CS ACNS.E.TAWS.010 Required Functions and Interfaces

ED Decision 2013/031/R

(See AMC1 ACNS.E.TAWS.010, AMC2 ACNS.E.TAWS.010)

TAWS Class A or Class B provides suitable alerting and warning capabilities and other system interfaces to support the following functions:

AMC1 ACNS.E.TAWS.010 Required functions

ED Decision 2022/008/R

Note: An example of an acceptable TAWS installation is provided in Appendix B – Example of an acceptable TAWS installation. Guidance on testing a TAWS is provided in Appendix A – TAWS installations testing guidance material.

(a) For the voice call-out, a predetermined altitude of 150 m (500 ft) has been found acceptable. However, another altitude may be allowed when a call-out at 150 m (500 ft) would interfere with other operations.

(b) For Class B equipment the predetermined altitude voice callout is based upon barometric height above runway elevation.

Note: The nearest runway elevation may be used for this purpose.

(c) TAWS equipment may compute Barometric Altitude Rate using an Instantaneous Vertical Speed Indicator (IVSI) or an inertial smoothed vertical speed indicator. An alternative means, with demonstrated equal or better accuracy, may be used in lieu of barometric altitude rate (accuracy specified in ETSO-C10b, Altimeter, Pressure Actuated, Sensitive Type, or later revisions) and/or altimeter altitude (accuracy specified in ETSO-2C87 (Low range radio altimeters) - or later revisions) to meet the warning requirements described in RTCA Document No. DO-161A. In addition, ETSO-C106 for Air Data Computers may be used as an alternative means of compliance with this provision.

(d) An interface with the accident data recording system to record alerts from the TAWS and to record, where practicable, when FLTA or PDA is inhibited.

Note 1: It is not necessary to be able to distinguish between the Basic GPWS and the new FLTA and/or PDA alerts from the recording. The voice recorder will be used for this purpose.

Note 2: Where the data recorded by the Flight Data Recorder is modified, the document which presents the information necessary to retrieve and convert the stored data into engineering units, will need to be amended by the operator.

[Issue: CS-ACNS/4]

AMC2 ACNS.E.TAWS.010 Required functions

ED Decision 2013/031/R

In case of descent the TAWS should provide an automatic call out when descending through a predefined altitude (typically 150 m (500 ft) above terrain or above the elevation of nearest runway).

For a Class B TAWS in order to compensate for the lack of ‘excessive closure rate to terrain’ function the predefined altitude should be 500ft.

CS ACNS.E.TAWS.015 FLTA function requirements

ED Decision 2013/031/R

(See AMC1 ACNS.E.TAWS.015)

Provide an FLTA function that:

(a) Provides an Forward Looking Terrain Avoidance (FLTA) function that looks ahead of the airplane along and below the airplane’s lateral and vertical flight path and provides suitable alerts if a potential CFIT threat exists.

(b) Provides a Required Terrain Clearance (RTC) alerts when the aeroplane is currently above the terrain in the aeroplane’s projected flight path but the projected amount of terrain clearance is considered unsafe for the particular phase of flight.

TABLE 1

(c) gives Imminent Terrain Impact alerts when the aeroplane is currently below the elevation of a terrain cell along the aeroplane’s lateral projected flight path and, based upon the vertical projected flight path, the equipment predicts that the terrain clearance will be less than the value given in the RTC column of Table 1.

(d) gives alerts for the Imminent Terrain Impact and Required Terrain Clearance functions when the aeroplane is in turning flight.

AMC1 ACNS.E.TAWS.015 FLTA function requirements

ED Decision 2013/031/R

(a) The TAWS lateral search area should be less than the protected area defined by ICAO PANS OPS 8168, volume 2 to prevent nuisance alerts.

Note: The required obstacle (terrain) clearance (ROC) have been used to define the minimum requirements for obstacle/terrain clearance (RTC) appropriate to the FLTA function

(b) As an alternate to the stepped down reduction from the terminal to approach phase in CS ACNS.E.TAWS.015 Table 1 , a linear reduction of the RTC as the aeroplane comes closer to the nearest runway is allowed, providing the requirements of CS ACNS.E.TAWS.015 Table 1 are met.

(c) During the visual segment of a normal instrument approach (typically about 1850 m (1 NM) from the runway threshold), the RTC should be defined/reduced to minimise nuisance alerts.

(d) The RTC values can be reduced slightly for descending flight conditions to accommodate the dynamic conditions and pilot response times.

(e) The FLTA search volume should vary as a function of phase of flight, distance from runway, and the required terrain clearance.

CS ACNS.E.TAWS.020 PDA function requirements

ED Decision 2013/031/R

(See GM1 ACNS.E.TAWS.020)

Provide a Premature Descent Alert function:

(a) to determine if the aeroplane is significantly below the normal approach flight path to a runway and in such a case issue an alert, based on the current position and flight path information of the aeroplane, as determined from a suitable navigation source and airport database;

(b) that is available on all types of instrument approaches including straight-in approaches, circling approaches and approaches that are not aligned within 30 degrees of the runway heading.

