37-1 CHAPTER 37. MISCELLANEOUS EQUIPMENT
37.1 Electronic Equipment—§ 25.1431.
37.1.1 Explanation.
Section 25.1431(d) requires verification that any electronic equipment will not cause essential loads to become inoperative as a result of electrical power supply transients or transients from other causes. Although this requirement explicitly addresses electrical power supply transients, this requirement is also implicit in other part 25 requirements, specifically:
37.1.1.1 Section 25.1310(a) (Power source capacity and distribution), which states that each installation whose functioning is required and that requires a power supply is considered an “essential load” on the power supply. It requires that the power sources and the system be able to continue to supply power loads under probable critical operating combinations and for probable durations;
37.1.1.2 Section 25.1351(b) (Electrical systems and equipment—General), which requires that electrical generating systems be designed so that no failure or malfunction of any power source can create a hazard or impair the ability of remaining sources to supply essential loads; and
37.1.1.3 Section 25.1353(a) (Electrical equipment and installations), which requires that electrical equipment and controls be installed so that operation of any one unit or system of units will not adversely affect the simultaneous operation of any other electrical unit or system essential to safe operation.
37.1.2 Procedures.
37.1.2.1 Evaluate the possibility of interaction between different systems of communications and navigation equipment. Momentary deflection or flicker can be permitted if it does not result in any deviation to the aircraft flight path when flying a coupled navigation mode. (Flicker frequencies above 55 Hertz for stroke symbology or non-interlaced raster and 30/60 Hertz for interlaced raster are generally satisfactory.) Loss of required function of the usable and assigned frequencies in the national airspace system should be considered unacceptable.
37.1.2.2 Equipment sensitivity to a variety of transient signal conditions is accomplished during laboratory environmental testing (usually accomplished per the methods contained in RTCA Document No.
RTCA/DO-160). However, equipment sensitivity to normal airplane systems electrical transients should be evaluated during flight testing. This
37-2 can be accomplished by observing the operation of flight essential equipment while:
37.1.2.2.1 Reconfiguring the electrical generating and distributing system (e.g., opening/closing bus-tie breakers, supplying the various electrical busses with other source of power, e.g., right main bus from left integrated drive generator, etc.).
37.1.2.2.2 Switching on/off high current demand systems such as galley ovens, hydraulic pumps, cabin lighting, in-flight entertainment systems, power supply systems for portable electronic devices, seat actuators, and
37.1.2.2.3 Any other high-current airplane system that would normally be operated during flight.
37.2 Equipment Standards for Oxygen Dispensing Units—§ 25.1447.
37.2.1 Explanation.
37.2.1.1 Section 25.1447(c)(2)(i) requires that each flightcrew member be provided with an oxygen dispensing unit that can be taken from its ready position and placed on the face using one hand, properly secured, sealed, and supplying oxygen upon demand within five seconds without disturbing eyeglasses or causing delay in accomplishing emergency duties.
37.2.1.2 Showing compliance with this rule involves measuring human performance, which is inherently variable. In order to take variations in human performance into account, multiple tests of donning each oxygen mask should be conducted. In determining whether compliance has been shown, it is important to consider both the average mask donning time and the variation in donning times as noted below:
37.2.1.2.1 The average time to don the mask should indicate that the 5-second requirement is met.
37.2.1.2.2 Even if the average donning time is five seconds or less, it may take longer than 5 seconds to don the mask for 50 percent or more of the tests.
Therefore, it is also important to establish a criterion regarding the distribution of test results in order to ensure that the mask can be consistently donned within five seconds.
37.2.2 Procedures.
37.2.2.1 A donning test should be conducted from each required flight crewmember station whenever the oxygen mask, storage location, or means of stowing the mask is established or changed. Each donning test should consist of at least five donning events. The donning tests may be
37-3 conducted in an airplane, a simulator, or a flight deck mockup that accurately reflects the proposed design.
37.2.2.2 The test should be witnessed by an FAA or designated engineering representative (DER) test pilot. It is acceptable, but not required, to use appropriately qualified flight crewmembers as test subjects.
37.2.2.3 Prior to starting each mask-donning event at each pilot station, the pilot should be seated at the design eye reference position with the seat belt and shoulder harness fastened. One hand should be on the control wheel and the other on the throttles. For other flight crewmember duty positions
(e.g., flight engineer), appropriate seating and hand positions may be determined on a case-by-case basis. Either hand may be used to don the mask.
