AC 25.1329-1C CHG 2 cause a transient larger than a minor transient . See § 25.1329(c). The transition to the engaged state should be smooth, and should not cause large, unexpected changes in pitch attitudes or pitching moments. The reason for automatic engagement should be clear and obvious to the flightcrew.
Note: The design should consider the possibility that the pilot may attempt to engage the autothrust function outside of the normal flight envelope or at excessive or too low engine thrust. It is not expected that the autothrust feature should compensate for situations outside the normal flight envelope or normal engine operation range, unless that is part of the intended function of the autothrust system.
b. Autothrust disengagement.
(1) Indication of disengagement . Positive indication of disengagement of the autothrust function must result in a caution alert to the flightcrew . See § 25.1329(k). The autothrust “engage” status annunciations should be removed.
(a) Visual indication.
1 Following automatic disengagement: Visual indication of disengagement should persist until canceled by flightcrew action.
2 Following manual disengagement: If an aural alert is provided, visual indication of disengagement should persist for some minimum period. If an aural alert is not provided, visual indication of disengagement should persist until canceled by flightcrew action.
(b) Aural alert. If provided, the aural disengagement alert should be of sufficient duration and volume to assure that the flightcrew has been alerted that disengagement has occurred. However, an extended cycle of an aural alert is not acceptable following disengagement, if such an alert can significantly interfere with flightcrew coordination or radio communication.
(2) Inadvertent disengagement. The autothrust normally should be designed to preclude inadvertent disengagement during activation of autothrust modes of operation.
(3) Consequence of disengagement . Under normal conditions, autothrust disengagement may not cause a transient any greater than a minor transient . See § 25.1329(d).
The transition to the disengaged state should be smooth and not cause unexpected changes in pitch attitude or pitching moment or a significant thrust transient . The disengagement should not preclude, inhibit, or interfere with timely thrust changes for go-around, landing, or other maneuvers requiring manual thrust changes.
(4) Autothrust quick disengagement control . Autothrust quick disengagement controls must be provided for each pilot on the respective thrust control (thrust lever or equivalent). A single-action, quick disengagement switch must be incorporated on the thrust control, so that switch activation can be executed when the pilot’s other hand is on the control wheel (or equivalent). See § 25.1329(a). The disengagement control should be positioned such 20
AC 25.1329-1C CHG 2 that inadvertent disengagement of the autothrust function is unlikely. Positioning the control on the outboard side has been shown to be acceptable for multi -engine aircraft. Thrust lever knob, end-mounted disengagement controls available on both sides to facilitate use by either pilot have been shown to be preferable to those positioned to be accessible by the pilot’s palm.
30. Override of the FGS.
a. General. An override of an engaged FGS function is defined as an action taken by the flightcrew intended to prevent, oppose, or alter an operation being conducted by the FGS function without first disengaging that function.
b. Autopilot override.
(1) With automatic disengagement.
(a) Override force. The autopilot should disengage when the flightcrew applies a significant override force to the controls . The applicant should interpret “significant” as a force that is consistent with an intention to overpower the autopilot by either or both pilots. The autopilot should not disengage by minor application of force to the controls, such as a pilot gently bumping the control column while entering or exiting a pilot seat during cruise.
Note: Twenty-five pounds (25 lbs) of force at the control column or wheel has been determined to be a significant override force level for other than approach operations on some aircraft types. To reduce nuisance disengagement, higher forces have been found acceptable for certain approach, landing, and go -around operations on some aircraft. The force to disengage an autopilot is not necessarily the force required at the column to oppose autopilot control, that is, to cause elevator movement . The corresponding forces for a sidestick controller may be diff erent.
(b) Transients resulting from override. In normal operating conditions, a transient larger than a minor transient may not result from autopilot disengagement when the flightcrew applies an override force to the controls . See § 25.1329(d). Mitigation may be accomplished through provision of an appropriate alert and flightcrew procedure.
(c) Sustained override force below level required for automatic disconnect .
Sustained application of force below the disengagement threshold may not result in a potential hazard. See § 25.1329(l). For example, the automatic trim should not run to oppose the override of the autopilot by the flightcrew that would result in unacceptable airplane motion, if the autopilot were to automatically disengage or be manually disengaged.
AC 25.1329-1C CHG 2
(2) Without automatic disengagement.
