32.1.5.3.4 Determine that the malfunction indicators (flags) are appropriately displayed and are satisfactory annunciators.
32.1.5.3.5 Qualitatively assess that the thresholds of displays are wide enough to permit the pilot to follow the indicators, as appropriate to the operation of the airplane.
32.1.5.3.6 Determine that instrument presentation is sufficiently damped to permit use in turbulent air and that hysteresis, if present, is acceptable.
32.1.5.3.7 Verify that the AOA system neither contributes to, nor is affected by, radio frequency or electromagnetic interference (RFI/EMI).
32.1.5.4 Air Data System.
32.1.5.4.1 The air data system performance, except for airspeed calibration, will generally be demonstrated qualitatively by observation of the output displays.
32.1.5.4.2 Be particularly observant of barometric altimeter and vertical speed reversals as a function of rapid pitch attitude changes (e.g., takeoff rotation).
32.1.5.4.3 Verify that the Mach/airspeed indicators operate smoothly throughout the complete speed envelope of the airplane.
32.1.5.4.4 Observe correct operation of the overspeed warning indicator (barber pole) while approaching VMO/MMO speeds.
32.1.5.4.5 Observe the static and total air temperature (SAT/TAT) indicators for reasonableness of data presentation.
32.1.5.4.6 Verify that the air data system neither contributes to, nor is affected by RFI/EMI.
32.1.5.5 Radio Altimeter System.
32.1.5.5.1 The radio altimeter system should display to the flightcrew, clearly and positively, the altitude information that indicates the airplane main landing gear wheel height above terrain.
32.1.5.5.2 Verify that the altimeters display altitude without loss of signal indications or excessive fluctuations, under the following measurement conditions:
Pitch angle ±5° about the mean approach attitude.
Roll angle zero to ±20°.
Forward velocity from minimum approach speed up to 200 knots, in appropriate configurations.
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At altitudes from 0 to 200 feet with sink rates of 0 to 15 feet per second, in landing, approach, and go-around configurations.
32.1.5.5.3 Under the measurement conditions described above, verify that the altimeters track the actual altitude of the airplane over level ground without significant lag or oscillation.
32.1.5.5.4 With the airplane at an altitude of 200 feet or less, verify that any abrupt change in terrain, representing no more than 10 percent of the airplane’s altitude, does not cause the altimeter to unlock. The indicator response to such changes should be appropriate. If the system unlocks, it should re-acquire the signal promptly without pilot intervention.
32.1.5.5.5 Caution should be exercised on airplanes equipped with automatic landing systems if the radio altimeter system is prone to unlock while flying final approach over irregular terrain, since in all probability, the unlock will adversely affect the autoland availability requirement.
32.1.5.5.6 If a decision height (DH) function is provided, verify proper operation at minimum altitudes of 200 feet, 100 feet, and 50 feet.
32.1.5.5.7 Verify that the push-to-test self-test feature generates a simulated radio altitude of less than 500 feet, and that no other systems experience untended effects or interference. For aircraft with automatic landing systems, the self-test feature should be shown to be inhibited during the low altitude phases of the autoland.
32.1.5.5.8 Verify that the system provides a positive failure warning display any time there is a loss of power or a failure of the altimeter to function properly.
32.1.5.5.9 Verify that the radio altimeter system neither contributes to, nor is affected by RFI/EMI.
32.1.5.6 Onboard Weight and Balance System.
AC 20-161 provides guidance for certification of onboard weight and balance systems dated April 11, 2008.
32.1.5.7 Central Aural Warning System (CAWS).
32.1.5.7.1 Most CAWS functions include aural (and voice, in some installations) warnings of the typical airplane conditions specified in table 32-4 below:
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Table 32-4. Types of Aural Warnings
Airplane Condition Aural Warning Engine Fire Altitude Advisory APU Fire Speedbrake Overspeed Autopilot Disconnect Takeoff Flap/Slat Overspeed Stall Cabin Altitude Landing Gear Stabilizer-In-Motion Evacuation Autothrottle Disconnect
32.1.5.7.2 Pilot call and SELCAL tones may also be included, although they are advisories as opposed to warnings.
32.1.5.7.3 The logic for this system usually resides in another computer (e.g., the flight warning computer or master caution/master warning computer) in which case the two systems should be evaluated simultaneously. However, if the logic and/or computer governing activation of the warnings, priority logic, inhibits, etc., are contained in the CAWS itself, refer to the section covering the computers noted above for additional guidance on flight evaluation. Compliance may be shown by equivalent tests in a flight simulator or by bench tests.
