AC 25.1329-1C CHG 2 paragraph 100.b, Validation Elements, of this AC. The failure condition should be inserted at a safe but representative height . The deviation profile should be identified and applied as indicated in AC 25-7D, paragraph 33.7.10.5, Approach.
(1) Approach with vertical path reference.
(a) xLS (that is, ILS or GLS).
1 ILS operations are typically conducted on instrument approach procedures designed in accordance with United States Standard for Terminal Instrument Procedures (TERPS). See FAA Order 8260.3B, or the International Civil Aviation Organization (ICAO) Procedures for Air Navigat ion Services—Aircraft Operations (PANS-OPS) criteria or equivalent. These criteria, together with ICAO Annex 14, are generally intended to take into account obstacles beneath a reference obstacle identification surface.
Note: The FAA may establish operational criteria for GLS at a later time.
2 In assessing the implication of the effect of failures during autopilot operations, a reference 1:29 slope penetration boundary has been applied against the deviation profile to identify an appropriate altitude for continued autopilot operation. The 1:29 slope has been found to provide an acceptable margin above obstacles on an approach.
3 The worst-case failure condition identified by the safety assessment (see Chapter 8, paragraph 87, Validation of Failure Conditions ) should be demonstrated against the deviation profile criteria and a MUH should be established . (See AC 25-7D, paragraph 33.7.10.5.3, Assessment of Approach with Vertical Path Reference .)
(b) Area navigation.
1 For RNAV coupled approach operations, a vertical flight path similar to an xLS flight path will be used (for example, 3 degree path starting 50 feet above the threshold).
However, due to sensor characteristics it is assumed that RNAV operations will be conducted with a DA(H) or MDA(H) that is higher than an equivalent MUH on an xLS approach to the same runway. Further, for this type of operation, it should be noted that the MUH is always in the visual segment of the approach, as the failure recognition and recovery maneuver are assumed to be conducted with the pilot having established outside vi sual reference.
2 In order to derive only one MUH value for simplicity of use, it is assumed that the effects of failure on the autopilot in RNAV operation are no worse than for the xLS operation. No further determination or demonstration is required. However, the applicant should show that due account has been taken in the safety assessment of the differences between the RNAV and xLS inputs to the autopilot (for example, barometric altitude input, FMS position and guidance commands, and their failure e ffects). If these effects can be bounded or otherwise reconciled, then the xLS demonstrated MUH may also be considered applicable to RNAV operations.
AC 25.1329-1C CHG 2 3 If these effects cannot be bounded or accounted for within those for the xLS operation, the MUH should be determined in accordance with an Approach w ithout Vertical Path Reference below.
(2) Approach without vertical path reference. For an approach without vertical path reference (for example, VOR, Non Directional Beacon ( NDB), localizer only) the FGS mode of operation is typically vertical speed/flight path angle (that is, a cruise mode). The worst-case failure condition for this type of mode should be demonstrated in the approach configuration. An appropriate height loss should then be established in accordance with the method described in AC 25-7D, paragraph 33.7.10.5.4.
(3) Steep approach. In support of an approval to use the FGS on glidepath angles of greater than 3.77 degrees (see Chapter 9, paragraph 99.d(5), Steep Approach (Special Authorization) of this AC), an assessment should be made of the effects of failure conditions for this type of operation. For use of autopilot, an appropriate MUH should be established in accordance with the deviation profile method described in this chapter . For this assessment, the obstacle plane associated with a nominal 3 degree glidepath angle (1:29 slope) should be adjusted according to the maximum approach angle for which approval is sought.
g. Specific conditions.
(1) Failure conditions to be evaluated. The following are failure conditions that should be considered as part of the FGS evaluation program:
(a) Engine failure during approach; continue approach to decision altitude/minimum descent altitude (DA/MDA).
(b) Potential fuel imbalance.
(c) Airplane system failures that affect FGS operational capabilities . Examples include failures of hydraulic systems, electrical systems, flight controls, and FGS-related sensors.
When possible, these failure conditions should be evaluated with a flight test . However, some failure conditions, due to their potential hazards, may best be evaluated via a high fidelity flight simulation.
