CS AWO.B.CATIII.101 Applicability
ED Decision 2022/007/R
This section is applicable to aeroplanes for which certification is sought to allow the performance of approaches with DHs below 30 m (100 ft) or with no DH — Category III operations, using a precision approach system as defined in ICAO Annex 10.
The criteria are divided, where necessary, into those applicable to the following types of operation:
(1) DHs below 30 m (100 ft) but not less than 15 m (50 ft);
(2) DHs below 15 m (50 ft); and
(3) No DH.
(See AMC AWO.B.CATIII.101(a))
[Issue: CS-AWO/2]
AMC AWO.B.CATIII.101(a) Applicability and terminology
ED Decision 2022/007/R
A precision approach system, as defined in ICAO Annex 10, is considered an xLS (ILS, MLS or GLS) which has outputs that indicate the magnitude and sense of deviation from a preset azimuth and elevation angle giving operational characteristics equivalent to those of a conventional ILS.
An aeroplane with a basic airworthiness approval for IFR operations is eligible to perform xLS precision approaches down to a DH of 60 m (200 ft), assuming that the necessary xLS receiver(s) and instruments and their installation have been approved. The supplementary airworthiness criteria for aeroplanes to perform precision approaches down to a DH below 60 m (200 ft) and down to 30 m (100 ft) are contained in Subpart B Section 3.
The purpose of this Section is to specify the supplementary airworthiness criteria for aeroplanes to perform precision approaches with DHs below 30 m (100 ft) or with no DH.
This material may not be appropriate to precision approach aids other than xLS. It should be noted that when other guidance information is used to supplement the xLS (e.g. inertial navigation systems), some reduction may be acceptable in the standard of xLS ground facility indicated below.
Terminology
(a) The term ‘landing system’ used here refers only to the airborne system. It includes the equipment listed in CS AWO.B.CATIII.113, and also all related sensors, instruments and power supplies.
(b) ‘Automatic landing system’: the airborne equipment which provides automatic control of the aeroplane during approach and landing.
(c) ‘Fail-passive automatic landing system’: an automatic landing system is fail-passive if, in the event of a failure, there is no significant out-of-trim condition or deviation of the flight path or attitude but the landing is not completed automatically.
(d) For a fail-passive automatic landing system, the pilot assumes control of the aircraft following a failure.
The following are typical arrangements:
(1) A monitored automatic pilot in which automatic monitors will provide the necessary failure detection and protection.
(2) Two automatic pilots with automatic comparison to provide the necessary failure detection and protection.
(e) ‘Super fail-passive automatic landing system’: an automatic landing system which meets the requirements of point (c) but has additional features such as automatic align, roll-out and go‑around modes which, along with other aircraft characteristics defined under CS AWO.B.CATIII.113(b)(2), permit operations in lower RVRs than less sophisticated fail-passive landing systems.
(f) ‘Fail-operational automatic landing system’: an automatic landing system is fail-operational if, in the event of a failure, the approach, flare and landing can be completed by the remaining part of the automatic system.
In the event of a failure, the automatic landing system will operate as a fail-passive system.
The following are typical arrangements:
(1) Two monitored automatic pilots, one remaining operative following a failure.
(2) Three automatic pilots, two remaining operative (to permit comparison and provide necessary failure detection and protection) following a failure.
(g) ‘Fail-operational hybrid landing system’: a system which consists of a primary fail-passive automatic landing system and a secondary independent guidance system enabling the pilot to complete a landing manually following a failure of the primary system.
A typical secondary independent guidance system consists of a monitored HUD providing guidance which normally takes the form of command information, but it may alternatively be situation (or deviation) information.
(h) The alert height is a specified radio height, based on the characteristics of the aeroplane and its fail-operational landing system. In operational use, if a failure occurred above the alert height in one of the required redundant operational systems in the aeroplane (including, where appropriate, ground-roll guidance and the reversionary mode in a hybrid system), the approach would be discontinued and a go-around executed unless reversion to a higher DH is possible. If a failure in one of the required redundant operational systems occurred below the alert height, it would be ignored and the approach continued.
