision 2015/008/R

If certification for flight in icing conditions is desired, the aeroplane must be able to safely operate throughout the icing envelope defined in Appendix C.

In the context of this AMC, the wording “relevant icing environment” means the Appendix C icing conditions.

CS 25.1419 provides specific airframe requirements for certification for flight in the icing conditions defined in Appendix C. Additionally, for other parts of the aeroplane (i.e., engine, engine inlet, propeller, flight instrument external probes, windshield) there are more specific icing related CS-25 specifications and associated acceptable means of compliance.

Other icing related specifications must be complied with, even if the aeroplane is not certificated for flight in icing:

CS 25.629(d)(3)

CS 25.975(a)(1)

CS 25.1093(b)

CS 25.1324

CS 25.1325(b)

CS 25.1326

CS 25J1093(b)

Additional information for showing compliance with the aeroplane performance and handling qualities requirements for icing certification may be found in AMC 25.21(g)

(a)  CS 25.1419(a) Analysis

The applicant should prepare analysis to substantiate the choice of ice protection equipment for the aeroplane. Such analysis should clearly state the basic protection required and the assumptions made, and delineate methods of analysis used. All analysis tools and methods should be validated by tests or should have been validated by the applicant on a previous certification program. The applicant who uses a previously validated method should substantiate why that method is applicable to the new program.

1.  Analytical Simulation Methods

Analytical simulation methods for icing include impingement and accretion models based on computational fluid dynamics. The applicant will typically use these methods to evaluate protected as well as unprotected areas for potential ice accretions. Analytical simulation provides a way to account for the variability in drop distributions. It also makes it possible to examine impingement in relation to visual icing cues and to analyse the location of detection devices for detrimental local flow effects.

2.  Analysis of areas and components to be protected

In evaluating the aeroplane’s ability to operate safely in the relevant icing environment, and in determining which components will be protected, the applicant should examine relevant areas to determine the degree of protection required. An applicant may determine that protection is not required for one or more of these areas or components. If so, the applicant’s analysis should include the supporting data and rationale for allowing those areas or components to remain unprotected.

The applicant should show that:

             the lack of protection does not adversely affect handling characteristics or performance of the aeroplane, as required by CS 25.21(g),

             the lack of protection does not cause unacceptable affects upon the operation and functioning of affected systems and equipment,

             the lack of protection does not affect the flight instrument external probes systems, and

             shedding of ice accreting on unprotected areas will not create unacceptable damages to the engines or the surrounding components which would prevent continued safe flight and landing.

3.  Impingement Limit Analysis

The applicant should prepare a drop trajectory and impingement analysis of:

             wings,

             horizontal and vertical stabilizers,

             engine air intakes,

             propellers,

             any means used to detect ice accretion (ice detector, visual cues) and

             all other critical surfaces upon which ice may accrete.

This analysis should consider the various aeroplane operational configurations, phases of flight, and associated angles of attack.

The impingement limit analysis should establish upper and lower aft drop impingement limits that can then be used to establish the aft ice formation limit and its relationship to the Ice Protection Systems (IPS) coverage.

Water content versus drop size relationships defined in Appendix C, Figures 1 and 4 are defined in terms of mean effective drop diameter. CS-25 does not require consideration of specific distributions for Appendix C icing conditions.

In determining the rates of catch, the full spectrum of the droplet sizes should be considered but in determining impingement areas, a maximum droplet size of 50 μm need only be considered for compliance to CS 25.1419.

4.  Ice Shedding Analysis

For critical ice shedding surfaces an analysis must be performed to show that ice shed from these surfaces will not create unacceptable damages which would prevent continued safe flight and landing.

Airframe ice shedding may damage or erode engine or powerplant components as well as lifting, stabilizing, and flight control surface leading edges. Fan and compressor blades, impeller vanes, inlet screens and ducts, and propellers are examples of powerplant components subject to damage from shedding ice. For fuselage-mounted turbojet engines (and pusher propellers that are very close to the fuselage and well aft of the aeroplane's nose), ice shedding from the forward fuselage and from the wings may cause significant damage. Ice shedding from components of the aeroplane, including antennas, should not cause damage to engines and propellers that would adversely affect engine operation or cause an unacceptable loss of power or thrust (compliance with CS 25.1093(b)).

The applicant should also consider aeroplane damage that can be caused by ice shedding from the propellers.

Control surfaces such as elevators, ailerons, flaps, and spoilers, especially those constructed of thin metallic, non-metallic, or composite materials, are also subject to damage.

Currently available trajectory and impingement analysis may not adequately predict such damage. Unpredictable ice shedding paths from forward areas such as radomes and forward wings (canards) have been found to negate the results of these analysis.

For this reason, a damage analysis should consider that the most critical ice shapes will shed and impact the areas of concern.

5.  Thermal Analysis and Runback Ice

An analysis shall be performed to predict the effectiveness of the thermal IPS (hot air or electrical). Design objectives (fully evaporative or running wet) shall be assessed against the relevant icing environment.

Water not evaporated by thermal ice protection systems and unfrozen water in near-freezing conditions (or in conditions when the freezing fraction is less than one) may run aft and form runback ice. This runback ice can then accumulate additional mass from direct impingement.

Runback ice should be determined and should be considered when determining critical ice shapes. Simulated runback ice shapes may be used when evaluating effects of critical ice shapes. Computer codes may be unable to estimate the characteristics of the runback water or resultant ice shapes (rivulets or thin layers), but some codes may be able to estimate the mass of the runback ice. Thus runback ice should be determined experimentally, or the mass determined by computer codes with assumptions about runback extent and thickness similar to those used successfully with prior models.

The applicant should consider potential hazards resulting from the shedding of runback ice.

6.  Power Sources

The applicant should evaluate the power sources in the IPS design (e.g. electrical, bleed air, or pneumatic sources). An electrical load analysis or test should be conducted on each power source to determine that it is adequate to operate the IPS as well as to supply all other essential electrical loads for the aeroplane throughout the aeroplane flight envelope. The effect of an IPS component failure on availability of power to other essential loads should be evaluated in accordance with CS 25.1309. All power sources affecting engines or engine IPS for multiengine aeroplanes must comply with the engine isolation requirements of CS 25.903(b).

7.  Artificial ice shapes and roughness

AMC 25.21(g) contains guidance on icing exposure during various phases of flight that should be considered when determining artificial ice shapes and surface roughness. The shape and surface roughness of the ice should be developed and substantiated with acceptable methods. When developing critical ice shapes, the applicant should consider ice accretions that will form during all phases of flight and those that will occur before activation and proper functioning of the ice protection system.

If applicable, runback, residual, and inter-cycle ice accretions should also be considered.

The applicant should substantiate the drop diameter (mean effective, median volume), liquid water content, and temperature that will cause formation of an ice shape critical to the aeroplane’s performance and handling qualities.

Ice roughness used should be based on icing tunnel, natural icing, or tanker testing, or the guidance in AMC 25.21(g), Appendix 2.

8.  Similarity Analysis

(i)  For certification based on similarity to other type-certificated aeroplanes previously approved for flight in icing conditions, the applicant should specify the aeroplane model and the component to which the reference of similarity applies. The applicant should show specific similarities in the areas of physical, functional, thermodynamic, ice protection system, and aerodynamic characteristics as well as in environmental exposure. The applicant should conduct analysis to show that component installation, operation, and effect on the aeroplane’s performance and handling are equivalent to that of the same or similar component in the previously approved configuration.

(ii)  A demonstration of similarity requires an evaluation of both system and installation differences. Differences should be evaluated for their effect on IPS functionality and on safe flight in icing. If there is uncertainty about the effects of the differences, the applicant should conduct additional tests and/or analysis as necessary and appropriate to resolve the open issues.

(iii)  CS 25.1419(b) requires flight testing in measured natural icing conditions. Flight test data from previous certification programs may be used to show compliance with CS 25.1419(b) if the applicant can show that the data is applicable to the aeroplane in question. If there is uncertainty about the similarity analysis, the applicant should conduct flight tests in measured natural icing conditions for compliance with CS 25.1419(b).

Note: The applicant must possess all the data to substantiate compliance with applicable specifications, including data from past certifications upon which the similarity analysis is based.

(b)  CS 25.1419(b) Testing

The aeroplane should be shown to comply with certification specifications when all IPS are installed and functioning when operating normally and under certain failure conditions. This can normally be accomplished by performing tests in natural or simulated icing conditions to either validate analysis or to test those conditions found to be most critical to basic aeroplane aerodynamics, IPS design, and powerplant functions. All IPS equipment should perform their intended functions throughout the entire operating envelope.

The primary purposes of flight testing are to:

             Determine that the IPS is acceptably effective and performs its intended functions during flight as predicted by analysis or ground testing,

             Evaluate any degradation in performance and flying qualities,

             Verify the adequacy of flightcrew procedures as well as limitations for the use of the IPS in normal, abnormal, and emergency conditions,

             Confirm that the powerplant installation as a whole (engine, propeller, inlet, anti-ice system, etc.) performs satisfactorily in icing conditions, and

             Validate the ice accretion size, location, texture and other general characteristics.

Performance and handling qualities specifications are identified in CS 25.21(g). Flight tests to show compliance with these requirements are addressed in AMC 25.21(g).

1.  Dry air flight tests with ice protection equipment operating

The first flight tests conducted to evaluate the aeroplane with the IPS operating are usually dry air flight tests. The initial dry air tests are conducted to:

             Verify that the IPS does not affect flying qualities of the aeroplane in clear air, and

             Obtain a thermal profile of an operating thermal IPS to substantiate its thermal performance.

