CS AWO.A.HUD.109 Head-up display landing systems
ED Decision 2022/007/R
For HUDLSs that are used for primary guidance (HUD manual landing) during Category III operations (see Subpart B Section 4), the following are required:
(a) System failure conditions that result in the inability to complete the landing from the DH until touchdown using the HUDLS shall not have a frequency of occurrence of more than once every thousand approaches.
(b) In the event of an engine failure, the HUDLS shall permit the pilot to control the aeroplane without reverting to other displays.
(c) Alignment should not be significantly affected in normal operation between scheduled maintenance activities.
[Issue: CS-AWO/2]
CS AWO.A.HUD.110 Head-up displays used for enhanced flight vision systems
ED Decision 2022/007/R
(a) HUDs (or equivalent displays) used to display enhanced flight vision system (EFVS) imagery shall have a field of regard (FOR) that is appropriate to the intended usage (see CS AWO.A.EFVS.104(b), (c) and (d)).
(b) Where the EFVS image is superimposed on the HUD (or equivalent display) symbology, then the EFVS image and installation shall, in the absence of any failure:
(1) satisfactorily perform its intended function;
(2) permit the accurate identification and utilisation of visual references, using both EFVS and natural vision, as appropriate;
(3) have acceptable display characteristics to accomplish the intended function;
(4) not degrade the presentation of essential flight information listed in CS AWO.A.EFVS.105(a) on the HUD (or equivalent display);
(5) not be misleading and not cause confusion nor any significant increase in pilot workload;
(6) be aligned with and scaled to the external scene, and consider, if needed, the effect of parallax;
(7) not alter the colour perception of the external scene in ways that cause confusion, significantly increase pilot workload, or prevent the pilot from performing any required tasks (e.g. discerning precision approach path indicators (PAPIs));
(8) permit the pilot to recognise misaligned or non-conformal conditions to the external scene that may preclude the pilot’s performance of any required manoeuvres;
Note: The misalignment or non-conformal conditions shall be those that can be detected by the system.
(9) provide a means to control the EFVS scene brightness that is independent of the HUD (or equivalent display) symbology brightness control; this control shall be operable without causing excessive pilot workload, and not cause adverse physiological effects such as fatigue or eye strain;
(10) provide a readily accessible control to enable the pilot to remove and reactivate the EFVS image from the HUD (or equivalent display) without requiring the pilot to remove their hands from the primary flight controls and thrust control.
[Issue: CS-AWO/2]
CS AWO.A.HUD.111 Head-up displays used for synthetic vision guidance systems
ED Decision 2022/007/R
A HUD (or equivalent display) used in a synthetic vision guidance system (SVGS) shall:
(a) provide a means to control the SVGS scene brightness that is independent of the HUD (or equivalent display) symbology brightness control; this control shall be operable without causing excessive pilot workload, distraction or fatigue;
(b) provide a readily accessible control to enable the pilot to remove and reactivate the SVGS image from the HUD (or equivalent display) without requiring the pilot to remove their hands from the primary flight controls and thrust control;
(c) not cause interference with the safe and effective use of the pilot compartment view, either internally or externally;
(d) not cause adverse physiological effects to the pilots, such as fatigue or eye strain;
(e) not significantly alter the colour perception of the external scene;
(f) allow the pilot to recognise misaligned or non-conformal conditions in a timely manner; and
(g) not create a combination of display features to the extent that display clutter reduces the efficiency of reading and interpreting the pilot’s external visual cues.
If found to be necessary, a means to control the SVGS scene contrast shall be provided.
Note: In point (f), the misalignment or non-conformal conditions shall be those that can be detected by the system.
[Issue: CS-AWO/2]
CS AWO.A.HUD.112 Head-up display landing distance
ED Decision 2022/007/R
If there is any feature of the HUD (e.g. flare cue) or the associated procedures intended to support the flare manoeuvre for landing which would result in an increase to the landing distance, the appropriate increment shall be established and scheduled in the AFM.
[Issue 2: CS-AWO/2]
AMC AWO.A.HUD.112 HUD landing distance
ED Decision 2022/007/R
(a) The following definitions should apply when considering the concept of a flare cue:
(1) ‘flare cue’: a flare cue is specific symbology displayed on the HUD that supports the flare manoeuvre; for this purpose, a flare cue may be implemented as a ‘flare prompt’ or ‘flare guidance’.
(2) ‘flare prompt’: a flare prompt advises the pilot when it is time to initiate the control inputs for the flare manoeuvre and transition to landing; a flare prompt should not provide command guidance for manoeuvring the aeroplane with regard to the rate or magnitude of manual inputs, alignment to runway heading nor touching down at a specific point on the runway.
(3) ‘flare guidance’: provides explicit command guidance for the pilot to flare the aircraft from the initiation of the manoeuvre until touchdown.
(b) The term ‘flare cue’ is used in this AMC as a general term that describes either a ‘flare prompt’ or ‘flare guidance’.
(c) The determination of the landing distance when using a HUD or equivalent display should be performed when one of the following features are part of the intended design:
(1) flare guidance;
(2) a flare prompt in combination with flare guidance; or
(3) a flare prompt, if the height at which the flare is prompted differs from the one at which the landings without using the HUD or equivalent display are performed to the extent that it could have an impact on the landing distance.
(d) A flare cue provided on a HUD or equivalent display is typically provided in the vertical axis by means of a symbol that prompts the pilot to initiate the flare at a suitable moment, and can guide the pilot to control the vertical flight path to touchdown.
(e) For a HUD or equivalent display that is used for landing and designed to provide display features such as a flare cue to support the pilot’s task of executing the landing:
(1) The landing distance assessment should cover all the conditions scheduled in the AFM, including landing in abnormal conditions and, if applicable, specific operations.