(a) Potential hazard. If the FGS is not designed to disengage in response to any override force, then the response to an override may not result in a potential hazard. Sustained application of an override force may not result in a potential hazard, such as when the flightcrew abruptly releases the force on the controls. See § 25.1329(l). Mitigation of the potential hazard may be accomplished through provision of an appropriate alert and flightcrew procedure. During sustained application of an override force, the automatic trim should not run to oppose the flightcrew commands in any manner that would result in unacceptable airplane motion.
Note: The term “sustained application of override force” is intended to describe a force that is applied to the controls , which may be small, slow, and sustained for some period of time . This may be due to an inadvertent crew action or may be an intentional crew action meant to “assist” the autopilot in a particular maneuver. (See Chapter 9, Compliance Demonstration Using Flight Test and Simulation, paragraph 99.f, Flightcrew Override of the FGS, of this AC for more information.)
(b) Transients resulting from override. In normal operating conditions, a transient larger than a minor transient may not result from manual autopilot disengagement after the flightcrew has applied an override force to the controls . See § 25.1329(d). Mitigation may be accomplished through provision of an appropriate alert and flightcrew procedure.
Note 1: The term “override force” is intended to describe a pilot action that is intended to prevent, oppose , or alter an operation being conducted by a flight guidance function without first disengaging that function. One possible reason for this action could be an avoidance maneuver, such as responding to a traffic alert and collision avoidance system (TCAS) resolution advisory that requires immediate action by the flightcrew and would typically involve a rapid and forceful input from the flightcrew.
Note 2: For control wheel steering considerations, see Chapter 6 , Characteristics of Specific Modes , paragraph 68, Control Wheel Steering (Control Steering through the Autopilot) , of this AC.
c. Autothrust override.
(1) Force required. It should be possible for the pilot to readily override the autothrust function and set thrust by moving the thrust levers (or equivalent) with one hand.
(2) Response to override. The autothrust response to a flightcrew override may not create a potential hazard . See § 25.1329(m). The autothrust response to the flightcrew override should not result in an abrupt change of pitch attitude, an abrupt pitching moment, or an uncontrolled change of thrust.
AC 25.1329-1C CHG 2
(3) Engagement status with override. Autothrust functions may be designed to remain safely engaged during pilot override . Alternatively, autothrust functions may disengage as a result of pilot override, provided that the design prevents unintentional autothrust disengagement and adequately alerts the flightcrew to ensure pilot awareness.
31. FGS Engagement Mode Compatibility.
a. FGS mode engagement philosophy. A description of the philosophy used for the mode at engagement of the autopilot, FD, and autothrust functions should be provided in flightcrew training material.
b. Engagement mode compatibility. It should not be possible to select incompatible FGS command or guidance functions, such as commanding speed through elevator and autothrust at the same time. The FGS command or guidance functions should also not allow engagement by flightcrew selection, or automatic transition during a failure, into incompatible or unintended modes of operation, or a mode inappropriate for the phase of flight that may result in a potential hazard (ex., ALT pitch mode for takeoff). The hazard resulting from unintended mode transitions due to failures should be assessed in accordance with the requirements of § 25.1309.
32—41 [RESERVED] 23
CHAPTE R 4. CONTROLS, INDICATIONS, AND ALERTS
42. General.
a. Human-machine interface (HMI). The HMI with the FGS is crucial to ensuring safe, effective, and consistent FGS operation . The manner in which FGS information is depicted to the flightcrew is vital to flightcrew awareness and, therefore, to safe operation of the FGS.
b. Design of controls, indications, and alerts. These features must be designed to minimize flightcrew errors and confusion. See § 25.1329(i). Indications and alerts should be presented in a manner compatible with the procedures and assigned tasks of the flightcrew and provide the necessary information to perform those tasks . The indications must be grouped and presented in a logical and consistent manner and must be visible from each pilot’s station under all expected lighting conditions . See § 25.1329(i). The choice of colors, fonts, font size, location, orientation, movement, graphical layout, and other characteristics —such as steady or flashing— should all contribute to the effectiveness of the system. Controls, indications, and alerts should be implemented in a consistent manner.
c. Evaluation of information provided by FGS. It is recommended that the applicant evaluate the adequacy and effectiveness of the information provided by the FGS interface —that is, the controls, indications, alerts, and displays —to ensure flightcrew awareness of FGS behavior and operation. See Chapter 9 of this AC for more discussion of appropriate analyses , which may include, for example, cognitive task analysis as a basis for evaluation.