Several commonly used IPS and components are discussed below to illustrate typical dry air flight test practices. Other types of equipment should be evaluated as their specific design dictates.

1.1  Thermal ice protection leading edge systems

Dry air flight tests are conducted to verify the system design parameters and thermal performance analysis.

Normally, instruments are installed on system components to measure the anti-icing mass flow rate or energy input (for electrical systems), supply air temperature, and surface temperatures. The dry air test plan generally includes operating conditions such as the climb, holding, and descent phases of a normal flight profile. Since the presence of moisture can affect surface temperatures, tests should be conducted where no visible moisture is present.

Measurements of supply air mass flow rate, energy input, and air temperature allow determination of how much heat is available to the system. The adequacy of the IPS can then be demonstrated by comparing the measured data to the theoretical analysis.

Surface temperatures measured in the dry air, for example, can be useful in extrapolating the maximum possible leading edge surface temperature in-flight, the heat transfer characteristics of the system, and the thermal energy available for the IPS. Supply air temperatures or energy input may also be used to verify that the IPS materials were appropriately chosen for the thermal environment.

1.2  Bleed air systems

Effects of bleed air extraction on engine and aeroplane performance, if any, should be examined and included in the Aeroplane Flight Manual (AFM) performance data. The surface heat distribution analysis should be verified for varying flight conditions including climb, cruise, hold, and descent. Temperature measurements may be necessary to verify the thermal analysis. In accordance with provisions of CS 25.939(a), the maximum bleed air for ice protection should have no detrimental effect on engine operation throughout the engine’s power range.

1.3  Pneumatic leading edge boots

Tests should demonstrate a rise and decrease in operating pressures, which results in the effective removal of ice. This pressure rise time, as well as the maximum operating pressure for each boot, should be evaluated throughout the altitude range defined in the relevant icing environment. The appropriate speed and temperature limitation (if any) on boot activation should be included in the AFM. Boot inflation should have no significant effect on aeroplane performance and handling qualities.

1.4  Fluid anti-icing/de-icing systems

Flight testing should include evaluation of fluid flow paths to confirm that adequate and uniform fluid distribution over the protected surfaces is achieved. A means of indicating fluid flow rates, fluid quantity remaining, etc., should be evaluated to determine that the indicators are plainly visible to the pilot and that the indications provided can be effectively read. The AFM should include information advising the flight crew how long it will take to deplete the amount of fluid remaining in the reservoir.

2.  Dry air flight tests with predicted artificial ice shapes and roughness

The primary function of dry air flight tests with artificial ice shapes is to demonstrate the ability of the aeroplane to operate safely with an accumulation of critical ice shapes based on exposure to icing conditions. The specific flight tests used to evaluate aeroplane performance and handling qualities are addressed in AMC 25.21(g).

For failure conditions of the IPS that are not extremely improbable, validation testing may be required to demonstrate that the effect on safety of flight (as measured by degradation in flight characteristics) is commensurate with the failure probability. The applicant may use dry air flight tests with predicted critical failed IPS ice shapes, which may include asymmetric ice shapes, to demonstrate acceptable operational safety.

3.  Icing flight tests

Flight tests in measured natural icing and tests performed with artificial icing tools, such as icing tankers, are normally used to demonstrate that the IPS performs during flight as predicted by analysis or other testing. Such tests are also used to confirm analysis used in developing the various components, such as ice detectors, and ice shapes. CS 25.1419 requires measured natural icing flight tests within the icing conditions of CS-25, Appendix C. The natural icing flight tests are accomplished to corroborate the general nature of the effects on aeroplane handling characteristics and performance determined with artificial ice shapes (see AMC 25.21(g)), as well as to qualitatively assess the analytically predicted location and general physical characteristics of the ice accretions. If necessary, there should be a means to record ice accumulations to allow the size, location, shape, extent and general nature of the ice to be approximated. Various means can be used to aid this, such as a rod or fence mounted on the aerofoil and black or brightly coloured paint on the aerofoil to increase the contrast between the ice accretion and the aerofoil and aid the determination of the ice shape size.

3.1  Instrumentation

The applicant should plan sufficient instrumentation to allow documentation of important aeroplane, system, and component parameters, as well as icing conditions encountered. The following parameters should be considered:

1.  Altitude.

2.  Airspeed.

3.  Engine power level or speed.

4.  Propeller speed and pitch, if applicable.

5.  Temperatures that could be affected by ice protection equipment or ice accumulation or that are necessary for validation of analysis, such as the temperatures of Static air, Engine components, Electrical generation equipment, Surfaces, Structural components.

6.  Liquid water content. This should be measured over the complete water drop size distribution.

7.  Median volume drop diameter and drop diameter spectra. When measurement of the icing environment drop diameter is necessary, instrumentation used for measuring drop sizes should be appropriate for the icing environment considered.

3.2  Artificial icing

Flight testing in artificial icing environments, such as behind icing tankers, is one way to predict capabilities of individual elements of the ice protection equipment and to determine local ice shapes.

Since the ice plume has a limited cross-section, testing is usually limited to components, such as heated pitot tubes, antennas, air inlets including engine induction air inlets, empennage, aerofoil sections, and windshields. Calibration and verification of the icing cloud produced by the tanker should be accomplished as necessary for meeting test objectives.

Use of an icing tanker can provide high confidence in local icing effects. But obtaining small drop sizes may be difficult with some spray nozzles. As a result, these methods could produce larger ice build-ups and different ice shapes than those observed in natural Appendix C icing conditions.

Icing tanker techniques can be used in a manner similar to icing tunnel testing with respect to ice shape development. The plume may be of sufficient size that it could be applied to sections of the airframe to examine any potential hinge moment or CLmax (maximum lift coefficient) effects from ice accretions behind protected areas.

This method also has the advantage of being able to combine the effects of thermal systems (such as runback) with direct accretion to simulate resulting ice accumulations.

Atmospheric effects such as humidity and drop residence time (time required to bring the drop to static temperature) should be considered in this type of testing.

3.3  Appendix C natural icing flight testing

CS 25.1419(b) requires measured natural icing flight tests. Flight tests in measured natural icing conditions are intended to verify the ice protection analysis, to check for icing anomalies, and to demonstrate that the IPS and its components function as intended.

The aeroplane should be given sufficient exposure to icing conditions to allow extrapolation to the envelope critical conditions by analysis. Test data obtained during these exposures may be used to validate the analytical methods used and the results of any preceding artificial icing tests.

Flight testing in natural icing conditions should also be used to verify AFM procedures for activation of the IPS, including recognition and delay times associated with IPS activation. Such testing should verify the analytically predicted location and general physical characteristics of the ice accretions. Critical ice accumulations should be observed, where possible, and sufficient data taken to allow correlation with dry air testing. Remotely located cameras either on the test aeroplane or on a chase aeroplane have been used to document ice accumulations on areas that cannot be seen from the test aeroplane’s flight deck or cabin.

For an aeroplane with a thermal de-icing system, the applicant should demonstrate the effectiveness of the de-icing operation either in artificial icing conditions or during a natural icing flight test certification program. The tests usually encompass measurements of the surface temperature time history. This time history includes the time at which the system is activated, the time at which the surface reaches an effective temperature, and the time at which the majority of ice is shed from the leading edge. Any residual or intercycle ice accretions should be documented. The data should be recorded in the flight test report.

For anti-icing/de-icing fluid systems, fluid flow paths should be determined when the fluid is mixed with impinging water during system operation.

4.  Icing wind tunnel tests

Icing wind tunnels provide the ability to simulate natural icing conditions in a controlled environment. Scale models may be used with appropriate scaling corrections, if the scale testing on the component has been validated with full-scale testing or analysis. Hybrid models, with the full-scale leading edge extending beyond the impingement limits, may also be used. The applicant may use these models to estimate impingement limits, examine visual icing cues, and evaluate ice detection devices.

A variety of icing conditions can be simulated, depending on the icing wind tunnel.

Icing wind tunnels have been used to evaluate ice shapes on unprotected areas and on or aft of protected areas, such as inter-cycle, residual, and runback ice. They have also been used to evaluate performance of IPS, such as pneumatic and thermal systems.

For the evaluation of the performance of the IPS, a critical points analysis can be used to identify critical test conditions under which an IPS should be tested in an icing tunnel. In lieu of a critical points analysis the following conditions have been successfully used in the past to simulate the Appendix C conditions:

4.1  Continuous Maximum Condition

Atmospheric Temperature (oC)

Liquid Water Content (g/m3)

0

0.8

-10

0.6

-20

0.3

-30

0.2

The test should be run until steady state conditions are reached. The steady state can be identified by the protected surfaces being completely free of ice or the total ice accretion being contained by repetitive shedding either naturally or enforced by cyclic operation of the IPS. If the steady state cannot be reached, the duration of the run should be limited to 45 minutes.

4.2  Intermittent Maximum Conditions

The encounters considered should include three clouds of 5 km horizontal extent with Intermittent Maximum concentrations as in the following table separated by spaces of clear air of 5 km.

Atmospheric Temperature (oC)

Liquid Water Content (g/m3)

0

2.5

-10

2.2

-20

1.7

-30

1.0

For both the Continuous maximum and Intermittent Conditions, an MVD of 20 µm should be used.

5.  Dry air wind tunnel tests

Dry air wind tunnel testing using scaled models and artificial ice shapes has been used to determine if ice protection on particular components (horizontal/vertical plane or wing sections) is required. The scaling, including the effect of the roughness of the ice, should be substantiated using methods found acceptable to the Agency.