GM1 ACNS.E.TAWS.020 PDA function requirements

ED Decision 2013/031/R

The purpose of the PDA alert is to increase pilot’s awareness. Therefore ‘significantly below’ means the point below the profile where the pilot would normally initiate a Go Around (e.g. for ILS this would correspond to 1 dot deviation).

CS ACNS.E.TAWS.025 Class A TAWS inhibition

ED Decision 2013/031/R

(See AMC1 ACNS.E.TAWS.025)

A means is provided to:

(a) the flight crew to inhibit the FLTA and PDA functions together with appropriate annunciation of the inhibited condition. Inhibiting FLTA and PDA does not impact the Basic GPWS functions;

(b) indicate to the flight crew of the ‘Inhibit status’.

AMC1 ACNS.E.TAWS.025 Class A TAWS inhibition

ED Decision 2013/031/R

(a) An automatic inhibit capability is acceptable if it uses the information of the TAWS as a failure monitoring function.             

(b) If an automatic inhibition is provided and it automatically inhibits the FLTA alerts, PDA alerts and terrain display then the manual inhibit may be designed to only inhibit aural and visual alerts.

(c) A separate guarded control should be provided to inhibit GPWS alerts based on flaps being other than the landing configuration.

CS ACNS.E.TAWS.030 Terrain information display

ED Decision 2013/031/R

(See AMC1 ACNS.E.TAWS.030)

(a) When terrain information is provided it is clearly visible to the flight crew.

(b) Terrain information is displayed as follows:

(1) The terrain is depicted relative to the aeroplane’s position such that the pilot may estimate the relative bearing and distance to the terrain of interest.

(2) The terrain depicted is oriented in accordance with the orientation of the navigation information used on the flight deck.

(3) Variations in terrain elevation depicted relative to the aeroplane’s elevation (above and below) are visually distinguishable.

(4) Terrain that generates alerts is displayed in a manner to distinguish it from non-hazardous terrain, consistent with the caution and warning alert level.

(5) If the terrain is presented on a multi-function display, the terrain mode and terrain information is distinguishable from weather and other features.

(6) Terrain information is readily available and displayed with sufficient accuracy and in a manner to allow the flight crew to determine if it is a terrain threat to the aeroplane.

(c) The display of terrain data complements and is compatible with the terrain alerting function of the TAWS.

(d) The terrain information is clear and unambiguous, available without potential confusion during day and night operations under all ambient conditions expected in service.

(e) Where additional terrain views are provided, they must present information consistent and compatible with (a) to (e) above.

AMC1 ACNS.E.TAWS.030 Terrain information display

ED Decision 2022/008/R

(a) Terrain data should be displayed in the maximum field of view. Terrain that is more than 600 m (2000 ft) below the aeroplane’s elevation need not be depicted.

(b) If terrain alerting information is displayed on a weather radar, an Electronic Flight Instrument System display, or other compatible display system available on the flight deck, then the TAWS information should be displayed in a manner consistent with other information (e.g. range, colour coding, symbology).

(c) When Auto-range switching is provided, an auto-ranging display should be designed so that it is evident to the flight crew that the range has been automatically selected. The range selected for auto-ranging should clearly depict the threat on the display. Manual reversion to a selected range should be simple.

[Issue: CS-ACNS/4]

CS ACNS.E.TAWS.035 Aural and visual alerts

ED Decision 2019/011/R

(See AMC1 ACNS.E.TAWS.035)

(a) The TAWS provides suitable aural and visual alerts for each of its functions.

(b) Aural and visual alerts are initiated simultaneously, except when suppression of aural alerts is necessary to protect pilots from nuisance aural alerting.

(c) Each aural alert identifies the reason for the alert.

(d) The system is capable of accepting and processing aeroplane performance related data or aeroplane dynamic data and providing the capability to update aural and visual alerts at least once per second.

(e) The aural and visual outputs are compatible with the standard cockpit displays and auditory systems.

(f) The visual display of alerting information is continuously displayed until the situation is no longer valid.

[Issue: CS-ACNS/2]

AMC1 ACNS.E.TAWS.035 Aural and visual alerts

ED Decision 2019/011/R

(a) The testing of the TAWS system integration within the aircraft should address the provision of the alerts listed in Table 1 below. In addition to this minimum set, other implemented optional voice alerts should be tested.

TABLE 1: Visual and aural alerts

(b) If a two tone sweep (‘Whoop Whoop’) is used then the complete cycle of the two tone sweeps plus annunciation may be extended from ‘1.4’ to ‘2’ seconds.

(c) Note: GPWS alerting thresholds may be adjusted or modified to be more compatible with the FLTA alerting functions and to minimize GPWS nuisance alerts.

(d) Parameters such as airspeed, groundspeed barometric altitude rate should be included in the logic that determines basic GPWS alerting time.

(e) GPWS alerting thresholds may be adjusted or modified to be more compatible with the FLTA alerting functions and to minimize GPWS nuisance alerts.

(f) Consideration should be given to presenting voice announcements at a pre-set level via headsets when they are in use.

[Issue: CS-ACNS/2]