43. FGS Controls.
a. General. The FGS controls must be designed and located to prevent crew errors, confusion, and inadvertent operation. See § 25.1329(i). They should be designed to provide convenience of operation to each crewmember . The function and direction of motion of each control must be readily apparent or plainly indicated on or adjacent to each control, if needed to prevent inappropriate use or confusion. See § 25.1329(f). Sections 25.777(b) and 25.779(a) provide requirements regarding direction of motion of flight deck controls . These requirements apply for FGS command reference controls that select target values, such as heading select or vertical speed. Section 25.781 also provides requirements for the shapes of the knobs.
b. Design considerations. The design of the FGS should address the fol lowing specific considerations:
(1) Differentiation of knob shape and position. Errors by the flightcrew have included confusing speed and heading knobs on the MSP.
(2) Design to support correct selection of target values. Use of a single control, such as concentric controls, for selecting multiple command reference targets has resulted in erroneous target value selection.
(3) Commonality across aircraft types. Use of uniform control design in different aircraft prevents negative transfer of learning with respect to operation of the controls . Using knowledge about the operation of the controls on one type of airplane has resulted in activation of the incorrect control when pilots move d from that type of airplane to another type of airplane .
An example of this is confusion between the takeoff/go- around (TOGA) button and the autothrust disengagement button when transitioning between aircraft types with differing designs and locations for these controls.
(4) Positioning of controls and related indications. Individual FGS controls, flight mode annunciator (FMA), and related PFD information should be positioned so that, as much as reasonably practical, items of related function have similarly related positions . Misinterpretation and confusion have occurred due to the inconsistent arrangement of FGS controls with the annunciations on the FMA.
(5) Inadvertent operation. The FGS controls must be located to discourage or avoid inadvertent operation, such as inadvertent engagement or disengagement . See § 25.777(a).
Further design aspects of the FGS controls, other than location of the controls, should also be used to discourage or avoid inadvertent operation. Examples include the shape of the control and the force required for operation.
44. FGS Mode Selection, Annunciation, and Indication.
a. Annunciation of engagement of the FGS. Engagement of the FGS functions must be suitably annunciated to each pilot . See § 25.1329(i). Guidance is provided in Chapter 3, FGS Engagement, Disengagement, Indications, and Override, of this AC.
b. Description of FGS modes. The operator should be provided with appropriate descriptions of the FGS modes and their behaviors.
c. FGS mode annunciations. Mode annunciation must indicate the state of the system.
See § 25.1329(i). Mode annunciation should be presented in a manner compatible with flightcrew procedures/tasks and be consistent with the mode annunciation design for the specific aircraft type. That is, the mode annunciation should be compatible with other flight deck systems mode annunciations. Mode selector switch position or status is not acceptable as the sole means of mode annunciation. See § 25.1329(i). Modes and mode changes should be depicted in a manner that achieves flightcrew attention and awareness.
(1) Active and armed modes. The FGS mode annunciations must effectively and unambiguously indicate the active and armed modes of operation. See § 25.1329(i). The mode annunciation should convey explicitly, and as simply as possible, what the FGS is doing (for active modes), what it will be doing (for armed modes), and target information (such as selected speed, heading, and altitude) for satisfactory flightcrew awareness.
(2) Location. Mode annunciations should be located in the forward field of view . For example, a suitable location is on the PFD . Engaged modes should be annunciated at different locations than armed modes to assist in mode recognition.
AC 25.1329-1C CHG 2
(3) Discriminators. Color, font type, font size, location, highlighting, and symbol flashing have historical precedent as good discriminators, when implemented appropriately. The fonts and font size should be chosen so that annunciation of FGS mode and status information is readable and understandable without eyestrain when viewed by the pilot seated at the design eye position. The use of graphical or symbolic (that is, non-textual) indications is acceptable .
Implementation of such discriminators should follow accepted guidelines, as described in applicable international standards (such as AC 25-11B, Electronic Flight Displays), and should be evaluated for their consistency and integration with the flight deck design.
(4) Color. Color should be used in a consistent manner and assure compatibility with the overall use of color on the flight deck. Specific colors should be used such that the FGS displays are consistent with other flight deck systems, such as a FMS . The use of monochrome displays is not precluded, provided that the aspects of flightcrew attention and awareness are satisfied. Engaged modes should be annunciated with different colors than armed modes to assist in mode recognition.
d. Mode changes.