(2) The requirements of CS 25.125 should be applied, except that the configuration, procedure and speed should be those recommended in the associated procedures for using a HUD or equivalent display.
(3) The operating procedures, aeroplane configuration, approach speed, thrust management, piloting techniques and the landing distance data applicable for landings using a HUD or equivalent display with a flare cue should be furnished in the AFM.
(4) The landing distance as derived under (e)(2) should be compared with the landing distance determined without the flare cue (unfactored landing distance as per CS 25.125):
(i) If the landing distance using the flare cue is longer than without it, the unfactored landing distance with flare cue is the one derived under (e)(2).
(ii) If the landing distance is the same (flare cue does not modify the air time and speed reduction), then the unfactored landing distance with flare cue is equal to the landing distance established in accordance with CS 25.125. A minimum factor to be applied to the unfactored landing distance with flare cue should be determined to account for the difference between:
(A) the flight path angle used in the analysis for compliance with the specifications of CS 25.125 and that which is used for the flare cue (typically –3.0°);
(B) the touchdown sink rate used in the analysis for compliance with the specifications of CS 25.125 and the one as per the intended design of the flare cue.
The AFM should provide the unfactored landing distance with the flare cue and the minimum factor as determined above.
(iii) In any case, the landing distance may not be shorter than the landing distance established in accordance with CS 25.125 without using the flare cue.
[Issue 2: CS-AWO/2]
CS AWO.A.HUD.113 Flare cue performance
ED Decision 2022/007/R
(a) The use of the flare cue must provide for acceptable performance in all conditions for which it is intended to be used.
(b) The use of flare cue should not require exceptional piloting skill, alertness, strength nor induce excessive pilot workload.
[Issue 2: CS-AWO/2]
AMC1 AWO.A.HUD.113 Criteria for acceptable landing performance using a flare cue
ED Decision 2022/007/R
(a) The use of the flare cue during specific operations (e.g. steep approach, if approved) and abnormal conditions should be evaluated unless the AFM prohibits the use of the flare cue during those operations and/or abnormal conditions. The AFM should explicitly state whether there are cases when the flare cue cannot be used.
(b) Acceptable performance using a flare cue is achieved when the following criteria are demonstrated by flight test:
(1) touchdown is achieved within the touchdown zone, which is the first one third, or the first 3 000 ft, of the usable runway, whichever is more restrictive;
(2) the average touchdown sink rate does not exceed 6 ft per second;
(3) touchdown with a bank angle that it is not hazardous to the aeroplane (i.e. no contact of any part of the engine nacelle or the wing with the ground).
A safe go-around is possible at any time including touchdown in all configurations to be certified.
(c) The flare, from initiation until touchdown, should be assessed to ensure the following:
(1) Suitable flare performance that ensures the following:
(i) no evidence of early or late flare;
(ii) no over-flare or under-flare;
(iii) no undue ‘pitch-down’ tendency at flare initiation or during the flare;
(iv) no flare oscillation;
(v) no abrupt flare;
(vi) no inappropriate pitch response during the flare;
(vii) no unacceptable floating tendency;
(viii) any other unacceptable characteristic that a pilot could interpret as failure or inappropriate response of the flight guidance system, and disconnect, disregard, or contradict the flare indication.
(2) For a nominal range of 2.5 to 3.5° approach paths, demonstrate that there is not a substantial reduction in the flare performance from 2.0 to 4.0°.
[Issue 2: CS-AWO/2]
AMC2 AWO.A.HUD.113 Conditions for the demonstration of an acceptable landing with flare cue
ED Decision 2022/007/R
(a) In accordance with CS AWO.HUD.113, the use of a flare cue during landing should ensure that the landing performance is acceptable according to the criteria established in AMC1 AWO.A.HUD.113 for all normal conditions where it is intended to be certified, which should include at least the following:
(1) landing weight range and centre-of-gravity (CG) range;
(2) range of speed, including possible aircraft failure cases for which flare cue is still intended to be used;
(3) tailwind;
(4) crosswind;
(5) turbulence;
(6) sensor (e.g. radio altimeter, vertical speed) nominal accuracy;
(7) runway slope and runway slope changes in touchdown zone;
(8) final approach angle;
(9) irregular terrain before to runway threshold.
(b) Appropriate limitations on the use of the flare cue in relation to the conditions that it can be used should be published in the AFM.
[Issue: CS-AWO/2]
CS AWO.A.HUD.114 Assessment of the failure conditions relating to the use of flare cues
ED Decision 2022/007/R
An assessment of the effects of failure conditions relating to the use of the flare cue shall be conducted in accordance with CS 25.1309.
[Issue 2: CS-AWO/2]
AMC AWO.A.HUD.114 Assessment of the failure conditions associated with the use of the flare cue
ED Decision 2022/007/R
(a) For the purpose of the failure assessment of the flare cue in the context of CS 25.1309, it may be necessary to use a simulator with an acceptable visual system, which accurately represents the real aeroplane, in particular the handling qualities, the ground effect, the fog structure, and the cut-off angle (i.e. the angle between the longitudinal axis of the aircraft and an incline plane below up to the limit at which the pilot can view).
(b) The failure assessment of the flare cue should take into account at least the following nominal environmental conditions:
(1) minimum visibility / RVR of the operation intended to be certified (e.g. RVR 550m for CAT I,
RVR 300m for EFVS-L);
(2) day and night conditions;
(3) runways with different length and width;
(4) runways with different lighting layout (e.g. no centre line lights, no TDZ lights, etc.).
(c) As flare cue failures are expected to be detected by the flight crew using visual cues, a multiple representative population range of flight crews should be involved in the failure assessment of the flare cue in the simulator.
[Issue 2: CS-AWO/2]