(c)  CS 25.1419(c) Caution information

CS 25.1419(c) requires that Caution information be provided to alert the flight crew when the IPS is not functioning normally. In this context, Caution information is considered to be a general term referring to an alert rather than referring specifically to a Caution level alert. Crew alerting should be provided for failure conditions of the IPS in accordance with CS 25.1309(c) and CS 25.1322. It should be assumed that icing conditions exist during the failure event. In accordance with CS 25.1419(c), the decision to provide an alert must not be based on the numerical probability of the failure event. However, the type of alert provided should be based on the failure effects and necessary crew action to be performed in response.

1) Sensor(s) used to identify a failure condition should be evaluated to ensure that they are properly located to obtain accurate data on the failure of the IPS.

2) The indication system should not be designed so that it could give the flight crew a false indication that the system is functioning normally because of a lack of an alert. The applicant should submit data to substantiate that this could not happen. For example, if a pneumatic de-icing system (boots) requires a specific minimum pressure and pressure rise rate to adequately shed ice, an alert should be provided if that minimum pressure and pressure rise rate are not attained. Without an alert, the flight crew may erroneously believe that the boots are operating normally when, in fact, they might not be inflating with sufficient pressure or with a sufficient inflation rate to adequately shed ice. The applicant should also consider the need for an alert about ice forming in the pneumatic system that can result in low pneumatic boot pressures or an inadequate pressure rise rate.

(d)  CS 25.1419(e) Ice Detection

1.  Compliance with CS 25.1419(e)(1) and (e)(2).

These subparagraphs provide alternatives to CS 25.1419(e)(3) which specifies operation of the IPS based on icing conditions . These alternatives require either a primary ice detection system, or substantiated visual cues and an advisory ice detection system. CS 25.1419(e)(2) requires defined visual cues for recognition of the first sign of ice accretion on a specified surface combined with an advisory ice detection system that alerts the flight crew to activate the airframe ice protection system. The following conditions should be considered when determining compliance with CS 25.1419(e)(2):

             The advisory ice detection system annunciates when icing conditions exist or when the substantiated visual cues are present.

             The defined visual cues rely on the flight crew’s observation of the first sign of ice accretion on the aeroplane and do not depend on the pilot determining the thickness of the accretion.

             The flight crew activates the ice protection system when they observe ice accretion or when the ice detector annunciates ice, whichever occurs first.

1.1  Ice detection system (IDS)

1.1.1  Primary Ice Detection System (PIDS)

A PIDS must either alert the flight crew to operate the IPS using AFM procedures or automatically activate the IPS before an unsafe accumulation of ice on the airframe, engine components, or engine air inlets occurs. The primary ice detection system must perform its intended function for the aeroplane configurations, phases of flight, and within the relevant icing environment.

1.1.2  Advisory Ice Detection System (AIDS)

The AIDS, in conjunction with visual cues, such as visible ice accretion on referenced or monitored surfaces, should advise the flight crew to initiate operation of the IPS using AFM procedures. An AIDS is not the prime means used to determine if the IPS should be activated. When there is an AIDS installed on an aeroplane, the flight crew has primary responsibility for determining when the IPS must be activated; an AIDS that would automatically activate the IPS(s) would not be accepted. Although the flight crew has primary responsibility for determining when the IPS must be activated, if the aeroplane is certificated in accordance with CS 25.1419(e)(2), the AIDS is required (i.e. not optional) and must perform its intended function for the aeroplane configurations, for its phases of flight, and within the relevant icing environment.

1.1.3  Performance and Installation of the ice detection system (IDS)

(i)  An IDS should be capable of detecting the presence of icing conditions or actual ice accretion under all atmospheric conditions defined in the relevant icing environment.

It should be demonstrated that the presence of ice crystals mixed with supercooled liquid water does not lead to unacceptable supercooled liquid water ice detection performance degradation, when assessed at aircraft level.

For IDS capable of detecting the presence of ice on a monitored surface, the IDS should always detect when ice is present on the monitored surface whether or not icing conditions are within the relevant icing environment and the IDS should not indicate the presence of ice when no ice is present.

(ii)  The applicant should accomplish a drop impingement analysis and/or tests to ensure that the ice detector(s) are properly located. The ice detector should be located on the airframe surface where the sensor is adequately exposed to the icing environment. The applicant should conduct flow field and boundary-layer analysis of candidate installation positions to ensure that the ice detector sensor is not shielded from impinging water drops. The IDS should be shown to operate in the range of conditions defined by the icing environment. Performance of the IDS is affected by the physical installation and can only be verified after installation. It should be shown by analysis and/or flight test that the location(s) of the detection systems sensor(s) is adequate to cover all aeroplane operational configurations, phases of flight, airspeeds, associated angles of attack and sideslip.

A combination of tests and analysis is required to demonstrate performance of the ice detector as installed on the aeroplane. This could include icing tunnel and icing tanker tests to evaluate ice detector performance. The applicant may use drop impingement analysis to determine that the ice detector functions properly over the drop range of the icing environment when validated through natural or artificial icing tests (e.g. tanker, icing tunnel). The applicant should demonstrate that the aeroplane can be safely operated with the ice accretions formed up to the time the ice protection system becomes effective, following activation by the ice detector. The detector and its installation should minimize nuisance warnings.

(iii)  Evidences should be provided that the system is qualified under the appropriate standards, and in addition, it should be demonstrated that when installed on the aeroplane the IDS can detect under:

             Light icing conditions (minimum detectability),

             Heavy glaze ice conditions (warm runback), and

             Cold, high-LWC (Liquid Water Content) conditions (thermal load).

(iv)  The maximum detection threshold should be established. The threshold level chosen to activate the ice detection and annunciation system should be guided by the assurance that:

             The aeroplane has adequate controllability and stall warning margins with the ice accretions that exist on the unprotected and protected surfaces prior to normal activation of the IPS(s);

             The amount of ice accreted can be safely eliminated by the IPS(s). It should be demonstrated that when the amount of ice that is accreted on the protected surfaces is shed, no unacceptable damages occur to the airframe or the engines;

             The system will not be overly sensitive, but sensitive enough to readily detect sudden exposure; and

             If the thickness of accreted ice is in excess of the maximum detection threshold on the monitored surface, the IDS should continue to indicate the presence of ice.

(v)  If the IDS ice detection logic is inhibited during certain flight phases, handling qualities and performance should be demonstrated, assuming that the ice protection systems are inoperative and the aeroplane is operating in conditions conducive to icing.

(vi)  If an accretion-based technology is used for ice detection, and if the IDS cannot detect ice in some condition where ice accretes on critical aircraft surfaces:

             For PIDS, the applicant should either show that the aeroplane can be operated safely with the ice accretions, or the IPS(s) should be forced to operate within the envelope of non-detection of the PIDS.

             For AIDS, if such icing conditions may go undetected by the flight crew (absence of visual cues for these conditions), then the IPS(s) should be forced manually to operate within the envelope of non-detection of the AIDS.

 Alternatively, the installation of an icing conditions detector (i.e. one that detects both moisture and temperature), or additional substantiation with the resulting undetected ice accretions, may be required.

(vii)  Preferably, the IDS should be turned on automatically at aeroplane power-up, and an alert should be provided if the IDS is turned off.

(viii)  If the PIDS has automatic control of the IPS(s), it should be possible to de-select the automatic feature and to revert to an advisory system.

(ix)  During the certification exercise, the proper operation of the IDS should be monitored especially by comparison with other icing signs (visual cues, ice accretion probe, etc.). Cloud conditions of the icing encounter should be measured and recorded. When multiple ice detectors are used in an IDS, signals from each ice detector should be recorded during icing tests to verify whether the ice detectors are fully redundant in the whole Appendix C and flight envelope or rather have their own detection threshold to cover the whole Appendix C and flight envelope.

1.1.4  Aeroplane Flight Manual (AFM)

AFM procedures have to be established to cover system malfunction and actions to be taken by the flight crew when alerted by the system. The AFM should at least address the following:

             Pre-flight check, if required, to verify the correct functioning of the IDS,

             Operational use of the IDS and limitations, and

             Appropriate flight crew procedure(s) in case of failure indication(s).

1.1.5  Ice detection system safety considerations

The applicant should accomplish a functional hazard assessment to determine the hazard level associated with failure of the ice detection system (refer to AMC 25.1309).

The probability of encountering the icing conditions defined in Appendix C to CS-25 should be considered to be 1.

The un-annunciated failure of a PIDS is assumed to be a catastrophic failure condition, unless characteristics of the aeroplane in icing conditions without activation of the aircraft IPS(s) are demonstrated to result in a less severe hazard category. When showing compliance to CS 25.1309 and when considering PIDS integrating multiple ice detectors, it should be assumed that the loss of one ice detector leads to the loss of the primary ice detection function, unless it is demonstrated during flight tests that all ice detectors have comparable ice detection performance. After the loss of one ice detector, the applicant may choose to revert to an advisory ice detection system; in this case the applicant should substantiate visual cues and AFM procedures in compliance with CS 25.1419(e)(2).

If visual cues are the primary means of ice detection, the pilots retain responsibility to monitor and detect ice accretions when an AIDS is installed. However, the natural tendency of flight crews to become accustomed to using the AIDS elevates the importance of the detector and increases the need to make flight crews aware of an AIDS failure. Therefore, an un-annunciated failure of the AIDS should be considered as at least a major failure condition unless substantiated as meriting a lower failure condition classification.

