288 frequencies above 55 Hz for stroke symbology or non-interlaced raster and 30/60 Hz 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.
(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 can be accomplished by observing the operation of flight essential equipment while:
(a) 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).
(b) 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
(c) Any other high-current airplane system that would normally be operated during flight.
[209. - 215.] [Reserved]
216. Equipment Standards for Oxygen Dispensing Units - § 25.1447.
a. Explanation.
(1) Section 25.1447(c)(2)(i) requires that each flight crewmember 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.
(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:
(a) The average time to don the mask should indicate that the five-second requirement is met.
(b) Even if the average donning time is five seconds or less, it may take longer than five seconds to don the mask for 50 percent or more of the tests. Therefore, it is also important to establish a
289 criterion regarding the distribution of test results in order to ensure that the mask can be consistently donned within five seconds.
b. Procedures.
(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 conducted in an airplane, a simulator, or a flight deck mockup that accurately reflects the proposed design.
(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.
(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.
(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.
(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.
(6) For each donning test:
(a) At least 80 percent of the donning events should be completed in five seconds or less.
(b) The average time for each donning test should be five seconds or less.
[217. - 223.] [Reserved]
Chapter 7 - Operating Limitations and Information.
Section 1. General. [Reserved]
Section 2. Operating Limitations [Reserved]
Section 3. Markings and Placards [Reserved]
Section 4. Airplane Flight Manual
224. General - § 25.1581.
a. 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.
(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.
(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.
(3) The manufacturer or operator may include other “unapproved” data in a separate and distinctively identified portion of the AFM.
b. Reference. See AC 25.1581-1, Change 1, “Airplane Flight Manual,” dated October 16, 2012, for detailed guidance on the required content and general structure of the AFM.
[225. - 227.] [Reserved]
291 Chapter 8 - Airworthiness: Miscellaneous Items
228. Design and Function Of Artificial Stall Warning and Identification Systems.
a. Applicable Regulations. Sections 25.103, 25.201, 25.203, and 25.207.
b. 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 29 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.
c. Arming and Disarming.
(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.
(a) 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-of-attack (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 highenergy rejected takeoffs have 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.
(b) 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
292 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.
(2) Stall identification systems should be armed any time the airplane is in flight.
(a) 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 228e, below.
(b) 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.
(c) 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.
(d) 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 increased exposure to malfunctions and failures, would not warrant the use of a stall identification system for configurations where it is not required.
d. Indicating and Warning Devices.
(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.
(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.
(3) A clear and distinctive cockpit indication should be given when the stall identification system has been deactivated by the flightcrew (see paragraph 228c(2)(c), above).
This indication should be present as long as the system is deactivated.
(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.
e. 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.
(1) Reliability. Probability of artificial stall warning and stall identification systems not operating when required:
(a) 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.
(b) 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.
(c) 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.
(2) Safety. Probability of artificial stall warning and stall identification systems operating inadvertently.
(a) 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.
(b) 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:
1 No single failure will result in inadvertent operation of the stall identification system; and
2 The probability of inadvertent operation from all causes is improbable (not greater than 10-5 per flight hour).
(c) Stall identification systems should be designed so that flight in turbulence will not result in inadvertent operation.
NOTE: In making the assessments of subparagraphs (d), (e) and (f), 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.
(d) 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.
(e) 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).
(f) 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, per § 25.1309(b)(1), the probability of inadvertent operation must be extremely improbable. Inhibition of the 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.
f. System Functional Requirements.
(1) Operation of the stall identification system should reduce the airplane’s angle-ofattack far enough below the point for its activation that inadvertent return to the stall angle-ofattack is unlikely.
(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 pounds applied virtually instantaneously has previously been accepted as providing this characteristic.
(3) Normal operation of the stall identification system should not result in the total normal acceleration of the airplane becoming negative.
(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.
g. System Tolerances. See paragraph 29i 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 29f(2)(f) 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).
229. Reduced and Derated Power or Thrust Takeoff Operations.
a. 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:
(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 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.