32.1.5.7.4 Individual activation of each warning tone should be accomplished in flight under the most adverse noise conditions appropriate to the warning
(e.g., VMO/MMO for overspeed, high speed descent for APU fire, acceleration following takeoff for flap/slat overspeed, etc.). Test switches and/or the self-test feature of the system would be an appropriate means to activate the warning.
32.1.5.7.5 The flight evaluation will be a pilot qualitative assessment of the clarity, tone, and volume of each warning.
32.1.5.8 Overspeed Warning System.
This system should be demonstrated in conjunction with the airspeed system calibration and should exhibit that it is consistently within the prescribed tolerances. The system tolerance is from VMO to VMO + 6 knots in the airspeed limited range, and from MMO to MMO + 0.01 M in the Mach limited range.
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32.1.5.9 Altitude Advisory (or Altitude Alerting) System.
32.1.5.9.1 A ground test should be conducted to check the adequacy of the required pre-flight procedure provided in the AFM.
32.1.5.9.2 A flight demonstration should be conducted at low, mid, and high altitudes to verify performance of the intended function of:
Alerting to, and Alerting to an uncommanded departure from an assigned (selected) altitude.
32.1.5.9.3 Low and high rates of vertical speed should be included in the evaluation with captures from above and below the pre-selected altitude.
32.1.5.9.4 Determine adequacy of the alert light location and its visibility under various lighting conditions, and adequacy of the aural warning.
32.1.5.9.5 A flight simulator may be used to perform appropriate tests.
32.1.5.10 Terrain Awareness and Warning System.
AC 25-23 contains guidance for flight test considerations for TAWS approvals.
32.1.5.11 Master Caution System (MCS)/Master Warning System (MWS).
32.1.5.11.1 This system provides inputs to master warning and master caution lights located on the glareshield in front of each pilot and to the CAWS. (See paragraph 32.1.5.8 of this AC.) It contains the sensors, switches and logic required to assess the requirement for the warning and caution annunciations.
32.1.5.11.2 The system may contain logic to assess priority of the various warnings in order to sequence simultaneous actuation. If so, ground, flight, or bench tests may have to be conducted to verify this logic.
32.1.5.11.3 Some cautions may be inhibited during various phases of flight, particularly during the final stages of a Category III automatic landing operation (below alert height). If so, ground or flight tests may have to be structured to verify the inhibit logic. Also, certain warnings may be inhibited during the high-speed stages of a takeoff roll. If this feature is incorporated, it too should be carefully substantiated.
32.1.5.11.4 Simulate failure of selected sensor inputs to verify that the MCS/MWS computer detects the faults and illuminates the fail annunciator (if installed).
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32.1.5.11.5 Verify that there is no unacceptable mutual interference between the MCS/MWS and other systems and equipment.
32.1.5.12 Flight Warning Computer (FWC).
32.1.5.12.1 The FWC is a key subset of the overall warning, caution, and alerting system on the more modern airplanes. It is a microprocessor-based system that works in conjunction with, or totally replaces, the CAWS and MCS/MWS.
32.1.5.12.2 The FWC incorporates sufficient computer capacity to perform many more functions than the MCS/MWS and, in addition to outputting to the visual warning displays and aural warning speakers, outputs hundreds of alerts/messages to other display media, most often an electronic display (multi-function CRT on the instrument panel or the CDU portion of the FMS).
32.1.5.12.3 The added computer capacity also enables incorporating rather complex inhibit algorithms which, in turn, dictates a requirement for structuring a very complex ground test to verify operation of the inhibits. Review of the system description document will probably be required before any ground, flight, or bench tests can be defined.
32.1.5.12.4 The flight evaluation should incorporate the tests described under CAWS and MCS/MWS.
32.1.5.12.5 Verify that the self-test feature functions properly.
32.1.5.12.6 Simulate failure of selected sensor inputs to verify that the FWC detects the faults and illuminates the FWC fail annunciator.
32.1.5.12.7 Demonstrate freedom from nuisance warnings by observing and logging nuisance events as they occur throughout the flight demonstration program. Assess the status at the end of the program by examining the log.