For the identification of conditions conducive to airframe icing in the frame of CS 25.1419(e)(3), the temperature cue used in combination with visible moisture has to be considered as a primary parameter, and the display of erroneous too high temperature to the flight crew, which potentially leads to non-activation of the IPS, should be considered as a catastrophic failure condition, unless substantiated as meriting a lower failure condition classification.

1.2  Visual cues

Visual cues can be either direct observation of ice accretions on the aeroplane’s protected surfaces or observation of ice accretions on reference surfaces. The first indications of any of the following are examples of what could potentially be used as visual cues:

             Accretions forming on the windshield wiper posts (bolt or blade).

             Accretions forming on propeller spinner.

             Accretions forming on radome.

             Accretions on the protected surfaces.

If accretions on protected surfaces cannot be observed, a reference system would be necessary if compliance with CS 25.1419(e)(2) is sought. The applicant should consider providing a reference surface that can be periodically de-iced to allow the flight crew to determine if the airframe is continuing to accumulate ice.

Without a means to de-ice the reference surface, as long as ice is present on the reference surface:

             The IPS should operate in presence of conditions conducive to icing (AFM procedure based on visible moisture and temperature); the IPS may be switched off after leaving conditions conducive to icing, even though ice may still be present on the reference surface; or

             The IPS should operate continuously, even if additional ice is not accumulating.

When ice accretion is no longer present on the reference surface, the next activation of the IPS can again be triggered by the presence of ice accreting on this reference surface.

As the freezing fraction drops below 1, although some reference surfaces may not build up ice, ice may begin to accumulate on protected surfaces of the aeroplane. The applicant should substantiate, for all the icing conditions defined in the relevant icing environment, that the reference surface accumulates ice at the same time as or prior to ice accumulating on the protected surfaces.

1.2.1  Field of view

Visual cues should be developed with the following considerations:

a.  Visual cues should be within the flight crew’s primary field of view, if possible. If cues are outside the primary field of view, they should be visible from the design eye point and easily incorporated into the flight crew’s vision scan with a minimum of head movement while seated and performing their normal duties.

b.  Visual cues should be visible during all modes of operation (day, night, and in cloud).

1.2.2  Verification

During the certification process, the applicant should verify the ability of the crew to observe the visual cues. Visibility of the visual cues should be evaluated from the most adverse flight crew seat locations in combination with the range of flight crew heights, within the approved range of eye reference point locations, if available. A visual cue is required for both the left and right seats. If a single visual cue is used, it should be visible from each seat. The adequacy of the visual cue should be evaluated in all expected flight conditions, and in particular the capability of detecting clear ice should be verified. The applicant may carry out night evaluations with artificial accretions to assess visibility in and out of cloud. Visual cues should be substantiated by tests and analysis, including tests in measured natural icing.

2.  Compliance With CS 25.1419(e)(3)

This subparagraph of CS 25.1419 provides an alternative to the PIDS and visual cues plus the AIDS as defined in CS 25.1419(e)(1) and (e)(2). This alternative requires operation of the IPS when the aeroplane is in conditions conducive to airframe icing during all phases of flight.

2.1  Temperature cue.

The temperature cue used in combination with visible moisture should consider static temperature variations due to local pressure variations on the airframe. If the engine IPS and the airframe IPS are both activated based on visible moisture and temperature, a common conservative temperature for operation of both systems should be used. For example, if the engine IPS is activated at + 5 ºC static air temperature or less, the airframe IPS should be activated at the same temperature, even if it is substantiated that the airframe will not accrete ice above + 2 ºC static air temperature. This would ease the flight crew workload and increase the probability of procedural compliance.

2.2  Either total or static temperatures are acceptable as cues. If static is used, a display of static air temperature should be provided to allow the flight crew to easily determine when to activate the systems. As an alternative, a placard showing corrections for the available temperature, to the nearest degree Celsius, can be used, so the flight crew can determine the static air temperature in the region of interest (that is, around 0 ºC).

2.3  Aeroplane Flight Manual (AFM).

The Limitations section of the AFM should identify the specific static or total air temperature and visible moisture conditions that must be considered as conditions conducive to airframe icing and should specify that the IPS must be operated when these conditions are encountered.

(e)  CS 25.1419(f)

This subparagraph of CS 25.1419 states that requirements of CS 25.1419(e)(1), CS 25.1419(e)(2) or CS 25.1419(e)(3) are applicable to all phases of flight unless it can be shown that the IPS need not be operated. To substantiate that the IPS need not be operated during certain phases of flight, the applicant should consider ice accretions that form during these phases, without the IPS operating, and establish that the aeroplane can safely operate in the relevant icing environment

(f)  CS 25.1419(g)

This subparagraph of CS 25.1419 requires that after the initial activation of the IPS:

             The IPS must operate continuously, or

             The aeroplane must be equipped with a system that automatically cycles the IPS, or

             An ice detection system must be provided to alert the flight crew each time the IPS must be cycled.

Some examples of systems that automatically cycle the IPS are:

             A system that senses ice accretion on a detector and correlates it to ice accretion on a protected surface. This system then cycles the IPS at a predetermined rate.

             A system that uses a timer to cycle the IPS. The applicant should substantiate that the aeroplane can safely operate with the ice accretions that form between the time one de-icing cycle is completed and the time the next cycle is initiated. If more than one cycling time is provided to the flight crew (for example choosing between a 1- or 3-minute intervals), it should be substantiated that the flight crew can determine which cycle time is appropriate.

             A system that directly senses the ice thickness on a protected surface and cycles the IPS.

A common attribute of the above systems is that the pilot is not required to manually cycle the IPS after initial activation.

Some types of ice detection systems that alert the flight crew each time the IPS must be cycled could operate in a manner similar to the automatic systems discussed above, except that the crew would need to manually cycle the system. Flight crew workload associated with such a system should be evaluated. Because of flight crew workload and human factors considerations, a timed system without an ice sensing capability should not be used to meet this requirement. The ice shedding effectiveness of the selected means for cycling the ice protection system should be evaluated during testing in natural icing conditions. All inter-cycle and runback ice should be considered when showing compliance with CS 25.21(g).

(g)  CS 25.1419(h)

CS 25.1419(h) requires that AFM procedures for operation of the IPS, including activation and deactivation, must be established. Procedures for IPS deactivation must be consistent with the CS 25.1419(e) requirements for activation of the IPS. The exact timing of deactivation should consider the type of ice protection system (e.g., de-icing, anti-icing, or running wet) and all delays in deactivation necessary to ensure that residual ice is minimized. Pneumatic boots should be operated for three complete cycles following the absence of the cues used for activation. However, if the aeroplane’s stall protection system reverts from an icing schedule to a non-icing schedule when the airframe IPS is deactivated, AFM procedures should state that the airframe IPS should not be deactivated until the flight crew are certain that the critical wing surfaces are free of ice.

[Amdt 25/16]

CS 25.1420 Supercooled large drop icing conditions

ED Decision 2016/010/R

(see AMC 25.1420)

(a)  If certification for flight in icing conditions is sought, in addition to the requirements of CS 25.1419, the aeroplane must be capable of operating in accordance with sub-paragraphs (a)(1), (a)(2), or (a)(3) of this paragraph.

(1)  Operating safely after encountering the icing conditions defined in Appendix O:

(i)  The aeroplane must have a means to detect that it is operating in Appendix O icing conditions; and

(ii)  Following detection of Appendix O icing conditions, the aeroplane must be capable of operating safely while exiting all icing conditions.

(2)  Operating safely in a portion of the icing conditions defined in Appendix O as selected by the applicant.

(i)  The aeroplane must have a means to detect that it is operating in conditions that exceed the selected portion of Appendix O icing conditions; and

(ii)  Following detection, the aeroplane must be capable of operating safely while exiting all icing conditions.

(3)  Operating safely in the icing conditions defined in Appendix O.

(b)  To establish that the aeroplane can operate safely as required in sub-paragraph (a) of this paragraph, an applicant must show through analysis that the ice protection for the various components of the aeroplane is adequate, taking into account the various aeroplane operational configurations. To verify the analysis, one, or more as found necessary, of the following methods must be used:

(1)  Laboratory dry air or simulated icing tests, or a combination of both, of the components or models of the components.

(2)  Laboratory dry air or simulated icing tests, or a combination of both, of models of the aeroplane.

(3)  Flight tests of the aeroplane or its components in simulated icing conditions, measured as necessary to support the analysis.

(4)  Flight tests of the aeroplane with simulated ice shapes.

(5)  Flight tests of the aeroplane in natural icing conditions, measured as necessary to support the analysis.

(c)  For an aeroplane certified in accordance with sub-paragraph (a)(2) or (a)(3) of this paragraph, the requirements of CS 25.1419(e), (f), (g), and (h) must be met for the icing conditions defined in Appendix O in which the aeroplane is certified to operate.

(d)  A comparative analysis may be used as an alternative to CS 25.1420(b) to establish that the aeroplane can operate safely as required in CS 25.1420(a), and as an alternative to CS 25.1420(c) regarding methods of icing detection and activation of the airframe ice protection system. In this case, tests may not be required (see AMC 25.1420(f)).

[Amdt 25/16]

[Amdt 25/18]

AMC 25.1420 Supercooled large drop icing conditions

ED Decision 2016/010/R

If certification for flight in icing conditions is sought, in addition to the requirements of CS 25.1419, the aeroplane must be capable of operating in accordance with subparagraphs (a)(1), (a)(2), or (a)(3) of CS 25.1420.  