(i) DH is the wheel height above the runway elevation by which a go-around must be initiated unless adequate visual reference has been established and the aircraft position and approach path have been assessed as satisfactory to continue the approach and landing safely.
Where ‘DH’ is used in this document, it means the minimum DH determined in the airworthiness certification.
(j) A go-around is the transition from an approach to a stabilised climb.
(k) Head-up display landing system (HUDLS)
The term ‘HUDLS' refers to the total airborne system which provides head-up guidance to the pilot during the approach, landing or go-around. It includes all the sensors, computers, power supplies, indications and controls. Typically, a HUDLS is used for primary approach guidance for DHs down to 15 m (50 ft).
The terms ‘localiser’ and ‘glide path’ have been retained for use with either ILS, MLS or GLS.
Cross reference is made in this Section to AMC AWO.A.ALS.110 which provides guidance on controls, indicators and alerts associated with installations incorporating more than one type of approach system (e.g. ILS and MLS and/or GLS).
Characteristics of the types of operation
Additional and more detailed information regarding the characteristics of the types of operation is provided below.
(a) DH below 30 m (100 ft) but not less than 15 m (50 ft)
The RVR required by a pilot to make the decision to land from a DH below 30 m (100 ft) is less than the RVR required for a DH at 30 m (100 ft). Furthermore, the time from the DH to the start of the flare manoeuvre will be less.
Consequently, in order to achieve the desired success rate and to preserve the safety level, it has been considered necessary that the aeroplane be fitted with an automatic landing system or a head-up landing guidance system. Use of such systems also ensures that the aeroplane is within the obstacle-free zone specified in ICAO Annex 14 during approach and any go-around so that there is no need to take obstacle clearance into account in determining the DH. The RVR limit is set by the responsible national authority in accordance with applicable operating regulations and provides an assessment of the visibility conditions at and below the DH so that, if either the landing system or the xLS signal-in-space fails when the aeroplane is below the DH, the pilot can carry out a manual landing with an acceptable safety level.
The ground guidance system is either:
(1) a Facility Performance Category III or a Facility Performance Category II ILS that complies with the Facility Performance Category III standards of ICAO Annex 10, Chapter 3-1, in respect of all significant performance parameters, at least down to ILS point D, 900 m (3 000 ft) from the runway threshold;
or
(2) a Category III MLS that complies with the requirements of ICAO Annex 10, Chapter 3.11;
Or
(3) a GAST D GLS that complies with the requirements of ICAO Annex 10
(b) DH below 15 m (50 ft)
Aeroplanes which have a fail-operational landing system, can be certified for operation with a DH below 15 m (50 ft).
In this type of operation, the RVR needs not only to be sufficient for the pilot to make the decision at the DH, but also to be sufficient to enable the pilot to control the aeroplane during the ground roll. The main purpose of the DH is so that the pilot can assess the adequacy of the visibility conditions before touchdown and prepare to take over visual manual control. It is desirable that the DH be late in the flare after the major pitch changes have taken place, and that an automatic go-around system be fitted. There exists an unknown probability that, although the RVR is reported to be adequate, denser patches of fog may lie on the runway, and it is thought prudent to add a margin to the bare minimum required to control the ground roll. The RVR limit is set by the responsible national authority in accordance with the applicable operating regulations.
The ground guidance system (xLS) is as described in point (a), and, additionally, comply with a continuity of service objective (failure survival capability) of 1–(2 x 10-6). It is assumed that the pilot is promptly notified by air traffic control (ATC) of a failure or degradation of the required ground equipment (e.g. loss of the stand-by xLS transmitter).
(c) No DH
An aeroplane with a fail-operational landing system with automatic ground-roll control (or ground-roll guidance) may be certified for operation without a DH (operations when the pilot is not required to make a decision described in the definition of DH). Any required RVR limit is set by the responsible national authority in accordance with the applicable operating regulations.