(2) Failure to disengage. The probability of failure of an FGS element to disengage when the quick disengagement control is operated should be shown to be acceptable by the safety analysis process . If credit is to be taken for acceptable continued manual operation with the FGS elements remaining engaged, that is, without operating any of the other disengagement controls, then a flight demonstration should be conducted through approach, landing, and rollout.
101. Criteria Supporting Operational Use of Autopilot .
a. Typical flight operations. The criteria contained in this paragraph are intended to identify how the functional capability of the FGS, established during the certification, can be used to support typical flight operations . The criteria are based on experience gained from certification programs and functionality provided by traditional systems . A FGS providing 81
10/27/14 A C 25.1329-1C non-traditional functionality—using new or novel technology and/or implementation techniques—may require additional criteria to be established.
b. Operations in close proximity to the ground.
(1) General. During low-visibility operations, multiple redundant autopilot channels may be used, and the effect of any autopilot failures on the flight path may be eliminated or substantially minimized by the protection provided by that redundancy. The considerations in the following paragraphs apply primarily to single channel operations where performance or integrity aspects may require further considera tion. For specific considerations relating to autopilot operations close to the ground in the presence of failures, see Chapter 8, paragraph 88.b, FGS Operations in Close Proximity to the Ground, of this AC.
(2) Considerations. The minimum engagement point for the autopilot after takeoff a nd t he minimum use of the autopilot during approach should take into consideration the effect of the following:
(a) Failures and their effects (that is, failure conditions).
(b) Fault-free performance.
(c) Any specific operational considerations and/or mitigation.
(3) Autopilot engagement altitude/height after takeoff.
(a) Deviation from flight path. The potential deviation of the airplane from the desired flight path due to the effect of a failure condition may necessitate delaying the engagement of an autopilot to an acceptable height above the departure runway.
(b) Worst-case deviation profile. To support the determination of the minimum engagement height, if autopilot failure condition(s) are identified that will cause a significant deviation below the intended vertical flight path, the worst -case deviation profile should be identified. This profile and the recovery of the airplane should not result in penetration of the net flight path as defined in § 25.115.
(c) Other effects. If the failure condition(s) have a neutral effect on the flight pat h but has implications for speed control during takeoff, the acceptability of cues for the flightcrew detection of the condition should be made . The effect of any failure condition relating to the bank angle of the airplane should also be assessed. In all of the above, account should be taken of operating the airplane at the weight/altitude/temperature (WAT) limit.
(d) Minimum engagement height. The minimum engagement height will typically be established, based on the greatest of the following factors:
1 The lowest altitude or height where the flightcrew could reasonably be assumed to engage the autopilot . Consideration should be given to normal flightcrew tasks during rotation and liftoff (typically 100 feet or greater).
10/27/14 A C 25.1329-1C 83 2 Any allowance for the acceptability of the performance of the autopilot during the basic engagement/mode transition.
3 The lowest altitude or height consistent with the response of the airplane to any identified autopilot failure condition(s).
4 Activation of an armed stall identification system, such as a stick pusher (if installed).
(e) Deviation information. If the response to the worst-case failure condition causes a significant transition below the intended vertical flight path, the deviation information should be provided in the AFM.
(4) Autopilot engagement during approach.
(a) Deviation from flight path. The potential deviation of the airplane from the desired flight path due to the effect of a failure condition may necessitate the disengagement of an autopilot at an appropriate height on the approach to landing.
(b) MUH-approach. The operational MUH for approach will be established, base d on t he following considerations:
1 The altitude or height at which the performance of the automatic control is no longer acceptable.
2 The lowest altitude or height consistent with the response of the airplane to a subsequent autopilot failure.
3 Any specific operational consideration.
(c) Approach with vertical path reference.
1 Approaches with vertical path reference can include xLS or RNAV .
Operations using xLS can be assumed to be conducted with respect to a flight path prescribed or established as an integral part of navigation service provided by the State . RNAV approach operations will be conducted using an onboard database that provides a navigation flight path to the runway.
2 The operational consideration for this type of operation relates to an assessment of the adequacy of continued use of the autopilot in maintaining the desired vertical flight path. Considerations include the lowest altitude consistent with the response of the airplane to an autopilot failure.