Besides being able to operate safely in Appendix C icing conditions, the aeroplane must also be able to safely operate in or exit the icing conditions defined by CS-25, Appendix O. The applicant, however, has several certification options available for Appendix O icing conditions. The aeroplane can be certified for:

             The ability to detect Appendix O conditions and safely exit all icing conditions , or

             The ability to operate safely throughout a portion of Appendix O icing conditions and safely exit all icing conditions when that portion of Appendix O is exceeded, or

             The ability to operate safely throughout all Appendix O icing conditions.

In the context of this AMC:

             ‘Relevant icing environment’ means the Appendix O or a portion of the Appendix O as applicable.

             ‘All icing conditions’ means Appendix C and Appendix O icing environment.

             ‘Simulated Icing Test’ means testing conducted in simulated icing conditions, such as in an icing tunnel or behind an icing tanker.

             ‘Simulated Ice Shape’ means an ice shape fabricated from wood, epoxy, or other materials by any construction technique.

CS 25.1420 provides specific airframe requirements for certification for flight in the icing conditions defined in Appendix O. Additionally, for other parts of the aeroplane (i.e. engine, engine inlet, propeller, flight instrument external probes, windshield) there are more specific icing related CS-25 specifications and associated acceptable means of compliance.

Appendix O Spectra

Appendix O defines freezing drizzle and freezing rain environments by using four spectra of drop sizes with associated liquid water content (LWC) limits. An FAA detailed report on the development of Appendix O is available from the FAA William J. Hughes Technical Center (reference report DOT/FAA/AR-09/10, dated March 2009). Following are the four drop size spectra:

a) Freezing drizzle environment with a median volume diameter (MVD) less than 40 microns (μm). In addition to drizzle drops, which are defined as measuring 100 to 500 μm in diameter, this environment contains drops less than 100 μm, with a sufficient number of drops less than 40 μm so the MVD is less than 40 μm.

b)  Freezing drizzle environment with an MVD greater than 40 μm. In addition to freezing drizzle drops, this environment contains smaller drops, with diameters less than 100 μm.

c)  Freezing rain environment with an MVD less than 40 μm. In addition to freezing rain drops, which are defined as measuring more than 500 μm in diameter, this environment also contains smaller drops of less than 500 μm with a sufficient number of drops less than 40 μm so the MVD is less than 40 μm.

d)  Freezing rain environment with an MVD greater than 40 μm. In addition to freezing rain drops, this environment also contains smaller drops of less than 100 μm.

Caution information:

CS 25.1420 describes requirements that are in addition to the requirements in CS 25.1419 for certain aeroplanes and does not contain a requirement complementary to CS 25.1419(c). Instead, it relies on compliance with CS 25.1309(c) to ensure that adequate warning is provided to the flight crew of unsafe system operating conditions. Warning information required by CS 25.1309(c), to alert the flight crew of unsafe system operating conditions, is applicable to design features installed to meet the additional requirements in CS 25.1420 and must be provided in accordance with CS 25.1322.

(a)  CS 25.1420(a)(1) Detect Appendix O icing conditions and safely exit all icing conditions

When complying with CS 25.1420(a)(1), the applicant must provide a method for detecting that the aeroplane is operating in Appendix O icing conditions. Following detection, the aeroplane must be capable of operating safely while exiting all icing conditions until landing.

Substantiated methods of alerting flight crews when Appendix O icing conditions are encountered are required. It is acceptable to use an ice detection system that detects accretions behind the aeroplane’s protected areas. Considerations in paragraph (b) below, related to CS 25.1420(a)(2) acceptable means of alerting flight crews when Appendix O icing conditions are encountered, are also relevant for this paragraph.

(b)  CS 25.1420(a)(2) Operate safely throughout a portion of Appendix O icing conditions

If the applicant seeks certification for safe operation in portions of Appendix O icing conditions, such as freezing drizzle only, or during specific phases of flight, CS 25.1420(a)(2) applies. If this option is chosen, following detection of conditions that exceed the selected portion of Appendix O, the aeroplane must be capable of operating safely while exiting all icing conditions until landing.

Substantiated methods of alerting flight crews when those portions of Appendix O are exceeded are required.

Certification for flight in a portion of Appendix O icing conditions depends upon the applicant substantiating an acceptable way for the flight crew to distinguish the portion of Appendix O conditions for which the aeroplane is certified from the portion of Appendix O conditions for which the aeroplane is not approved. Certification for a portion of Appendix O allows latitude for certification with a range of techniques. Ice shapes will need to be developed to test for the portion of the envelope for which approval is sought, as well as for detecting and exiting icing conditions beyond the selected portion. The icing conditions the aeroplane may be certified to fly through may be defined in terms of any parameters that define Appendix O conditions and could include phase of flight limits, such as take-off or holding, in Appendix O or a portion of Appendix O. For example, an aeroplane may be certificated to take off in portions of Appendix O conditions, but not be certificated for holding in those same conditions. Substantiated means must be provided to inform flight crews when the selected icing conditions boundary is exceeded. The applicant must show compliance with CS 25.21(g) for exiting the restricted Appendix O icing conditions. Ice shapes to be tested are those representing the critical Appendix O icing conditions during recognition and subsequent exit from those icing conditions.

Ice shapes developed using the approved portion of the icing envelope should account for the range of drop distribution and water content and consider the proposed method for identifying icing conditions that must be exited. The definition of the certificated portion of Appendix O for a particular aeroplane should be based on measured characteristics of the selected icing environment and be consistent with methods used for developing Appendix O. Initial certification for flight in a portion of Appendix O conditions will likely include all of freezing drizzle or all of freezing rain. Such certification could be restricted to operation in Appendix O conditions by phase of flight.

Methods of defining the selected Appendix O icing conditions boundary should be considered early in the certification process, with concurrence from the Agency.

Determining whether the selected Appendix O icing conditions boundary has been exceeded can potentially be accomplished using:

             substantiated visual cues,

             an ice detection system, or

             an aerodynamic performance monitor.

The relevant AFM section(s) (possibly the limitation and the emergency procedure) should detail the method to warn the flight crew that the certified icing envelope has been exceeded.

1.  Substantiated visual cues

Substantiated visual cues can range from direct observation of ice accretions aft of the aeroplane’s protected surfaces to observation of ice accretions on reference surfaces. Methods used to substantiate visual cues should be agreed upon with the Agency. Responding to a visual cue should not require the flight crew to judge the ice to be a specific thickness or size.

Examples of potential visual cues are accretions forming on the side windshields, the sides of nacelles, the propeller spinners aft of a reference point, the radomes aft of a reference point, and/or aft of protected surfaces.

Visual cues should be developed with the following considerations:

(i)  Visual cues should be within the flight crew's primary field of view if possible. If outside the primary field of view, the visual cues should be visible from the design eye point and easily incorporated into the flight crew's visual scan with a minimum of head movement while seated and performing their normal duties.

(ii)  Visual cues should be visible during all modes of operation (day, night) without use of a handheld flashlight.

During the certification process, the applicant should verify the ability of the crew to observe visual cues or reference surfaces. Visibility of the visual cues should be evaluated from the most adverse flight crew seat locations in combination with the range of flight crew heights, within the approved range of eye reference point locations, if available. A visual cue is required for both the left and right seats. If a single visual cue is used, it should be visible from each seat. Consideration should be given to the difficulty of observing clear ice. The adequacy of the detection method should be evaluated in all expected flight conditions. The applicant may carry out night evaluations with simulated ice shapes to assess visibility in and out of cloud.

Visual cues should be substantiated by tests and analysis, including tests in measured natural icing, or icing tanker tests, or potentially through icing wind tunnel tests. The applicant should consider the drop distributions of Appendix O when developing the visual cue, and the applicant should substantiate that these cues would be present in all the restricted Appendix O icing conditions. If a reference surface is used, the applicant should substantiate that it accumulates ice at the same time as or prior to ice accumulation on the critical surfaces.

AMC 25.21(g) should be reviewed for guidance on the time flight crews need to visually detect Appendix O icing conditions.

2.  Ice detection systems

An ice detection system installed for compliance with CS 25.1420(a) is meant to determine when conditions have reached the boundary of the Appendix O icing conditions in which the aeroplane has been demonstrated to operate safely. The applicant should accomplish a drop impingement analysis and/or tests to ensure that the ice detector is properly located to function during the aeroplane operational conditions and in Appendix O icing conditions. The applicant may use analysis to determine that the ice detector is located properly for functioning throughout the drop range of Appendix O icing conditions when validated with methods described in document SAE ARP5903 “Drop Impingement and Ice Accretion Computer Codes”, dated October 2003. The applicant should ensure that the system minimizes nuisance warnings when operating in icing conditions.

The low probability of finding conditions conducive to Appendix O ice accumulation may make natural icing flight tests a difficult way to demonstrate that the system functions in conditions exceeding Appendix C. The applicant may use flight tests of the aeroplane under simulated icing conditions (icing tanker). The applicant may also use icing wind tunnel tests of a representative aerofoil section and an ice detector to demonstrate proper functioning of the system and to correlate signals provided by the detectors with the actual ice accretion on the surface.

3.  Aerodynamic performance monitor (APM)

A crew alerting system using pressure probes and signal processors could be developed for quantifying pressure fluctuations in the flow field from contamination over the wing surface. This technology does exist, but full development is necessary before incorporating it into the crew alerting system.