In these visibility conditions, the pilot is likely to brake hard during the ground roll and, therefore, an anti-skid braking system is considered essential. Distance and ground speed indications and automatic braking would obviously be useful, but are not considered essential and are not required.
The ground guidance system (Facility Performance Category III ILS, Category III MLS or GAST D GLS) complies with the Standards of ICAO Annex 10 and, additionally, complies with an integrity objective of 1–(0.5 x 10-9) ) and an ILS/MLS continuity of service objective of 1–(2 × 10–6) or a GLS continuity of service objective as stated in ICAO Annex 10, Appendix B, paragraph 3.6.7.1.3.2.
[Issue: CS-AWO/2]
CS AWO.B.CATIII.102 Safety level
ED Decision 2022/007/R
The safety level for precision approaches with DHs below 30 m (100 ft) or no DH may not be less than the average safety level achieved in precision approaches with DHs of 60 m (200 ft) and above.
[Issue: CS-AWO/2]
AMC AWO.B.CATIII.102 Safety level
ED Decision 2022/007/R
The safety level, achieved by complying with the performance and failure requirements of this Section, should be equivalent to or better than the safety level for operations with DHs of 60 m (200 ft) or above. Hence, in showing compliance with the performance and failure requirements, the probabilities of performance or failure effects should not be factored by the proportion of approaches, which are made with the DHs below 30 m (100 ft).
[Issue: CS-AWO/2]
CS AWO.B.CATIII.103 Go-around rate
ED Decision 2022/007/R
The go-around rate below 150 m (500 ft) attributable to the landing system performance or reliability shall not be greater than 5 %. Additionally, for DHs below 15 m (50 ft) and no DH, the probability of go-around below the alert height attributable to the landing system performance and reliability shall be such that compliance with CS AWO.B.CATIII.102 is achieved. (See CS AWO.B.CATIII.123(a))
[Issue: CS-AWO/2]
CS AWO.B.CATIII.104 Minimum flight crew
ED Decision 2022/007/R
The workload associated with the use of the minimum DH shall be considered in showing compliance with CS 25.1523, AMC 25.1523, and CS-25 Appendix D.
[Issue: CS-AWO/2]
CS AWO.B.CATIII.105 Control of flight path and ground roll
ED Decision 2022/007/R
(a) Landing systems, other than HUDLS, shall control the aeroplane within the prescribed limits along the flight path to touchdown (see CS AWO.B.CATIII.115(a) and (b)) and along the runway (see CS AWO.B.CATIII.117) when appropriate, and specifically:
(1) For fail-passive automatic landings, the primary mode of controlling the aeroplane shall be automatic until the main wheels touch the ground (except as in CS AWO.B.CATIII.113(b)(1)), and for operation with no DH, the control shall be automatic until the nose wheels touch down.
(2) For DHs below 15 m (50 ft), a fail-operational landing system (automatic or hybrid) shall be provided which, when appropriate, includes provision for the control of the aeroplane along the runway during the ground roll down to a safe speed for taxiing.
(3) If the landing roll-out is to be accomplished automatically using rudder control, the rudder axis shall be engaged during the approach phase.
(b) For HUDLs, the following applies:
(1) The system shall provide sufficient guidance information to enable a pilot that is competent to conduct the intended operation to intercept the xLS approach path, if that capability is provided, to track it, to land the aeroplane within the prescribed limits or to perform a go-around without reference to other cockpit displays. It shall not require exceptional piloting skill to achieve the required performance. (See CS AWO.B.CATIII.115(a) and (b))
(2) If the autopilot is used to control the flight path of the aeroplane to intercept and establish the xLS approach path, the point during the approach at which the transition from automatic to manual flight takes place shall be identified and taken into account in the performance demonstration (see CS AWO.B.CATIII.115).