3 To support this determination, if one or more autopilot failure condition(s) is identified that causes a significant transition below the intended vertical flight path, the worst-case deviation profile should be identified using the method identified in Chapter 9, paragraph 100.f(1), Approach with Vertical Path Reference , of this AC. If the failure condition(s) has a neutral effect on the flight path, the acceptability of cues for the flightcrew
AC 25.1329-1C CHG 2 detection of the condition should be made . The effect of any failure condition relating to the bank angle of the airplane should be assessed.
4 For the purpose of the airworthiness assessment, the vertical flight path of an xLS and RNAV approach can be assumed to be a flight path of 3 degrees that passes through the runway threshold at an altitude of 50 feet. Considerations for steep approaches are provided in Chapter 9, paragraph 99.d(5) of this AC.
5 The vertical flight path control for an xLS approach will be made with reference to the path defined by the navigation service . The RNAV vertical flight path will typically be conducted with reference to barometric altitude. An appropriate adjustment to the MUH may be necessary to take into account the vertical accuracy of RNAV operations.
Note: Temperature effect compensation should be considered as part of the operational authorization.
6 The MUH-Approach is the value identified using the method identified in AC 25-7D, paragraph 33.7.10.5.
(d) Approach without vertical path reference.
1 Flight operations with no vertical path reference are conducted with an appropriate visual segment for the final approach path. In the interest of providing appropriate automatic control to assist in a stabilized approach, the minimum use of the autopilot should be consistent with the performance needed for the descent (for example, vertical speed/flight path angle) and the pilot detection and recovery from an autopilot failure.
2 To support this determination, if one or more autopilot failure conditions are identified that cause a significant transition below the intended vertical flight path, the worst-case deviation profile should be identified. If the failure condition has a neutral effect on the flight path but has implications for speed control during approach , the acceptability of cues for the flightcrew detection of the condition should be made . The effect of any failure condition relating to the bank angle of the airplane should be assessed.
3 For FGS that are failure protected (that is, fail -passive), the MUH will typically be no lower than 50 feet above runway elevation. However, when determining this limitation, account should be taken of the handling task presented to the pilot when regaining manual control, especially in limiting crosswind conditions.
4 For FGS that are not failure protected (that is, not fail-passive), the demonstrated MUH-Approach will typically be established based on the greater of the following considerations:
(aa) 50 feet above runway elevation.
(bb) Two times the height loss for the airplan e as a result of any identified autopilot failure condition, using the method identified in AC 25-7D, paragraph 33.7.10.5.
(5) Circling approach.
(a) For the purpose of this AC, circling approaches may be considered to have the following visual segments associated with the approach:
1 A segment at or above the minimums prescribed by the procedure that parallels the runway in the opposite direction of the landing runway, 2 A turning segment to align with the runway that can be level or partially descending, and 3 A final descending segment to landing.
(b) Operationally, the autopilot may remain engaged even after leaving the MDA(H) for reasons related to safety and flightcrew workload relief . This operational procedure should be balanced against unacceptable performance or failure characteristics . As this procedure is in the visual segment, no specific constraints for the use of the autopilot are considered necessary for this phase of flight, unless specific unacceptable performance or failure characteristics related to circling approach are identif ied during the certification program.
c. Climb, cruise, descent, and holding. The value of the use of the autopilot in providing flightcrew workload relief in climb, cruise, descent, and holding phases of flight should be balanced against the failure characteristics of the autopilot . No specific constraints for the use of the autopilot are considered necessary for these phases of flight, unless specific unacceptable performance or failure characteristics related to climb, cruise, or descent are identified during the certification program.
d. Maneuvering . No specific constraints for the use of the autopilot are considered necessary for maneuvering flight, unless unacceptable performance or failure characteristics are identified during the certification program . Chapter 9, paragraph 100.e, Maneuvering, of this AC provides assessment criteria for maneuvering flight for autopilot failures.
102. Automatic Disengagement of the Autopilot . The automatic disengagement of the FGS will occur for several reasons, such as system failures, sensor failures, or unusual accelerations .