(c)  CS 25.1420(a)(3) Operate safely throughout all Appendix O icing conditions

CS 25.1420(a)(3) applies when the applicant seeks certification for all of the icing conditions described in Appendix O. An aeroplane certified to CS 25.1420(a)(3) must be capable of safely operating throughout the conditions described in Appendix O and does not need a means to distinguish Appendix O conditions from Appendix C conditions. The provisions in CS 25.1419 which require a method to detect icing conditions and activate the ice protection system are still applicable. If the aeroplane is certified for unrestricted flight in Appendix O conditions, the ice detection method must be substantiated to function throughout Appendix O. In effect, when CS 25.1420(a)(3) is chosen, the aeroplane is certificated for flight in icing without any specific aeroplane flight manual procedures or limitations to exit icing conditions.

If the AFM performance data reflects the most critical ice accretion (Appendix C and Appendix O) and no special normal or abnormal procedures are required in Appendix O conditions, then a means to indicate when the aeroplane has encountered Appendix O icing conditions is not required. However, a means to alert the flight crew that the airplane has encountered icing conditions is still required in accordance with CS 25.1419.

(d)  CS 25.1420 (b)

1.  Analysis

AMC 25.1419(a) applies and in addition, the following should be considered specifically for compliance with CS 25.1420(b):

1.1  Analysis of areas and components to be protected.

In assessing the areas and components to be protected, unless comparative analysis is used as the means of compliance, considerations should be given on the fact that areas that do not accrete ice in Appendix C conditions may accrete ice in the Appendix O conditions.

1.2  Failure analysis

Applying the system safety principles of CS 25.1309 is helpful in determining the need for system requirements to address potential hazards from an Appendix O icing environment. The following addresses application of the CS 25.1309 principles to Appendix O conditions and may be used for showing compliance with CS 25.1309. Alternatively, a comparative analysis, if applicable, may be used as defined in paragraph (e) of this AMC.

1.2.1  Hazard classification

Assessing a hazard classification for compliance with CS 25.1309 is typically a process combining quantitative and qualitative factors based on the assessment of the failure conditions and the associated severity of the effects. If the design is new and novel and has little similarity to previous designs, a hazard classification based on past experience may not be appropriate. If the design is derivative in nature, the assessment can consider the icing event history of similarly designed aeroplanes and, if applicable, the icing event history of all conventional design aeroplanes. The applicant should consider specific effects of supercooled large drop icing when assessing similarity to previous designs.

1.2.2  Qualitative Analysis

The following qualitative analysis may be used to determine the hazard classification for an unannunciated encounter with Appendix O icing conditions. The analysis can be applied to aeroplanes shown to be similar to previous designs with respect to Appendix O icing effects, and to which the icing event history of all conventional design aeroplanes is applicable.

1.2.2.1  Assumptions

The aeroplane is certificated to either:

a.  Detect Appendix O icing conditions and safely exit all icing conditions after detection of Appendix O icing conditions, or

b.  Safely operate in a selected portion of Appendix O icing conditions and safely exit all icing conditions after detection of Appendix O icing conditions beyond those for which it is certificated.

The ‘unannunciated encounter with Appendix O’ refers to Appendix O icing conditions in which the aeroplane has not been shown to operate safely.

The airframe and propulsion ice protection systems have been activated prior to the unannunciated encounter.

1.2.2.2  Service history

The applicant may use service history, design, and installation appraisals to support hazard classifications for CS 25.1309. Service history may be appropriate to support a hazard classification if a new or derivative aeroplane has similar design features to a previously certificated aeroplane. Service history data are limited to the fleet of aeroplane type(s) for which the applicant is the holder of the Type Certificate(s), the owner of the data, or, if accepted by the Agency, has an agreement in place with the owner of the data that permits its use by the applicant for this purpose (see also paragraph (f)3.2 of this AMC).

1.2.2.3  Historical perspective

While definitive statistics are not available, a historical perspective can provide some guidance. Many aeroplanes flying through icing have been exposed to supercooled large drop conditions without the pilot being aware of it. The interval of exposure to the supercooled large drop conditions may have varied from a brief amount of time (such as could occur during a vertical transition through a cloud) to a more sustained exposure (such as during a hold). Severity of the exposure conditions in terms of water content may have varied significantly. Therefore, the hazard from encountering supercooled large drop conditions may be highly variable and dependent on various factors.

1.2.2.4  Icing event history of aeroplanes of conventional design certified before the introduction of CS 25.1420.

Given the volume of aeroplane operations and the number of reported incidents that did not result in a catastrophe, a factor of around 1 in 100 is a reasonable assumption of probability for a catastrophic event if an aeroplane encounters the icing conditions represented by Appendix O Appendix O in which it has not been shown capable of safely operating, while the aeroplane’s ice protection systems are operating normally (in accordance with approved procedures for the icing conditions represented by Appendix C). An applicant may assume that the hazard classification for an unannunciated encounter with the icing conditions represented by Appendix O while these ice protection systems are operating normally is hazardous in accordance with AMC 25.1309, provided that the following are true:

             The aeroplane is similar to previous designs with respect to icing effects in the icing conditions represented by Appendix O, and

             The applicant can show that the icing event history of all aeroplanes of conventional design is relevant to the aeroplane being considered for certification.

1.2.2.5  Hazard assessment

If an aeroplane is not similar to a previous design, an assessment of the hazard classification may require more analysis or testing. One method of hazard assessment would be to consider effects of ice accumulations similar to those expected for aeroplanes being certified under CS 25.1420. Such ice shapes may be defined from a combination of analysis and icing tanker or icing wind tunnel testing. Aerodynamic effects of such shapes could be evaluated with wind tunnel testing or, potentially, computational fluid dynamics. Hazard classification typically takes place early in a certification program. Therefore, a conservative assessment may be required until sufficient supporting data is available to reduce the hazard classification.

1.2.3  Probability of encountering the icing conditions represented by Appendix O

Appendix C was designed to include 99 percent of icing conditions. Therefore, the probability of encountering icing outside of Appendix C drop conditions is on the order of 10-2. The applicant may assume that the average probability for encountering the icing conditions represented by Appendix O is 1 x 10-2 per flight hour. This probability should not be reduced based on phase of flight.

1.2.4  Numerical safety analysis.

For the purposes of a numerical safety analysis, the applicant may combine the probability of equipment failure with the probability, defined above, of encountering Appendix O icing conditions. If the applicant can support a hazard level of ‘Hazardous’ using the above probability (10-2) of encountering the specified supercooled large drop conditions, the probability of an unannunciated failure of the equipment that alerts the flight crew to exit icing conditions should be less than 1 x 105.

1.2.5  Assessment of visual cues.

Typical system safety analysis do not address the probability of crew actions, such as observing a visual cue before performing a specified action. As advised in AMC 25.1309, quantitative assessments of crew errors are not considered feasible. When visual cues are to be the method for detecting Appendix O conditions and determining when to exit them, the applicant should assess the appropriateness and reasonableness of the specific cues. Reasonable tasks are those for which the applicant can take full credit because the tasks can realistically be anticipated to be performed correctly when required. The applicant should assess the task of visually detecting Appendix O conditions to determine if it could be performed when required. The workload for visually detecting icing conditions should be considered in combination with the operational workload during applicable phases of flight. The applicant may assume that the flight crew is already aware that the aeroplane has encountered icing. The assessment of whether the task is appropriate and reasonable is limited to assessing the task of identifying Appendix O accumulations that require exiting from the icing conditions.

1.3  Similarity

On derivative or new aeroplane designs, the applicant may use similarity to previous type designs which have been certified for operation in SLD icing conditions, meanwhile the effects of differences will be substantiated. Natural ice flight testing may not be necessary for a design shown to be similar.

The guidance provided in AMC 25.1419(a)(8) applies.

The applicant must possess all the data required to substantiate compliance with applicable specifications, including data from past certifications upon which the similarity analysis is based.

2.  Tests

CS 25.1420 requires two or more means of compliance for approval of flight in icing, except when a comparative analysis is used to show compliance. It is common to use a combination of methods in order to adequately represent the conditions and determine resulting degradation effects with sufficient confidence to show compliance.

Some of the guidance contained in paragraph (b) of AMC 25.1419 may be relevant to this paragraph. In addition, with respect to natural icing flight testing in the Appendix O icing environment, CS 25.1420 does not specifically require measured natural icing flight tests. However, flight testing in measured natural Appendix O icing conditions may be necessary to:

(i)  verify the general physical characteristics and location of the simulated ice shapes used for dry air testing, and in particular, their effects on aeroplane handling characteristics.

(ii) determine if ice accretes on areas where ice accretion was not predicted.

(iii)  verify adequate performance of ice detectors or visual cues.

(iv)  conduct performance and handling quality tests as outlined in AMC 25.21(g).

(v)  evaluate effects of ice accretion not normally evaluated with simulated ice shapes (on propeller, antennas, spinners, etc.) and evaluate operation of each critical aeroplane system or component after exposure to Appendix O icing conditions.

Flight testing in natural Appendix O conditions would unlikely be necessary unless the aeroplane will be certified for continued operation within a portion or all of appendix O conditions. For aeroplanes to be certified to a portion or all of Appendix O, where natural Appendix O icing conditions flight testing is performed, measurement and recording of drop diameter spectra should be accomplished.

Flight testing in natural Appendix O icing conditions should be accomplished for aeroplane derivatives whose ancestor aeroplanes have a service record that includes a pattern of accidents or incidents due to in flight encounters with Appendix O conditions.

