CHAPTER 38. OPERATING LIMITATIONS AND INFORMATION: GENERAL [RESERVED] 38-1
CHAPTER 39. OPERATING LIMITATIONS AND INFORMATION:
OPERATING LIMITATIONS [RESERVED] 39-1
CHAPTER 40. OPERATING LIMITATIONS AND INFORMATION:
MARKINGS AND PLACARDS [RESERVED] 40-1
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.] 41-1
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 42-1
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 42-2
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.
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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 42-4
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 42-5
approved takeoff power or thrust settings, and the AFM performance is based on the power or thrust developed at these new, lower power or thrust settings.
42.2.1.2 A constant reduced power or thrust increment can be used for all operating conditions. In this method the engine parameter by which power or thrust is set is reduced by a constant, such as an engine pressure ratio increment (ΔEPR) of 0.02. A method is supplied to determine the airplane’s takeoff performance, at this reduced power or thrust level, from the AFM data representative of full takeoff power or thrust.
42.2.1.3 The assumed temperature method of reduced power or thrust takeoff operations entails using takeoff performance information determined for an “assumed” temperature above ambient, but not above the temperature at which the takeoff weight would be limited by the takeoff field length available for a particular airport runway or by FAA climb requirements.
Engine power or thrust settings, takeoff speed schedules, takeoff field lengths, and climb performance are determined at the assumed temperature. This assumed temperature method is the most flexible in its application and the most widely used by transport category airplane manufacturers and operators.
42.2.2 Procedures.
Because there is a reduction in the takeoff performance level when any of the derated or reduced power or thrust methods are used, the FAA has certain limitations on the use of these reduced power or thrust levels. The appropriate guidance for derated and reduced power or thrust approvals, including limitations and procedures, is presented in AC 25-13.
42.3 Runway Gradients Greater than ±2 Percent.
42.3.1 Applicable Regulations.
Sections 25.105, 25.115, 25.119, 25.121, 25.125, 25.1533, and 25.1587.
42.3.2 Explanation.
The sections of part 25, referenced above, require accounting for the effects of runway gradient. Typically, performance limitations and information are determined for runway gradients up to ±2 percent in the AFM expansion of test data. Though these gradient extremes are adequate for addressing the majority of runways, there are a number of airports frequented by transport category airplanes that have runway slopes greater than ±2 percent. Consequently, approvals have been granted for operations on runways with slopes exceeding ±2 percent with specific testing and analysis validation for the effects of the higher slopes. Additional concerns, beyond runway slope effect on acceleration and braking and proper accounting of elevations during obstacle clearance analysis, include takeoff flare from liftoff to 35 feet, minimum takeoff climb gradients, minimum 42-6
approach and landing climb gradients, landing flare distances, and unique operating procedures.
42.3.3 Procedures.
42.3.3.1 Takeoff Flare from Liftoff to 35 Feet.
The AFM expansion of the takeoff data should account for the effect of the runway slope on the portion of the takeoff distance after liftoff. At climb performance-limiting thrust-to-weight ratios, the average gradient of climb will be on the order of 2.0 to 3.0 percent. On a downhill runway of sufficient magnitude, the airplane could attain a height of 35 feet above the runway and have a positive gradient of climb relative to it, but its flight path may continue to descend beyond that point. The transition from liftoff to climbing flight, in the sense of an ascending flight path, should be adequately addressed with respect to obstacle clearance analysis data.
42.3.3.2 Minimum Takeoff Climb Gradients.
At limiting thrust-to-weight ratios, the transition to free air (i.e., out of ground effect) takeoff climb could result in steep uphill runways rising faster than the airplane’s ability to climb. The minimum second segment takeoff climb gradient should maintain the same margin, relative to the increased maximum uphill runway slope, that exists between the minimum gradient specified in § 25.121 and a two percent uphill runway.
42.3.3.3 Minimum Approach and Landing Climb Gradients.
Balked landing go-arounds, at climb limited landing weights, could also result in an uphill runway rising faster than the airplane’s ability to climb.
The minimum approach and landing climb gradients should maintain the same margins, relative to the increased maximum uphill runway slope, that exist between the minimum gradients specified in §§ 25.119 and
25.121 and a two percent uphill runway.
42.3.3.4 Landing Technique and Distance.
Final approaches to steep uphill runways will require early flare initiation, to avoid hard landings, and landing flare air distances will be increased for approaches to steep downhill runways using normal approach descent angles. The AFM operating procedures should describe any special piloting technique required for landing on steep runways. The AFM expansion of landing distances should account for the effect of runway gradient, including any expected increase in flare distances, from 50 feet to touchdown, for steep downhill runways.
42.3.3.5 Operating Procedures.
Operating procedures should be provided in the AFM for operations on runways with gradients greater than ±2 percent. Guidance should be provided on takeoff rotation and landing flare techniques.
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42.3.3.6 Operational Considerations.
For runway slopes greater than ±3 percent, the specific airport(s) should be investigated relative to runway lengths and surrounding terrain and obstacles. Airport-specific operating limitations may be necessary, such as: direction of takeoff and landing, takeoff flap restrictions, prohibition of overspeed takeoffs on downhill runways, requirement for the anti-skid system to be operative and on, and restrictions on engine bleed air and power extraction.
42.3.3.7 Flight Test Requirements.
For approval of certification data for runway slopes exceeding ±3 percent, operational flight tests should be conducted to verify the proposed procedures and performance information.
42.4 Criteria for Approval of Steep Approach to Landing.
42.4.1 Applicable Regulations.
Sections 25.119, 25.121, 25.125, and 25.143.
42.4.2 Explanation.
42.4.2.1 Airworthiness Approval.
The standard approach angle assumed as part of the type certification of transport category airplanes is 3°, which coincides with the nominal ILS approach angle. Those evaluations are considered adequate to address approach angles of less than 4.5°. The criteria listed below represent FAA policy for airworthiness approval of steep approach landing capability using an approach angle of 4.5° or more. Additions or deletions to these criteria may be needed to address specific design features. It should be noted in the AFM that the presentation of the steep approach limitations, procedures, and performance information reflects the capability of the airplane to perform steep approaches but does not constitute operational approval.
42.4.2.2 Operational Approval.
Operational approval to conduct steep approaches in the United States is the exclusive responsibility of FAA Flight Standards Service and cannot be delegated to FAA Aircraft Certification Service employees, designees, or to foreign civil aviation authorities. FAA Flight Standards Service has assigned this responsibility to the Flight Standardization Board (FSB) with oversight for the airplane type in question. Operational approval will, in part, be based on the results of the airworthiness testing described in this section. Additional testing, for operational concerns, may be combined with the airworthiness testing. Ideally, the testing for operational approval 42-8