32.1.5.13 Stall Warning Computer (SWC).
32.1.5.13.1 The SWC should be evaluated in conjunction with the stall tests described in chapter 8 of this AC. Adequacy of the various warnings (stick shaker, warning light, aural (and voice) warning) should be assessed, in addition to the speed schedules.
32.1.5.13.2 Demonstrate freedom from nuisance warnings during the takeoff, landing, and maneuvering flight tests described in chapter 8 of this AC. Further testing may be required to show freedom from nuisance warnings by the test requirements in chapter 42 of this AC, if special airworthiness approvals are sought.
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32.1.5.14 Takeoff Warning (TOW) System.
32.1.5.14.1 The TOW system is usually a subset of the CAWS or MCS/MWS or FWC and is generally inhibited at nose wheel liftoff during the takeoff maneuver. It is usually armed when the squat switch indicates that the airplane is on the ground and one or more power or thrust levers are advanced beyond a prescribed position or engine power or thrust setting.
The system alarms if the flaps/slats/stabilizer/spoiler/brakes are not set correctly for takeoff.
32.1.5.14.2 Determine that each event is annunciated properly by conducting a static ground test.
32.1.5.14.3 Flight evaluation during takeoff roll should be a qualitative assessment of the clarity, tone, and volume of each warning. Some systems incorporate a TEST switch, which facilitates activation during takeoff. If this feature is not available, it may suffice to check the audio level of a warning during touch and go landings (e.g., the stabilizer warning while accelerating to VR speed).
32.1.5.14.4 Simulate failure of selected sensor inputs to verify that the TOW system detects the faults and illuminates the fail annunciator (if installed).
32.1.5.14.5 Verify that the system’s arming status is not affected by electrical power transients, which occur when switching from ground or APU power, during engine start, following bus priority checks, etc.
32.1.5.14.6 Verify that there is no unacceptable mutual interference between the TOW system and other airplane systems and equipment.
32.1.5.15 Instrument Comparator System.
32.1.5.15.1 If an instrument comparator system is installed and activated, ensure the system monitors validity of and compares (side 1 vs. side 2) pitch and roll attitude, heading, altitude, airspeed, radio altitude, localizer, and glideslope deviation information used for display in the cockpit instruments.
32.1.5.15.2 When these parameters exceed a preset threshold or trip level, or if an invalid condition is detected in any of the displayed information, an appropriate annunciator to that parameter will be illuminated.
32.1.5.15.3 A ground test on the airplane should be conducted to demonstrate performance of intended functions and validate the detector threshold levels. If annunciation is suppressed under certain conditions, these conditions should also be checked.
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32.1.5.15.4 A flight evaluation should also be conducted to determine adequacy of the annunciator light locations and visibility under various lighting conditions and that the annunciators are properly identified.
32.1.5.15.5 During flight, verify that the system is free from nuisance warnings and is compatible with other electronic systems.
32.1.5.16 Reactive Windshear Warning System.
A complete and comprehensive demonstration program (simulator and flight test) is contained in AC 25-12.
32.1.5.17 Traffic Alert and Collision Avoidance System.
A complete and comprehensive demonstration program (laboratory/ground/flight test) is contained in AC 20-131A.
32.1.6 Procedures—Recording Systems.
32.1.6.1 Cockpit Voice Recorder (CVR).
32.1.6.1.1 Demonstrate operation of the CVR self-test function and bulk erase feature.
32.1.6.1.2 During ground operations prior to and after engine start; during takeoff, climbout, and cruise at VMO/MMO; and during landing approach. Except where specifically noted, obtain the following CVR recordings:
1. Flightcrew conversations using the area microphone.
2. Flightcrew conversations using the oxygen mask microphones and the boom-microphone/handset, and the hand-held microphones in flight and during ground operations.
3. Radio transmissions by each crew member during cruise.
4. Audio signals identifying navigation aids (through cockpit speakers and on radio channels) during landing approach.
5. PA announcement during cruise.
6. Selective (based on analysis) aural warning signals (see CAWS) during appropriate flight phases.
32.1.6.1.3 Use CVR circuit breaker to limit CVR recording to available capacity.
32.1.6.1.4 Verify that all controls, displays, and annunciators consistent with normal and abnormal crew procedures, are satisfactorily identified, accessible, operable, and visible.
32.1.6.1.5 EMC. Verify by observation that no adverse effects are present in the required flight systems.
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32.1.6.1.6 Following the flight, test the CVR audio recording in an appropriate laboratory, and evaluate for clarity of the recorded messages. Preferably the evaluators should not have advance information concerning the flightcrew conversations.