The automatic disengagement characteristics of the FGS should be investigated throughout the flight envelope. These disengagement cases should be analyzed to determine the ones that can be demonstrated during the test program . For each disengagement case, the transients, warnings, and pilot workload for recovery should be evaluated, and compliance with § 25.1329(d) and (e) must be verified. The use of simulation is recommended for all conditions that are expected to result in significant transients.
103. Assessment of Human Factors.
a. General. The evaluation, demonstration, and testing should assess the acceptability of the HMI with the FGS and the potential for flightcrew errors and confusion concerning the behavior and operation of the FGS, when used by a representative range of pilots . The evaluation of normal and non-normal FGS operations should include the representative range of conditions in terms of crew mental or physical workload, required crew response
10/27/14 A C 25.1329-1C timeliness, and potential for confusion or indecision. The set of test cases should represent operationally relevant scenarios and the assumptions about pilot training and skill level should be documented.
b. Flight evaluations.
(1) During certification. Flight evaluation during certification is a final assessmen t a nd is intended to validate the design.
(2) Prior to certification. Evaluations prior to certification are typically conducted in a variety of ways and at different levels of fidelity in order to finalize the design. These may include the following:
(a) Engineering evaluations and task analyses, including cognitive and physical tasks.
(b) Mock-up evaluations and demonstrations.
(c) Part-task evaluations and demonstrations.
(d) Simulator evaluations, demonstrations, and tests.
(e) Engineering flight evaluations, demonstrations, and tests.
(3) Credit to establish FGS compliance. The data and experiences from these evaluations may be useful for credit to establish FGS compliance with regulations having human factors considerations . In addition, applicants have successfully used comparisons to previously certificated designs to obtain such credit (although such credit is not assured) . Additional testing may be necessary for new FGS flightcrew interface designs or functions.
(4) Simulation versus flight tests. In some cases, the FAA may consider that less flight testing may be required to show compliance, if the simulation evaluations have added confidence with respect to the reduced potential for crew error and confusion and other human factors attributes of the pilot/FGS interface.
(a) Selecting methodology. In many cases, the evaluation, demonstration, and test scenarios, including failures and environmental events, will determine whether the data should be obtained in simulation or in flight because of safety considerations or the unavailability of the necessary environmental conditions.
(b) High fidelity simulation. In some test scenarios, a very high fidelity simulation will be needed. In addition to the simulation validation considerations ide ntified in Chapter 9, paragraph 99.e(3)(b), Motion Base Suitability, of this AC, the simulation used may need to include the following features, depending on the functionality of the FGS:
1 Physical implementation of flight deck controls, displays, indicators, and annunciators for all flightcrew positions that are relevant to the objectives of the evaluation.
2 Adequate emulations of relevant equipment (hardware and software function), including capability to introduce failures.
3 Weather simulation, including gusts, turbulence, windshear, and visibility.
4 Representation of the operational environments, including interaction with air traffic services, day/night operations, etc., as relevant to the functions and pilot tasks being evaluated.
5 Data collection capabilities.
(c) Simulation conformity. In some cases, certification credit or demonstration of compliance using simulations may not be granted due to inability to find simulation conformity.
Conformity should be accounted for when seeking certification testing credit using a simulator.
c. Structured subjective evaluations. Simulator evaluations and tests are intended t o g enerate objective and/or subjective data. It may not always be possible or necessary to obtain quantifiable measurements of flightcrew performance, even with high fidelity flight or simulation evaluation, demonstration, or test scenarios . In these cases, evaluation procedures should be based on the use of structured subjective methods, such as rating scales, questionnaires, and/or interviews . When there is dependence on this type of data, evaluations should consider multiple data collection techniques with an appropriate number of pilot evaluators.
d. Pilot training and experience. In order to provide sound evaluations, pilots should be trained appropriately on the FGS operation and procedures . They should have experience in the kinds of operation and aircraft types for which the FGS is intended. Finally, they should be familiar with the intended function of the FGS, its operational and design philosophy, and the way that this philosophy fits with the overall flight deck and its operational and design philosophy.
e. Evaluating new or unique design features. Rationale should be provided for decisions regarding new or unique features in a design. It should be confirmed that the data resulting from the evaluations support acceptability of any new or unique features.
f. Certification planning documentation. The certification planning documentati on s hould describe the means to show compliance with the human factors related considerations of the FGS with this AC.