37.2.2.4 Since § 25.1447(c)(2)(i) requires the five second donning criterion to be met without disturbing eyeglasses, the test subjects must wear glasses during the test. Daytime lighting conditions may be used, unless flight deck arrangement and lighting systems suggest that locating and retrieving the mask may be difficult in nighttime lighting conditions.
37.2.2.5 Timing should begin when the start of the test event is announced by the test director, and end when the mask is properly sealed on the pilot’s face with eyeglasses in place. The method of initiating the test event and determining when the mask is sealed is at the discretion of the test participants. A stopwatch, or other means shown to be reasonably accurate, may be used to time the tests.
37.2.2.6 For each donning test:
37.2.2.6.1 At least 80 percent of the donning events should be completed in 5 seconds or less.
37.2.2.6.2 The average time for each donning test should be five seconds or less.
38-1 CHAPTER 38. OPERATING LIMITATIONS AND INFORMATION: GENERAL [RESERVED]
39-1 CHAPTER 39. OPERATING LIMITATIONS AND INFORMATION:
OPERATING LIMITATIONS [RESERVED]
40-1 CHAPTER 40. OPERATING LIMITATIONS AND INFORMATION:
MARKINGS AND PLACARDS [RESERVED]
41-1 CHAPTER 41. OPERATING LIMITATIONS AND INFORMATION:
AIRPLANE FLIGHT MANUAL
41.1 General—§ 25.1581.
41.1.1 Explanation.
The primary purpose of the AFM is to provide an authoritative source of information considered to be necessary for safe operation of the airplane. Since the flightcrew is most directly concerned with operation of the airplane, the language and presentation of the flight manual should be directed principally to the needs and convenience of the flightcrew, but should not ignore the needs of other contributors to safe operation of the airplane in accordance with the applicable operating regulations.
41.1.1.1 Section 25.1501 requires that the operating limitations specified in §§ 25.1503 through 25.1533, and other information necessary for safe operation, be included in the AFM, be expressed in markings and placards, and also be made available by any other means that will convey the necessary information to the crew members.
41.1.1.2 Information and data that are mandatory for an acceptable AFM are prescribed in §§ 25.1581 through 25.1587. The material required by 14 CFR parts 25 and 36 must be included in the AFM. At the option of the applicant, the AFM may be expanded to contain additional FAA approved information.
41.1.1.3 The manufacturer or operator may include other “unapproved” data in a separate and distinctively identified portion of the AFM.
41.1.2 Reference.
See AC 25.1581-1, Change 1, for detailed guidance on the required content and general structure of the AFM.
41.2 [Reserved.]
42-1 CHAPTER 42. AIRWORTHINESS: MISCELLANEOUS ITEMS
42.1 Design and Function of Artificial Stall Warning and Identification Systems.
42.1.1 Applicable Regulations.
Sections 25.103, 25.201, 25.203, and 25.207.
42.1.2 Explanation.
Some airplanes require artificial stall warning systems to compensate for a lack of clearly identifiable natural aerodynamic stall warning to show compliance with the stall warning requirements of § 25.207. A stick shaker is a recommended method of providing such a warning, regardless of whether or not the natural aerodynamic stall warning is clearly identifiable. Similarly, some airplanes require a stall identification device or system (e.g., stick pusher,) to compensate for an inability to meet the stalling definitions of § 25.201 or the stall characteristics requirements of § 25.203. In addition to compliance with the flight test requirements prescribed in paragraph 8.1 of this AC, certain system design and function criteria should also be addressed during the certification process of these airplanes. Included are system arming and disarming, preflight checks, failure indications and warnings, and system reliability and safety. The reliability of these systems can be evaluated in terms of the probability of the system not operating when required, and the safety aspects in terms of the probability of the system operating inadvertently. The required reliability and safety of stall warning and identification systems should be defined as a function of how critical their respective functioning is to safety of flight.
42.1.3 Arming and Disarming.
42.1.3.1 Stall warning systems should be armed any time the airplane is in flight
(i.e. from main gear liftoff to touchdown). However, up to the end of the takeoff rotation (i.e., until the takeoff pitch attitude is attained), any phase advance feature of the stall warning system (i.e., the portion of the algorithm for activating the stall warning system that responds to the rate of change in angle-of-attack) can be inhibited.