(e)  CS 25.1420(c)

CS 25.1420(c) requires that aeroplanes certified in accordance with subparagraph CS 25.1420(a)(2) or (a)(3) comply with the requirements of CS 25.1419(e), (f), (g), and (h) for the icing conditions defined in Appendix O in which the aeroplane is certified to operate.

Paragraphs (d), (e), (f), and (g) of AMC 25.1419 apply.

If applicable, a comparative analysis, as defined in AMC 25.1420(f), may be used to show compliance.

(f)  CS 25.1420(d) Comparative analysis

For showing compliance with the CS-25 certification specifications relative to SLD icing conditions as represented by Appendix O, the applicant may use a comparative analysis to show similarity of a new or derivative aeroplane model to existing model(s) with features and/or margins which are deemed to have contributed to a safe fleet history in all icing conditions.

When using comparative analysis as a means of compliance, flight testing in measured natural SLD icing conditions and/or flight testing with simulated ice shapes defined in accordance with Appendix O — part II is not required. Nevertheless, other types of tests may be required.

1.  Definitions

             Accident: The definition of the term ‘accident’ is provided in ICAO Annex 13, Chapter 1.

             Certification ice shapes/ice shape data: Ice shapes or ice shape data used to show compliance with certification specifications for flight in icing conditions. As used in this document, these are the ice shapes or data used to represent the critical ice shapes with the intent that they convey the ice that represents the most adverse effect on performance and flight characteristics. The data which is used to represent these shapes may be comprised of flight test data (artificial or natural ice), wind tunnel data, analytical data, or combinations of the above as allowed during previous certification projects.

             Comparative analysis:

             The use of analyses to show that an aeroplane is comparable to models that have previously been certified for operation in icing conditions via the environment represented by Appendix C and have a proven safe operating history in any supercooled liquid water icing conditions, but that may not have already been explicitly certified for operation in the icing environment represented by Appendix O.

             Key elements:

             The new or derivative model is certifiable for Appendix C icing conditions,

             Aeroplane models previously certified for Appendix C icing conditions are used to establish a reference fleet,

             The new or derivative model has similar design features and/or margins for key parameters relative to the reference fleet,

             The reference fleet has a safe fleet history in supercooled liquid water icing conditions.

             Events: Within this document the word ‘event’ means ‘accident and/or serious incident’ as defined in ICAO Annex 13, Chapter 1. For the purpose of identifying serious incidents with respect to the in-service history used for the comparative analysis, this should include reports where the flight crew encountered difficulties controlling the aeroplane, or temporarily lost its control, when flying in icing conditions.

             Key parameters: Parameters deemed to have contributed to the safe operation in icing conditions of the reference fleet. These parameters should be defined and provided by the applicant for each of the topics addressed using the comparative analysis. They should be agreed with the Agency.

             Reference fleet: The fleet of previously certified aeroplanes used to establish safe fleet history in order to enable the use of comparative analysis as a means of compliance.

             Serious incident: The definition of the term ‘serious incident’ is provided in ICAO Annex 13, Chapter 1.

             Similarity analysis:

             The direct comparison of a new or derivative aeroplane model to models already certified for operation in the icing environment of Appendix C and/or Appendix O. The similarity can be established for the aeroplane, the systems and/or the components.

             Key elements:

             Similar design features,

             Similar performance and functionality.

2.  Introduction

This paragraph introduces comparative analysis as a means of compliance with the CS-25 certification specifications addressing SLD icing conditions represented by Appendix O. The Agency acknowledges that there are a significant number of large aeroplane models which have an exemplary record of safe operation in all icing conditions, which inherently include SLD icing conditions. A comparative analysis provides an analytical certification path for new aeroplane models and derivatives by allowing the applicant to substantiate that a new or derivative model will have at least the same level of safety in all supercooled liquid water icing conditions that previous models have achieved.

For derivative models, the applicable certification specifications are determined through the application of the ‘Changed Product Rule (CPR)’. Rather than demonstrating compliance with the certification specifications in effect at the date of application, an applicant may demonstrate compliance with an earlier amendment of the certification specifications when meeting one of the conditions provided in Part-21, point 21.A.101(b). After application of the CPR, if the derivative model must comply with an amendment that includes the SLD-related certification specifications, compliance by comparative analysis may be used.

To use a comparative analysis as means of compliance for a new or derivative aeroplane model, four main elements should be established:

a.  A reference fleet with an adequately safe history in icing conditions;

b.  An analysis of aeroplane design features and/or margins that are deemed to contribute to the safe history of the reference fleet.

c.  A comparison showing that the new or derivative aeroplane model shares the comparable design features and/or margins, with the reference fleet.

d.  The compliance of the new or derivative aeroplane model with the applicable CS-25 certification specifications relative to flight in the icing conditions defined by Appendix C.

3.  Determining Adequately Safe Fleet History

In order to use a comparative analysis, a safe fleet history has to be established for the reference fleet of aeroplane model(s) to be used for comparison.

3.1 Fleet History Composition

The reference fleet should include the previous aeroplane model(s) sharing the design features and/or margins that will be used to substantiate the comparative analysis. The applicant should present to the Agency any known supercooled-liquid-water-icing-related accidents or serious incidents of the reference fleet. The applicant should present an analysis of any such events and explain how the identified root causes were addressed. Unless it can be justified, credit should not be taken for those flights of any aeroplane model that has experienced accidents or serious incidents due to flight in supercooled liquid water icing conditions. If design changes were made to correct deficiencies that contributed to or caused the accidents or serious incidents, including those which may have occurred in SLD, credit for flights may be taken only for the fleet of aeroplanes that have the changes incorporated (i.e. post-modification number of flights).

3.2  Use of Fleet History Data Not Owned by the Applicant

The use of fleet history data from the fleets of other certificate holders for Supplemental Type Certificate, new Type Certificate, or Major change to Type Certificate applications may be accepted by the Agency when formal agreements between the applicant and the certificate holder permitting the use of the relevant fleet history are in place. The Agency will determine the acceptability and the applicability of the data.

3.3  Applicability of Fleet History for the Certification Options of CS 25.1420(a)

When compiling data for aeroplane model(s) which will comprise the applicant’s reference fleet, operational limitations or restrictions imposed by either the AFM(s) or the operating manuals furnished by the TC holder for the model(s), should be considered. Relevant operational limitations existing for the reference fleet (e.g. AFM or operating manual prohibition against take-off into freezing drizzle or light freezing rain, direction to avoid such conditions in flight, directions to exit severe icing, etc.) will limit the certification options available for the use of a comparative analysis.

If the aeroplane model(s) proposed to be included in the applicant’s reference fleet has (have) limitations or restrictions applicable to SLD, the certification options for which comparative analysis could be used are limited to CS 25.1420(a)(1) or (a)(2). The applicant should demonstrate within the comparative analysis that the means of ice and/or icing condition detection for the reference fleet remain valid and are applicable to the new or derivative aeroplane.

3.4  Safe Fleet History Requirements

The reference fleet should have accumulated two million or more flights in total with no accidents or serious incidents in supercooled liquid water icing conditions aloft.

4.  Compliance with the Applicable CS-25 Certification Specifications Relative to Appendix C Icing Conditions

A comparative analysis is an acceptable means of compliance only with the CS-25 certification specifications relative to Appendix O icing conditions. The use of a comparative analysis is not an option for showing compliance with CS-25 certification specifications relative to Appendix C icing conditions.

5.  Conducting Comparative Analysis

If a safe fleet history in icing conditions can be substantiated, and compliance with the CS-25 certification specifications for safe flight in Appendix C icing conditions can be shown, then the reference fleet can be used for comparative analysis. The substantiation of the reference fleet’s design features and/or margins which have contributed to the safe fleet history can be used for a new or derivative model having comparable design features and/or margins, to show compliance with the CS-25 certification specifications relative to flight in SLD icing conditions. When conducting a comparative analysis, the effects of key parameters for individual components or systems should be considered at the aeroplane level. A different design feature or margin may be shown to be acceptable when considered at the aeroplane level, taking into account the other aircraft design features and margins that are deemed to contribute to safe flight in icing conditions. The following aspects should be addressed:

a.  Ice protection systems,

b.  Unprotected components,

c.  Ice or icing conditions detection,

d.  Ice accretion and ice shedding sources,

e.  Performance and handling characteristics,

f.  Aeroplane Flight Manual information,

g.  Additional considerations — Augmenting comparative analysis

5.1  Applicable CS-25 certification specifications

The applicable certification specifications relative to SLD icing are listed in Table 1 below. This guidance is applicable to these certification specifications.

Table 1: List of applicable CS 25 certification specifications

Reference

Title

CS 25.21(g)

Performance and Handling Characteristics in Icing Conditions

CS 25.629

Aeroelastic stability requirements

CS 25.773(b)(1)(ii)

Pilot compartment view — icing conditions

CS 25.773(b)(4)

Pilot compartment view — non-openable windows

CS 25.929(a)

Propeller de-icing

CS 25 1093(b)

Powerplant icing — turbine engines

CS 25.1324

Flight instrument external probes

CS 25.1329

Flight Guidance System

CS 25.1403

Wing icing detection lights

CS 25.1420

Supercooled large drop icing conditions

CS 25J1093

Air intake system icing protection

5.2  Ice Protection Systems

The applicant should demonstrate similar levels of protection against the effects of ice accretion at the aeroplane level in the icing conditions of Appendix C. In doing so, the applicant should consider the ice protection system performance, modes of operation and the other factors identified by the applicant that contribute to the overall safety of the aeroplane for flight in the icing conditions of Appendix C. The assessment could include, but is not necessarily limited to, an analysis of the protection limits relative to supercooled liquid water impingement limits, runback and residual ice, as applicable.