104—108 [RESERVED] 87
AC 25.1329-1C CHG 2 CHAPT ER 10. AIRPLANE FLIGHT MANUAL
109. General. The following paragraphs provide guidance on material to be provided in the AFM to ensure that the appropriate information related to FGS operation is translated into air carrier operations. For additional guidance, note that AC 25.1581-1 Change 1, addresses requirements of the AFM for transport category air planes and distinguishes between those aircraft that are used in air carrier operations and those not in air carrier service.
a. AFM terminology. The terminology used in the AFM should be consistent with the intended operational use.
b. Low-visibility operations. Appropriate AFM information related to low-visibility operations is addressed in AC 20-191.
110. Information Supporting Operational Use of Autopilot .
a. General. The airworthiness certification process will assess the effect of autopilot Failure Conditions as identified in Chapters 8 and 9 of this AC. If a specific MUH is necessary, then the height should be provided in the AFM limitations section. If the design is such that the effects of one or more failure conditions do not require establishment of a MUH, then the pertinent deviation profile or height loss information should be provided in the normal or non-normal procedures section of the AFM, as applicable.
b. Specif ying a MUH. If a MUH or a height loss value is applicable, it should be specified as follows:
(1) Takeoff—autopilot engagement altitude or height.
(2) Cruise—height loss.
(3) Approach—MUH or height loss.
(a) Approach with vertical path reference. The MUH should be determined based on clearance above a 1:29 plane using the deviation profile method, as discussed in AC 25-7D, paragraph 33.7.10.5, and shown in figure 33-2, Deviation Profile Method, of that AC.
(b) Approach without vertical path r eference. The height loss should be determined using the height loss method, as discussed in AC 25-7D, paragraph 33.7.10.5, and shown in figure 33-3, Height Loss Method, of that AC.
(c) Assessment of approach with vertical path r eference. As shown in AC 25-7D, figure 33-2, Deviation Profile Method.
c. Maximum displacement deviation . If minimum engagement altitude(s) or height(s) are not specified, then “maximum displacement deviation” information from a pertinent takeoff flight path and approach profile should be provided in the AFM normal procedures section, or in the associated flightcrew operation manual (FCOM).
10/27/14 A C 25.1329-1C
111. Limitations. The AFM limitations section presents those FGS operating limitations appropriate to the airplane model as established in the course of the type certification process .
T he FGS operational limitations listed in the AFM (should any exist) must specify a ny c onfiguration/envelope restrictions . See §§ 25.1581(a)(1) and 25.1583.
112. Non-Normal/Emergency Procedures . The AFM must include non-normal or emergenc y pr ocedures appropriate to the FGS identified during the certification program . See § 25.1581(a)(1) and § 25.1585(a)(2) and (a)(3).
113. Normal Procedures.
a. Documentation of normal procedures. The normal procedures for use of the FGS must be documented in the AFM. See §§25.1581(a)(1) and 25.1585(a)(1). These procedures should be demonstrated during the type certification process.
b. Maximum displacement deviation. In lieu of specification of minimum engagement altitude(s) or height(s) (see paragraph 110 of this AC), the AFM may alternately specify “maximum displacement deviations” from a specified takeoff flight path or from a specified approach profile. This information may be based on typical departure or approach flight paths suited for the aircraft type and for failure conditions that are determined applicable to the type of FGS and modes suitable for use.
c. Procedures for use of FGS in icing conditions. The flight manual should include an y ne cessary procedures for the use of the FGS in icing conditions (including moderate and heavy icing conditions). In particular, the procedures should include any necessary changes in operating speeds, required either operationally or as a result of relevant design features of the speed protection function of the FGS. For example, variations in minimum speeds as a function of de/anti-icing system selection, speed increments d uring approach, and landing in turbulence should be part of the documented procedures.