(1) Operationally relevant mode changes. Mode changes that are operationally relevant—especially mode reversions and s ustained speed protection—should be clearly and positively annunciated to ensure f lightcrew awareness. Altitude Capture is an example of an ope rationally relevant mode that should be ann unciated because pilot actions duri ng that br ief time the mode is operational may ha ve d ifferent effects on th e airplane. Annunciation of sustained speed protection should be c lear and distinct to ensure flightcrew awareness. The FGS sub-mo des that are not operationally relevant (f or example, sub-modes as the FGS transitions from instrument la nding system L ocalizer (LOC) Capture to Localizer Track) need not be annunciated.
(2) Attention-getting features. The transition from an ar med mode to an engaged mode should provide an a dditional a ttention-getting feature, such as boxing and flashing on an el ectronic display (see AC 25-11B) for a suitable, but brief, period (for example, 10 seconds) to as sist in fl ightcrew aw areness. Aural notification of mode changes should be limited to special considerations.
(3) Use of alerts. In-service expe rience has shown that mode annunciation alone ma y be insufficient—unc lear or not compelling enough—to communicate mo de changes to th e flightcrew, especially in high workload situations . Therefore, the safety con sequences of the fl ightcrew not recognizing mode changes should be cons idered. If necessary, an appropriate alert shou ld be used.
e . Failure to engage or ar m . The failure of a mode to e ngage or a rm when selected by the pilot should be apparent.
f. FGS mode di splay and i n dications . Mode information provided to the f lightcrew s hould be sufficiently detailed, so that the cons equences of t he interaction between the FG S and the flightcrew can be determined unambiguously. The FGS interface should provide timely and 26
AC 25.1329-1C CHG 2 positive indication when the FGS deviates from the pilot’s direct commands (for example, a target altitude or speed setting) or from the pilot’s pre-programmed set of commands (for example, waypoint crossing). The interface should also provide clear indication when there is a difference or conflict between pilot-initiated commands. An example would be when a pilot engages positive vertical speed and then selects an altitude that is lower than the aircraft altitude.
The default action taken by the FGS should be made apparent.
45. FGS Alerting, Warning, Caution, Advisory, and Status .
a. General.
(1) Alerting provisions. Alerting information must follow the provisions of § 25.1322.
The advisory material associated with § 25.1322 should be consulted. Alerts for FGS engagement and disengagement are described in Chapter 3 of this AC.
(2) Determination of FGS capability. There should be some method for the flightcrew to determine and monitor the availability or capability of the FGS (for example, prior to dispatch), where the intended operation is predicated on the use of the FGS . The method of monitoring provided should take into account the hazard resulting from the loss of the autopilot function for the intended operation.
b. Speed protection alerts.
(1) Alerts to crew. To assure crew awareness, an alert should be provided when a sustained speed protection condition is detected. This is in addition to any annunciations associated with mode reversions that occur as a consequence of invoking speed protection. (See Chapter 5, paragraph 57, Speed Protection, of this AC).
(2) Alert specifications.
(a) Low-speed protection. Low-speed protection alerts should include both an aural and a visual component.
(b) High-speed protection. High-speed protection alerts need include only a visual alert component because of existing high-speed aural alert requirements . However, giving an alert prior to that required aural alert is not precluded . See § 25.1303(c)(1) for overspeed alerting regulations.
(3) Consistency. Alerts for speed protection should be consistent with the protection provided and with the other alerts in the flight deck.
(4) Nuisance alerts. Care should be taken to set appropriate values for indicating speed protection that would not be considered a nuisance for the flightcrew.
c. Loss of autopilot Approach mode. The loss of the Approach mode requires immediate flightcrew awareness. This may be accomplished through autopilot di sengagement described in this AC and AC 20-191. If the autopilot remains engaged and reverts to a non -approach mode, an appropriate aural and/or visual alert should be provided.
10/27/14 A C 25.1329-1C
d. Awareness of potential significant transient condition (“b ark before bite”).
(1) General. There have been situations where an autopilot was engaged, operati ng n ormally, and controlling up to the limit of its authority for an extended period of time, and the flightcrew was unaware of the potential hazard . This service experience has shown that, without timely flightcrew awareness and action, such a situation can progress to a loss of control after autopilot disengagement, particularly in rare normal or non-normal conditions . However, with adequate flightcrew awareness and pilot action, l oss of control may be prevented.
(2) Flightcrew alert(s). To help ensure flightcrew awareness and timely action, appropriate alert(s)—normally a caution or warning—should be provided to the flightcrew for conditions that could require exceptional piloting skill or alertness for manual control following autopilot disengagement (for example, significantly out -of-trim conditions). The number and type of alerts required should be determined by the unique situations that are being detected and by the crew procedures required to address those situat ions. Any alert should be clear and unambiguous and should be consistent and compatible with other flight deck alerts . Care should be taken to set appropriate thresholds for these alerts so that they are not considered a nuisance for the flightcrew.