42.1.3.1.1 Arming of stall warning systems has typically been accomplished by a ground/air logic circuit, which requires the nose and/or main gear squat switches to sense air mode before the system is armed. A pitch angle threshold during rotation has also been used to arm the stall warning system. These types of system arming schemes provide stall warning protection during liftoff and initial climb, where a stall would most probably have catastrophic consequences. They also provide protection against nuisance warnings during the takeoff roll, where the angle-ofattack (AOA) sensor vanes may be misaligned. Service history, however, has shown that systems armed around the liftoff point have caused pilots to abort takeoffs due to false alerts resulting from stall warning system faults or failures. In some cases, these high-energy rejected takeoffs have
42-2 resulted in overruns. Therefore, system faults and failures that would lead to a false stall warning near liftoff should be made evident as early in the takeoff as practicable.
42.1.3.1.2 In accordance with the requirements of § 25.207(b), if a stall warning system is required for any normal combination of flap and landing gear position, it must be used for all combinations of flap and landing gear positions. The purpose of this requirement is to provide a standard, consistent warning to the flightcrew of an operational flight envelope limit.
42.1.3.2 Stall identification systems should be armed any time the airplane is in flight.
42.1.3.2.1 The arming should take place automatically and may be provided by the same ground/air sensing system used for arming the stall warning system.
The stall identification system may be inhibited during the takeoff rotation, but should become functional immediately after main gear liftoff.
For airplanes with both stall warning and stall identification systems, it is permissible to have the stall identification system armed by operation of the stall warning system, provided the resulting probability of the stall identification not to operate when required is not greater than that specified in paragraph 42.1.5 below.
42.1.3.2.2 Stall identification systems may incorporate automatic disarming in flight regimes where the risk of stalling is extremely remote or where their unwanted operation would pose a threat to continued safe flight; examples of such inhibits would be high airspeed, and “g” cutouts (typically 0.5 g), and while the pilot is following windshear recovery flight director guidance.
42.1.3.2.3 A means to quickly deactivate the stall identification system should be provided and be available to both pilots. It should be effective at all times, and should be capable of preventing the system from making any input to the longitudinal control system. It should also be capable of canceling any input that has already been applied, from either normal operation or from a failure condition.
42.1.3.2.4 If a stall identification system is required to show compliance with the stall requirements of part 25 in one (or some) airplane configuration(s), it does not have to be used for stall identification in configurations where compliance can be demonstrated without it. Unlike stall warning, the stall point, be it aerodynamic or artificially induced, represents an end-point outside the in-service operational envelope of the airplane, and, therefore, does not need to be provided by the same means for all flap and landing gear configurations. Additionally, the added system complexity, and
42-3 increased exposure to malfunctions and failures, would not warrant the use of a stall identification system for configurations where it is not required.
42.1.4 Indicating and Warning Devices.
42.1.4.1 A method should be provided to allow the pilot to determine that the stall warning and stall identification systems are operating properly prior to takeoff. This method should be described in the operating procedures section of the AFM.
42.1.4.2 Warning that the associated systems for operating the stall warning or stall identification devices has failed should be provided. As far as is practicable, this warning should cover all system failure modes.
42.1.4.3 A clear and distinctive cockpit indication should be given when the stall identification system has been deactivated by the flightcrew (see paragraph 42.1.3.2.3 above). This indication should be present as long as the system is deactivated.
42.1.4.4 Any related limitations, and normal and emergency operating procedures, together with any information found necessary for safety during operation of the stall warning and identification systems, should be included in the AFM and supplemented by such markings and placards as deemed necessary.
42.1.5 System Reliability and Safety.
When stall warning and/or stall identification systems are installed to show compliance with the stalling requirements of §§ 25.201, 25.203, and 25.207, engineering data should be supplied to satisfy the following criteria, determined in accordance with § 25.1309.
42.1.5.1 Reliability.
Probability of artificial stall warning and stall identification systems not operating when required:
42.1.5.1.1 If stall warning is not clearly identifiable by natural characteristics, the loss of artificial stall warning should be improbable (not greater than 10-5 per flight hour). This reliability requirement is normally met by using dual, independent stall warning systems.