[Issue: CS-AWO/2]
CS AWO.B.CATIII.106 Control of speed
ED Decision 2022/007/R
Automatic speed control shall be provided unless:
(a) the DH is 15 m (50 ft) or greater; and
(b) it is demonstrated in flight that speed can be controlled manually by the flight crew within the acceptable limits and without excessive workload. (See CS AWO.A.ALS.105 and AMC AWO.B.CATII.113)
[Issue: CS-AWO/2]
CS AWO.B.CATIII.107 Manual control
ED Decision 2022/007/R
The transition from an automatic mode to manual mode or the use of a manual mode shall not require exceptional piloting skill, alertness or strength.
[Issue: CS-AWO/2]
CS AWO.B.CATIII.108 Oscillations and deviations
ED Decision 2022/007/R
The landing system shall not cause sustained nuisance oscillations or undue attitude changes or control activity as a result of configuration or power changes or any other disturbance to be expected in normal operation.
[Issue: CS-AWO/2]
CS AWO.B.CATIII.109 Alert height
ED Decision 2022/007/R
(See AMC AWO.B.CATIII.109)
For a fail-operational system with a DH below 15 m (50 ft) or with no DH, an alert height shall be established in accordance with CS AWO.B.CATIII.123(a) and shall be at least 30 m (100 ft).
[Issue: CS-AWO/2]
AMC AWO.B.CATIII.109 Alert height
ED Decision 2022/007/R
(See CS AWO.B.CATIII.109)
It may be operationally useful for the alert height to be somewhat higher than 30 m (100 ft) since this would permit reversion to a higher DH in the event of system failure. A maximum value should be established during certification and it should not normally be above 90 m (300 ft).
[Issue: CS-AWO/2]
CS AWO.B.CATIII.110 Decision height
ED Decision 2022/007/R
When the DH is during the landing flare, it shall be below the height at which the major attitude changes associated with this manoeuvre take place.
[Issue: CS-AWO/2]
CS AWO.B.CATIII.111 Decision height recognition
ED Decision 2022/007/R
The recognition of the DH shall be made by means of height measured by a radio altimeter (or other device capable of providing for equivalent performance and integrity level). Arrival at the DH shall be positively annunciated to both pilots.
[Issue: CS-AWO/2]
ED Decision 2022/007/R
(See AMC AWO.B.CATIII.112)
(a) The aircraft shall be capable of safely executing a go-around from any point on the approach to touchdown in all configurations to be certified. The manoeuvre shall not require exceptional piloting skill, alertness or strength and shall ensure that the aeroplane remains within the obstacle limitation surface for a Category II or III precision approach runway as specified in ICAO Annex 14.
(b) For DHs below 15 m (50 ft), automatic go-around shall be provided.
(c) When automatic go-around is provided, it shall be available down to touchdown.
(d) When automatic go-around is engaged, the subsequent ground contact shall not cause its disengagement.
[Issue: CS-AWO/2]
AMC AWO.B.CATIII.112 Go-around
ED Decision 2022/007/R
1 Safety considerations
1.1 Effects of contact with the runway
For aircraft for which a go-around from a very low altitude may result in inadvertent runway contact, the safety of the procedure should be established giving consideration to at least the following:
a. The guidance information and control provided by the go-around mode should be retained and be shown to have safe and acceptable characteristics throughout the manoeuvre.
b. Other systems (e.g. automatic throttle, brakes, spoilers, reverse thrust and alerting systems) should not operate in a way that would adversely affect the safety of the go-around manoeuvre.
1.2 Inadvertent go-around selection
The inadvertent selection of the go-around mode after touchdown should have no adverse effect on the ability of the aircraft to safely roll out and stop.
2 Performance
Height loss from a range of altitudes during the approach and flare should be determined when under automatic control and when using the landing guidance system as appropriate.
a. Height loss may be determined by flight testing (with typically 10 flight-demonstrated go‑arounds) supported by simulation.
b. The simulation should evaluate the effects of variation in parameters such as weight, centre of gravity (CG), configuration and wind, and show correlation with the flight test results.
c. Normal procedures for a go-around with all engines operating should be followed.
[Issue: CS-AWO/2]