(3) Situations to consider for an alert.
(a) Sustained lateral control command. If the autopilot is holding a sustaine d l ateral control command, it could be indicative of an unusual operating condition for which the autopilot is compensating. Examples of such unusual operating conditions are asymmetric lift and/or drag due to asymmetric icing, fuel imbalance, or asymmetric thrust . In the worst case, the autopilot may be operating at or near its full authority in one direction. If the autopilot were to disengage while holding this lateral trim, the result would be that the airplane could undergo a rolling moment that could possibly take the pilot by surprise . Therefore, a timely alert should be considered to permit the crew to manually disengage the autopilot and take control prior to any automatic disengagement that might result from the condition.
(b) Sustained pitch command. If the autopilot is holding sustained pitch command, it could be indicative of an unusual operating condition (for example, inoperative automatic horizontal trim) for which the autopilot is compensating. If the autopilot were to disengage while holding this pitch command, the result would be that the airplane could undergo an abrupt change in pitch that could possibly take the pilot by surprise . Therefore, a timely alert should be considered to permit the crew to manually disengage the autopilot and take control prior to any automatic disengagement that might result from the condition.
(c) Bank and pitch angles. Most autopilots are designed with operational limits in both the pitch and roll axes, such that those predetermined limits will not be purposely exceeded.
If the airplane exceeds those limits, it could be indicative of a situation that requires the pilot to intervene. Such a situation may not be covered by paragraphs 45.d(3)(a) or 45.d(3)(b) above.
Therefore, a timely alert should bring this condition to the attention of the flightcrew and permit the crew to manually disengage the autopilot and take control prior to any automatic disengagement that might result.
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(4) Automatic disengagement. It is preferable that the autopilot remains engage d dur ing out-of-trim conditions. However, if there is an automatic disengagement feature due to excessive out-of-trim, an alert should be generated and should precede any automatic disengagement with sufficient margin to permit timely flightcrew recognition and manual disengagement. See also Chapter 3, paragraph 30, Override of the FGS, of this AC for related material.
Note 1: This paragraph is not intended to require alerting for all instances of automatic autopilot disengagement . It is intended only for conditions that would, if not addressed, lead to disengagement that could result in a significant transient (or greater) for which the pilot may be unprepared. The intent is to provide crew awareness that would allow the flightcrew to be prepared with hands on controls and take appropriate corrective action before the condition results in a potentially hazardous airplane configuration or state.
Note 2: This paragraph describes alerting requirements for conditions resulting in unintended out-of-trim operation. There are FGS functions that can intentionally produce out-of-trim conditions. Examples would be parallel rudder operation in align or engine failure compensation modes, pitch trim operation during the approach/landing to provide trim up/flare spring bias, and pitch trim operation for certain types of speed/Mach trim systems . It is not the intent of this paragraph to require alerts for functions producing intentional out -of-trim conditions. Other system indications (for example, mode and status annunciations) should be provided to make the crew aware of the operation of these functions, where appropriate.
46. FGS Considerations for HUDs.
a. General. HUDs have unique characteristics compared to flight displays installed on the instrument panel. Most of these HUD differences are addressed during HUD certification , whether or not the HUD provides flight guidance functions . The intent of this chapter is to address how such HUD differences may affect FGS functions . (See SAE ARP5288 for further information on this subject . See paragraph 4.c of this AC for information on how to obtain SAE documents.)
b. Characteristics of HUD guidance.
(1) Supplemental use display system. If the HUD is designed as a supplemental use display system, it does not replace the requirement for standard head down display (HDD) of flight instrument data. The HUD is intended for use during takeoff, climb, cruise, descent, approach, and landing under day, night, visual meteorological conditions (VMC), and instrument meteorological conditions (IMC). When it can be reasonably expected that the pilot will operate primarily by reference to the HUD, it should be shown that the HUD is satisfactory for manually controlling the airplane and for monitoring the performance of the FGS.
(2) External visual references. During takeoff and landing in certain light a nd vi sibility conditions, HUD symbology can be extremely dominant in comparison to external 29
10/27/14 A C 25.1329-1C 30 visual references. When visual references are relatively dim, extremely active symbology dynamics and guidance cue gains can lead the pilot to make excessively strong corrections . It should be shown that—if HUD guidance cues are followed regardless of the appearance of external visual references—they do not cause the pilot to take unsafe actions.