32.1.6.1.7 Verify that the hot mike feature at each position allows for recording regardless of the position of the interphone transmit key switch (§ 25.1457(c)(5)).
32.1.6.2 Digital Flight Data Recorder (DFDR).
32.1.6.2.1 Demonstrate operation of the DFDR self-test feature and, prior to collection of test data, set the trip number and date on the code switches of the Trip and Data Encoder, if so equipped.
32.1.6.2.2 The certification data will be derived automatically during any appropriate flight that encompasses operation throughout the full flight envelope.
Hand recorded data of heading (magnetic or true), barometric altitude, pitch attitude, indicated airspeed, and time (UTC) should be collected at several stabilized flight conditions for subsequent data correlation purposes.
32.1.6.2.3 Following the flight, the data should be retrieved for correlation and accuracy verification.
32.1.6.2.4 Demonstrate performance of intended function of the DFDR for all parameters specified in the operating rules. (See appendix B to part 121 for the relevant data ranges, accuracies, and recording intervals.) Accuracy will be verified at stabilized points by correlating against, and comparing with, an approved instrumentation system or manual notes.
32.1.6.2.5 EMC. Verify by observation that no adverse effects are present in the required flight systems.
32.1.7 Engine Interfacing Systems.
[Reserved]
32.1.8 Stability Augmentation Systems.
[Reserved]
32.1.9 All Weather Operation (Reduced Visibility) Systems.
[Reserved] 32-38
32.2 Flight and Navigation Instruments—§ 25.1303.
32.2.1 Explanation.
32.2.1.1 Section 25.1303(b)(1) requires an airspeed indicator to be visible at each pilot station. Additionally, if airspeed limitations vary with altitude, airspeed indicators must have a maximum allowable airspeed indicator showing the variation of VMO with altitude. Presenting this variation in VMO as a marker on the airspeed indicator whose position varies as a function of altitude is an acceptable means of compliance with this requirement.
32.2.1.2 Production tolerances for speed warning devices at VMO/MMO are required to be taken into account in accordance with § 25.1303(c).
32.2.1.3 Section 21.127(b)(2) requires each production flight test to include “An operational check of each part or system operated by the crew while in flight to establish that during flight, instrument readings are within normal range.” Nowhere in these requirements is there any inference that the finite performance or quantitative limits, defined during type certification, need to be determined for each production airplane.
32.2.1.4 Section 25.1303(c) requires that turbine-powered airplanes be equipped with a speed warning device that will provide aural warning whenever the speed exceeds VMO plus 6 knots or MMO + 0.01 M. The regulations specify that the upper limit of the production tolerances permitted for the warning device must be at a speed not greater than the prescribed warning speed.
32.2.1.5 Accuracy requirements specified in §§ 25.1323 and 25.1325 that apply to the airspeed indicator and altimeter required by § 25.1303(b)(1) and (2), respectively, apply equally to all installed airspeed indicators and altimeters, including standby airspeed indicators and altimeters.
32.2.2 Procedures.
The applicant should substantiate, by appropriate ground and/or flight tests, with possible production instrument error corrections, that the system operates within the boundaries established by the regulation. Understanding that other procedures may be acceptable, this could be accomplished in accordance with the following:
32.2.2.1 If the maximum allowable airspeed varies as a function of altitude and is indicated by means other than a maximum airspeed versus altitude presentation in the airspeed indicator, it should be substantiated that the chosen means of maximum allowable airspeed indication provides an accurate presentation of the relationship between VMO and altitude. The indicated VMO should not exceed the actual VMO for any altitude by more than six knots. This is particularly important for airplanes that have a step 32-39
AC 25-7D CHG 1
function in VMO at a specific altitude (e.g., 10,000 feet) due to bird strike considerations below that altitude.
32.2.2.2 During production flights, the speed warning device must provide warning at a speed equal to or less than VMO + 6 knots or MMO + 0.01 M, minus the sum of the values stipulated in 32.2.2.2.1 and 32.2.2.2.2 below:
32.2.2.2.1 The possible error of the airspeed indicator or Mach meter used as the reference.
32.2.2.2.2 Three knots or 0.005 M, if the airspeed indicator or Mach meter used as the reference has a static or pitot pressure source different from the pressure sources of the warning devices.