42.1.5.1.2 If the natural stall characteristics are unacceptable, the combination of failure of the stall identification system to operate and entry into a stall should be extremely improbable (not greater than 10-9 per flight hour). A stall identification system with a failure rate not greater than 10-4 per flight hour will satisfy this requirement.
42-4
42.1.5.1.3 If the stall identification system is installed solely for the purposes of identifying the stall, and the stall characteristics would otherwise meet the requirements of Subpart B with the stall identification system disabled, a maximum failure rate of 10-3 per flight hour will be acceptable.
42.1.5.2 Safety.
Probability of artificial stall warning and stall identification systems operating inadvertently:
42.1.5.2.1 The probability of inadvertent operation of artificial stall warning systems, during critical phases of flight, should not be greater than 10-5 per flight hour.
42.1.5.2.2 To ensure that inadvertent operation of the stall identification system does not jeopardize safe flight, and to maintain crew confidence in the system, it should be shown that:
No single failure will result in inadvertent operation of the stall identification system; and The probability of inadvertent operation from all causes is improbable (not greater than 10-5 per flight hour).
42.1.5.2.3 Stall identification systems should be designed so that flight in turbulence will not result in inadvertent operation.
Note: In making the assessments of paragraphs 42.1.5.2.4, 42.1.5.2.5, and
42.1.5.2.6 below, it should be assumed that in the climb, cruise, and descent flight regimes, corrective pilot action will not be initiated until three seconds after unwanted operation has been recognized. During takeoff and final approach, this time delay may be reduced to one second.
42.1.5.2.4 If inadvertent operation of the stall identification system would result in limit loads being exceeded in any part of the airplane structure, the probability of inadvertent operation should not be greater than 10-7 per flight hour.
42.1.5.2.5 If inadvertent operation of the stall identification system would result in ultimate loads being exceeded in any part of the airplane structure, the probability of inadvertent operation should be extremely improbable (not greater than 10-9 per flight hour).
42.1.5.2.6 Inadvertent operation of the stall identification system should not cause catastrophic ground contact. This should be achieved by limiting the effect of the stall identification system to that necessary for stall identification purposes, without undue flight path deviation (e.g., by limiting the stroke of a stick pusher). Alternatively, if inadvertent operation could result in catastrophic ground contact according to § 25.1309(b)(1), the probability of inadvertent operation must be extremely improbable. Inhibition of the
42-5 system close to the ground (e.g., for a fixed time after liftoff or below a radar altitude) would not normally be an acceptable means of compliance with this requirement.
42.1.6 System Functional Requirements.
42.1.6.1 Operation of the stall identification system should reduce the airplane’s angle-of-attack far enough below the point for its activation that inadvertent return to the stall angle-of-attack is unlikely.
42.1.6.2 The characteristics of stall identification systems, which by design are intended to apply an abrupt nose-down control input (e.g., a stick pusher), should make it unlikely that a flightcrew member will prevent or delay its operation. The required stick force, rate of application, and stick travel will depend on the airplane’s stall and stick force characteristics, but a force of 50 to 80 lbs applied virtually instantaneously has previously been accepted as providing this characteristic.
42.1.6.3 Normal operation of the stall identification system should not result in the total normal acceleration of the airplane becoming negative.
42.1.6.4 The longitudinal maneuvering capability of an airplane equipped with stall identification systems, at all speeds likely to be encountered in normal operations, should be substantially the same as would be expected for an airplane with acceptable aerodynamic stall characteristics.
42.1.7 System Tolerances.
See paragraph 8.1.9 for additional considerations regarding compliance with stall-related regulatory requirements, including how to address tolerances for stall speed (§ 25.103) and stall characteristics (§ 25.203) testing. See paragraph 8.1.6.2.6 for how to address tolerances of the stall warning and stall identification systems during testing to show compliance with the stall warning requirements (§ 25.207).
42.2 Reduced and Derated Power or Thrust Takeoff Operations.
42.2.1 Explanation.
The use of derated and reduced power or thrust for takeoff operations can produce substantial reductions in operating costs due to lower fuel consumption and increased operating margins. With the appropriate limitations and operating procedures applied, these operations can also offer safety benefits. Three methods have been approved by the FAA for derated and reduced power or thrust takeoff operations. These methods are as follows:
42.2.1.1 Derated power or thrust approvals entail the use of completely new takeoff power or thrust setting charts and AFM performance information. The new power or thrust settings are less than the engine manufacturer’s