(3) Interference and occlusion. It should be shown that there is no interference between the indications of primary flight information and the flight guidance cues . In takeoff, approach, and landing FGS modes, the flight guidance symbology should have occlusion priority. That is, the flight guidance symbology should not be obscured or covered by the primary flight information. The HUD guidance symbology should not excessively interfere with pilots’ forward view, ability to visually maneuver the airplane, acquire opposing traffic, and see the runway environment.
(4) Display criteria. Generally, the criteria for the mechanization of guidanc e di splayed on the HUD should be no different than for guidance displayed on the HDD. See Chapter 5 of this AC.
(5) Conformal symbology. Unlike HDDs, HUDs are capable of displaying certain symbology conformal to the outside scene, including guidance cues . Consequently, the range of motion of this conformal symbology, including the guidance cues, can present certain challenges in rapidly changing and high crosswind conditions . In certain cases, the motion of the guidance and the primary reference cue may be limited by the field of view . It should be shown that, in such cases, the guidance remains usable and that there is a positive indication that it is no longer conformal with the outside scene.
(6) Low-visibility approach. The HUD guidance is often used in cases, like the low - visibility approach, where the pilot will need to reference both the information displayed on the HUD and outside references . Consequently, it should be shown that the location and presentation of the HUD information does not distract the pilot or obscure the pilot’s outside view . For example, it would be necessary for the pilot to track the guidance to the runway without having the view of runway references or hazards along the flight path obscured by the HUD symbology.
(7) Clutter. The HUD display should present flight guidance information in a clear and unambiguous manner. Display clutter should be minimized . Some flight guidance data elements are essential or critical and should not be remo ved by any de-clutter function.
c. HUD/HDD compatibility.
(1) General. The HUD FGS symbology should be compatible and consistent wit h s ymbology on other FGS displays such as head down electronic flight instruments. The FGS-related display parameters should be consistent to avoid misinterpretation of similar information, but the display presentations need not be identical . The HUD and head down PFD formats and data sources need to be compatible to ensure that the same FGS -related information presented on both displays h ave the same intended meaning.
(2) Consistency and compatibility. While not all information displayed on the HUD is directly related to the FGS, the pilot is likely to use most of the displayed information while using the HUD-displayed guidance and FGS annunciations . Therefore, when applicable, the
AC 25.1329-1C CHG 2 guidelines below for the presentation of FGS -related display information should be followed as much as possible. Certain deviations from these guidelines may be appropriate due to conflict with other information display characteristics or requirements unique to HUDs . These may include minimization of display clutter, minimization of excessive symbol flashing, and the presentation of certain information conformal to the outside scene.
(a) Symbology. Symbols should be the same format. For example, a triangle-shaped pointer head down should appear as a triangle pointer head up. However, some differences in HUD symbology, such as the FD “circle” versus head down FD “bars” or “wedge,” have been found acceptable.
(b) Location. Information (symbols) should appear in the same general location relative to other information.
(c) Alphanumeric data. Alphanumeric readouts should have the same resolution, units, and labeling. For example, the command reference indication for “vertical speed” should be displayed in the same foot-per-minute increments and be labeled with the same characters as the HDDs.
(d) Analog scales. Analog scales or dials should have the same range and dynamic operation. For example, a glideslope deviation scale displayed head up should have the same displayed range as the glideslope deviation scale displayed head down, and the direction of movement should be consistent.
(e) Display of FGS modes. The FGS modes and status state transitions should be displayed on the HUD using consistent methods, except for the use of color . That is, the method used head down to indicate a FD mode transitioning from armed to captured should also be used head up.
(f) Information sources. Information sources should be consistent between the HUDs and the HDDs used by the same pilot.
(g) Display of FGS command information. When FGS command information (for example, a FD command) is displayed on the HUD in addition to the HDDs, the HUD depiction and guidance cue deviation “scaling” needs to be consistent with that used on the HDDs . This is intended to provide comparable pilot performance and workload when using either HUDs or HDDs.
(h) Display for pilot monitoring (PM). The same information concerning current HUD system mode, reference data, status state transitions, and alert information that is displayed to the pilot flying (PF) on the HUD should also be displayed to the PM on the HDDs. Consistent nomenclature should be used to ensure unambiguous awareness of the HUD operation.
d. Alerting issues.
(1) Alerts displayed on HUDs. Although HUDs are typically not intended to be classified as integrated caution and warning systems, they may display cautions, warnings, and 31