5.3  Failure Analysis

The reference fleet will have been certified considering only the supercooled liquid water icing conditions of Appendix C and will have demonstrated an adequate level of safety when flying in both Appendix C and SLD icing conditions. Therefore, if a comparative analysis is used as a means of compliance with the CS-25 certification specifications relative to Appendix O icing conditions, the ice protection system for a new or derivative aeroplane, and the related equipment or components comprising the system, should demonstrate a reliability level consistent with a Functional Hazard Assessment (FHA) as per CS 25.1309(b). The classification and assessment of failure conditions need only consider the effects of Appendix C icing conditions.

5.4  Ice or Icing Conditions Detection

If the new or derivative model being certified has similar ice and/or icing conditions detection means as the reference fleet, including installation and operational considerations (e.g. flight crew procedures), then a comparative analysis may be used to show compliance with Appendix O-related certification specifications.

If the applicant chooses to introduce a new ice and/or icing conditions detection technology and show compliance at the aeroplane level based on a reference fleet with unrestricted operations, and the applicant is seeking certification by comparative analysis for unrestricted operations in SLD icing conditions for the new or derivative model per CS 25.1420(a)(3), the new ice and/or icing conditions detection technology should be installed and operate in a manner that results in equivalent ice and/or icing conditions detection performance. This may include additional qualification to the icing conditions represented by Appendix C.

If the certification option chosen requires a differentiation between icing conditions (CS 25.1420(a)(1) or (a)(2)), then either the reference fleet should have demonstrated the ability to detect that the aeroplane is operating in conditions that exceed the conditions selected for certification (i.e. for CS 25.1420(a)(1), any Appendix O icing conditions; and for CS 25.1420(a)(2), the icing conditions that are beyond the selected portion of Appendix O), or the ice and/or icing conditions detection means should be substantiated for detection of the applicable Appendix O icing conditions at the aeroplane level.

If the reference fleet has achieved the required number of flights to enable the use of a comparative analysis to show compliance with the CS-25 certification specifications relative to Appendix O, then Appendix C may be used to show compliance with the certification specifications related to ice accretions before the ice protection system has been activated and is performing its intended function (e.g. CS 25.1419(e), CS 25.143(j) and CS 25.207(h)).

5.5  Unprotected Components

For systems that are required to operate in Appendix O icing conditions but do not require ice protection provisions, for example the Autopilot (CS 25.1329), wing illumination lights (CS 25.1403), unprotected environmental control system (ECS) intakes (CS 25.1420), etc., a comparative analysis may be used if design features are shown to be similar to those of the reference fleet.

5.6  Ice Accretion and Ice Shedding Sources

If a comparative analysis is used as the means of compliance with the CS-25 certification specifications relative to Appendix O icing conditions, certification ice shapes/ice data determined for Appendix C icing conditions are acceptable without additional Appendix O considerations. The locations where ice accretions may occur on the new or derivative model should be reviewed and compared to those of the reference fleet. The following aspects should be considered:

i.  An analysis showing that, in Appendix C icing conditions, the propulsion system and APU installation are such that the geometry and water catch of potential sources of ice shedding are similar to those used to establish the reference fleet history database.

ii.  A comparison of the location of, or the methodology for locating, flight instrument external probes to assure that the effect of airframe ice accretion forward of the probes will be comparable for the new or derivative model with that of the reference fleet relative to safe flight in the icing conditions of Appendix C.

iii.  For aeroelastic analyses, performance of an analysis showing ice accretion consistency (location and volume), defined using the icing conditions of Appendix C.

5.7  Aeroplane Performance and Handling Characteristics

The comparative analysis should substantiate that the effects of ice accretion and the agreed key parameters of the new or derivative model are comparable to those of the reference fleet. The applicant should substantiate by analysis, test, or a combination of both, that the new or derivative aeroplane will have similar margins to those of the reference fleet for flight in the icing conditions of Appendix C.

The following paragraphs provide guidance on how to achieve the above:

             Aeroplane performance,

             Aeroplane controllability and manoeuvrability,

             Aeroplane trim,

             Aeroplane stability,

             Aeroplane stalls.

5.7.1  Performance

The effects on aeroplane performance of the certification ice shapes/ice shape data determined for flight in the icing conditions of Appendix C for the new or derivative model should be comparable to those of the reference fleet. A comparison of ice accretion effects on lift and drag may be used in this analysis.

If comparable effects to those of the reference fleet cannot be shown, then the applicant should show how margins similar to those of the reference fleet are restored for the new or derivative model by other means that compensate for the effect (e.g. airspeed increase, sizing criteria, or other aeroplane limitations).

5.7.2  Controllability and Manoeuvrability

The effectiveness of the control surfaces and the control forces for the new or derivative model, with the certification ice shapes/ice shape data for flight in the icing conditions of Appendix C, should be comparable to those of the reference fleet. If critical Appendix C ice shapes affect the control surface effectiveness or control forces in a manner which may be different to that of the reference fleet, then the applicant should show how the control effectiveness and forces are retained.

The manoeuvrability associated with the certification ice shapes/ice shape data determined for the icing conditions of Appendix C should be comparable to those of the aeroplanes which comprise the reference fleet. If critical Appendix C ice shapes affect manoeuvrability in a manner which may be different to that of the reference fleet, then the applicant should show how the margins are retained (speed increase, etc.).

5.7.3  Trim

In addition to showing that trim capability for the new or derivative model, with the certification ice shapes/ice shape data for flight in the icing conditions of Appendix C, is comparable to that of the reference fleet, the margins between the required trim in the most critical conditions and the trim capability in Appendix C icing conditions should be comparable to those of the reference fleet.

5.7.4  Stability

The aeroplane stability associated with the certification ice shapes/ice shape data determined for the icing conditions of Appendix C should be comparable to those of the reference fleet. If this cannot be shown, then the applicant should show how similar stability margins are retained (speed increase, sizing criteria, other aircraft limitations, etc).

5.7.5  Stalls

a.  Stall warning and protection features

Stall warning, stall protection, and/or airspeed awareness methods, devices, and/or systems as applicable should be shown by comparative analysis to be similar in function or improved relative to those of the reference fleet.

b.  Stall warning margins

 Stall warning margins established with the certification ice shapes/ice shape data associated with flight in the icing conditions of Appendix C should be comparable to those of the reference fleet.

c.  Stall characteristics

The stall characteristics demonstrated by the new or derivative model with the certification ice shapes/ice shape data for flight in the icing conditions of Appendix C should be comparable to those of the reference fleet.

d.  Aeroplane with Flight Envelope Protection

 It should be shown that the new or derivative aeroplane and the reference fleet aeroplane(s) high angle-of-attack protection systems have a comparable ability to accommodate any reduction in stalling angle of attack with the certification ice shapes/ice shape data for flight in the icing conditions of Appendix C relative to the clean aeroplane.

 The high angle-of-attack characteristics demonstrated with the certification ice shapes/ice shape data for flight in the icing conditions of Appendix C should be comparable to those of the reference fleet.

5.8  Aeroplane Fight Manual Information

If the certification option chosen for the new or derivative model being certified (CS 25.1420(a)(1), (a)(2), or (a)(3)) is consistent with the operation of the reference fleet, then the information to be provided in the AFM may be based on that provided in the reference fleet AFM(s) or other operating manual(s) furnished by the TC holder.

5.9  Additional Considerations — Augmenting Comparative Analysis

In addition to the use of design features and/or margins, to substantiate a new or derivative design by comparative analysis, the applicant may augment the comparative analysis with other methodologies (e.g. test, analysis or a combination thereof). The new methodologies should be agreed with the Agency.

[Amdt 25/16]

[Amdt 25/18]

CS 25.1421 Megaphones

ED Decision 2003/2/RM

If a megaphone is installed, a restraining means must be provided that is capable of restraining the megaphone when it is subjected to the ultimate inertia forces specified in CS 25.561(b)(3).

CS 25.1423 Public address system

ED Decision 2006/005/R

A public address system required by operational rules must –

(a) Be powerable when the aircraft is in flight or stopped on the ground, after the shutdown or failure of all engines and auxiliary power units, or the disconnection or failure of all power sources dependent on their continued operation, for –

(1) A time duration of at least 10 minutes, including an aggregate time duration of at least 5 minutes of announcements made by flight and cabin crew members, considering all other loads which may remain powered by the same source when all other power sources are inoperative; and

(2) An additional time duration in its standby state appropriate or required for any other loads that are powered by the same source and that are essential to safety of flight or required during emergency conditions.

(b) The system must be capable of operation within 3 seconds from the time a microphone is removed from its stowage by a cabin crew member at those stations in the passenger compartment from which its use is accessible.

(c) Be intelligible at all passenger seats, lavatories, and cabin crew member seats and work stations.

(d) Be designed so that no unused, un-stowed microphone will render the system inoperative.

(e) Be capable of functioning independently of any required crewmember interphone system.

(f) Be accessible for immediate use from each of two flight-crew member stations in the pilot compartment.

(g) For each required floor-level passenger emergency exit which has an adjacent cabin crew member seat, have a microphone which is readily accessible to the seated cabin crew member, except that one microphone may serve more than one exit, provided the proximity of the exits allows unassisted verbal communications between seated cabin crew members.

[Amdt 25/2]