d. Aircraft with published FCOMs. The AFMs for aircraft for which the manufacturer has published a FCOM must contain essential information on normal operating procedures that are considered unique to the operation of the FGS for the aircraft type or are otherwise necessary for safe operation. See § 25.1581(a)(2). FGS description and integration with the overall flight deck design philosophy, specification, and operational procedures that are normally associated with FGSs should be included in the FCOM . If applicable, a FCOM may contain the “maximum displacement deviation” information described in paragraph 110 of this AC in either numeric or graphic form.
e. Aircraft without published FCOMs. For aircraft that rely on the AFM as the sol e ope rating manual, the AFM must contain operating information sufficient for flightcrew reference. See § 25.1581(a)(2). The FGS description and integration with the overall flight deck design philosophy, specification, and operational procedures normally associated with FGSs, should be made available so that an appropriately trained flightcrew may operate the FGS under normal conditions.
10/27/14 A C 25.1329-1C Append ix A APPENDIX A. SAFETY ASSESSMENT
1. General. This appendix provides material that may be useful in supporting the safet y a ssessment activities identified in Chapter 8 of this AC.
2. Identification of Failure Conditions.
a. The following cases should be considered for applicability when establishing failure conditions, as indicated in Chapter 8 of this AC.
(1) Loss of autopilot in single or multiple axes.
(2) Loss of guidance in single or multiple axes.
(3) Loss of thrust control.
(4) Partial loss or degradation of autopilot function.
(5) Unintended autopilot commands in a single axis or multiple axes simultaneousl y ( for example, hardover, slowover, and oscillatory failure modes).
(6) Unintended guidance commands in a single axis or multiple axes.
(7) Unintended thrust control.
(8) A sustained out-of-trim condition with the autopilot engaged without an alert.
(9) Autopilot disengagement in an out -of-trim condition.
(10) Autopilot disengagement without a warning.
(11) Inability to disengage the autopilot or autothrust function.
(12) Uncommanded engagement of an autopilot or autothrust.
(13) Jamming or loading of primary flight controls.
(14) Unintended thrust asymmetry.
b. A typical failure condition statement may be of the form:
‘[Failure]’ during ‘[Phase of Flight]’ that ‘[Effect]’ when ‘[Mitigation Consideration]’
c. Failure conditions may result from failures within the FGS or from failure associate d w ith aircraft interfacing systems or components (for example, NAV receivers, attitude heading reference systems, FMS, hydraulics, electrical systems, etc.).
A-1
10/27/14 A C 25.1329-1C App endix A
3. Considerations when Assessing the Severity of Failure Condition Effects.
a. Complete definition of failure condition. The “failure condition” definition is complete when the effects resulting from the failure are identified . The complete definition of the “failure condition” and its effect will then support the subsequent failure condition hazard classification.
b. Factors to consider. When assessing the effect that results from a failure, the following factors should be considered for various phases of flight:
(1) The impact of the loss of control or unintended control on the structural integrity of the airplane as a result of simple loading or as a result of excitation of aerodynamic or structural modes—both at the time of occurrence a nd while the flight continues.
(2) Implications of the airplane response in terms of attitude, speed, accelerations, flight path, and the impact on the occupants and on flightcrew performance.
(3) Degradation in the stability or other flying qualities of the airplane.
(4) The duration of the condition.
(5) The aircraft configuration.
(6) The aircraft motion cues that will be used by the flightcrew for recognition.
(7) Availability, level, and type of alerting provided to the flightcrew.
(8) Expected flightcrew corrective actio n on detection of the failure.
c. Possible characteristics of failure conditions. Failure conditions may include the following characteristics:
(1) “Hardover” effects. Typically, these are considered significant and are readily detectable by the flightcrew, based on the resulting aircraft motion or guidance cues.
(2) “Slowover” effects. Typically, these are not readily detected by the flightcrew . The effect may involve departures from the intended flight path that are not initially detectable by aircraft motion alone and may be detectable only by motion cues when a significant flight path deviation has occurred or by an appropriate flightcrew alert.
(3) “Oscillatory” effects . Typically, these are repetitive motions or guidance conditions not related to intended guidance or control . The magnitude, period, and duration of the condition and any mitigation considerations will determine the final effect.
(4) “Loss of” effects. Typically, this is the removal of control, guidance , or f unctionality that may have an immediate effect or may not be immediately apparent to the flightcrew.
A-2