32.2.2.3 The speed warning device must be shown to comply with the requirements of § 25.1303(c), as explained in paragraph 32.2.2.3.1 and 32.2.2.3.2 below:
32.2.2.3.1 During ground test using calibrated reference instruments, the installed speed warning device must provide warning at a speed equal to or less than VMO + 6 knots or MMO + 0.01 M. The procedure for this test should be processed in accordance with § 21.127(b)(5) or § 21.143(a)(3).
32.2.2.3.2 For each type design, a test should be conducted to show satisfactory correlation between the operation of the warning device during flight and the data obtained during the ground tests.
32.3 Powerplant Instruments—§ 25.1305. [Reserved]
32.4 Miscellaneous Equipment—§ 25.1307. [Reserved]
32.5 Equipment, Systems, and Installations—§ 25.1309.
32.5.1 Explanation.
The following procedures outline and paraphrase the appropriate provisions of § 25.1309. Further definition and explanation, if required, may be found in part 25 and in AC 25.1309-1B.
32.5.2 Procedures.
32.5.2.1 Evaluate functioning of required installed equipment to verify that performance is as intended under any foreseeable operating and environmental conditions.
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32.5.2.2 Evaluate failure conditions, as appropriate, to determine their impact on the capability of the airplane or the ability of the crew to operate it.
32.5.2.3 Review, as appropriate, any design analyses, proposals, studies, or tests that correlate probabilities of failure condition occurrence with the effects of those failure conditions, to determine that they are properly categorized for the appropriate criticality level.
32.5.2.4 Verify that adequate warnings are provided of unsafe conditions, and that these warnings enable the flightcrew to take appropriate corrective action with a minimum of error.
32.5.2.5 In accordance with § 25.1310, for probable operating combinations of required electrical installations, verify that the following power loads are provided for probable durations:
32.5.2.5.1 Loads connected to the system with the system functioning normally;
32.5.2.5.2 Essential loads after failure of any one prime mover, power, converter, or energy storage device;
32.5.2.5.3 Essential loads after failure of one engine on a two-engine airplane;
32.5.2.5.4 Essential loads after failure of two engines on airplanes with three or more engines; and
32.5.2.5.5 Essential loads for which an alternate source of power is required, after any failure or malfunction in any one power supply system, distribution system, or other utilization system.
32.5.2.6 For probable operating combinations of required electrical installations that must be provided with an alternate source of power in accordance with § 25.1331(a), verify that power is provided for probable durations after failure of any one power system.
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CHAPTER 33. EQUIPMENT: INSTRUMENTS INSTALLATION
33.1 Arrangement and Visibility—§ 25.1321. [Reserved]
33.2 Warning, Caution, and Advisory Lights—§ 25.1322. [Reserved]
33.3 Airspeed Indicating System—§ 25.1323.
33.3.1 Explanation.
33.3.1.1 Methods.
33.3.1.1.1 Unless a calibrated reference system is provided, the airspeed system should be calibrated throughout as wide a range as necessary to cover the intended flight tests. The procedures of this section are for the purpose of showing compliance with § 25.1323(b) and are not intended to cover the speed range of the flight tests. If an alternate airspeed indicating system is provided, it should be calibrated. The airspeed indicating system should be calibrated in accordance with the following methods:
33.3.1.1.2 The tests should be conducted in stabilized flight at airspeeds throughout the speed range for the airplane configurations to be tested. The airplane’s airspeed system should be calibrated against a reference airspeed system.
33.3.1.1.3 A reference airspeed system should consist of either of the following:
1. An airspeed impact pressure and static pressure measurement device (or devices) that are free from error due to airplane angular changes relative to the direction of the free stream or due to slipstream variation resulting from changes in airplane configuration or power/thrust. In addition, the device or devices should have a known calibration error when located in the free stream.
2. Any other acceptable airspeed calibration method (e.g., the altimeter method of airspeed calibration).
33.3.1.1.4 If an alternate system is provided, it may be calibrated against either the reference system or the airplane’s system.
33.3.1.1.5 An acceptable means of compliance when demonstrating a perceptible speed change between 1.23 VSR to stall warning speed (§ 23.1223(d)) is for the rate of change of IAS with CAS to be not less than 0.75.
33.3.1.1.6 An acceptable means of compliance when demonstrating a perceptible speed change between VMO to VMO + 2/3 (VDF - VMO) (§ 23.1323(e)) is for the rate of change of IAS with CAS to be not less than 0.50.
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