(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 (EPR) 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.
(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.
b. 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, “Reduced and Derated Takeoff Thrust (Power) Procedures,” dated May 4, 1988.
230. Runway Gradients Greater Than ± 2 Percent.
a. Applicable Regulations. Sections 25.105, 25.115, 25.119, 25.121, 25.125, 25.1533, and
25.1587.
b. 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 approach and landing climb gradients, landing flare distances, and unique operating procedures.
c. Procedures.
(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.
(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.
(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.
(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
297 runway gradient, including any expected increase in flare distances, from 50 feet to touchdown, for steep downhill runways.
(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.
(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 antiskid system to be operative and on, and restrictions on engine bleed air and power extraction.
(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.
231. Criteria For Approval Of Steep Approach To Landing.
a. Applicable Regulations. Sections 25.119, 25.121, 25.125, and 25.143.
b. Explanation.
(1) Airworthiness Approval. The standard approach angle assumed as part of the type certification of transport category airplanes is 3 degrees, which coincides with the nominal ILS approach angle. Those evaluations are considered adequate to address approach angles of less than 4.5 degrees. The criteria listed below represent FAA policy for airworthiness approval of steep approach landing capability using an approach angle of 4.5 degrees 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.
(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 would be conducted by the Flight Standardization Board during the test program for airworthiness certification of steep approach capability.
c. General Criteria.
(1) If approval is sought to conduct steep approaches in icing conditions, compliance with the part 25 requirements applicable to steep approach operations identified below should also be shown for icing conditions.
(2) The following criteria apply when showing compliance with § 25.125 for steep approaches:
(a) The airplane should be in the landing configuration used for steep approaches.
(b) Compliance with the requirement that a stable approach be conducted to a height of 50 feet with a speed not less than VREF (§ 25.125(b)(2)) should be shown with an approach path angle not exceeding the maximum for which approval is sought. The VREF used for steep approaches may be different than the VREF used for normal approaches.
(c) If the parametric method of determining the landing distance is used (see paragraph 19b(3) of this AC), approach angles should be appropriate to the steep approach path angle desired, and the touchdown sink rate for data expansion should be limited to 6 feet per second.
(3) The landing distance established under § 25.125(a) begins at a point 50 feet above the landing surface. If an applicant proposes to use a different height for the beginning of the steep approach landing distance, this must be done through an equivalent level of safety finding, in accordance with § 21.21(b)(1), or an exemption, in accordance with part 11. This has been done in some steep approach certifications to take advantage of precision approach guidance at an airport that guides the airplane to a height over the runway threshold of less than 50 feet.
(4) Compliance with §§ 25.119 and 25.121(d) should be shown using the configurations and speeds established for steep approach operations.
d. Test Conditions For Reasonably Expected Variations In Approach Speed and Path Angle.
(1) The following additional criteria should be applied to show that the airplane is safely controllable and maneuverable during landing (§ 25.143(a)(5)).
(a) Under calm air conditions, demonstrate that it is possible to complete an approach, touchdown, and stop without displaying any hazardous characteristics in the following conditions:
1 An approach path angle 2 degrees steeper than the steepest approach path angle for which approval is sought at the VREF established for a steep approach; and
2 The steepest approach path angle for which approval is sought at a speed 5 knots lower than the VREF established for a steep approach.
(b) For both conditions above:
1 The airplane should be loaded to the most critical weight and c.g.
combination;
2 The airplane should be in the steep approach configuration;
3 The rate of descent should be reduced to no more than 3 feet per second at touchdown;
4 Below a height of 200 feet, no action should be taken by the pilot to increase power or thrust, apart from those small changes needed to maintain an accurate approach;
5 After initiating the flare, the longitudinal control should not be used to depress the nose apart from those small changes necessary to maintain a continuous and consistent flare flight path;
6 The flare, touchdown, and landing should not require exceptional piloting skill, alertness, or strength; and
7 To ensure adequate capability for a go-around or down path adjustment, the engines should remain above flight idle power or thrust when stabilized on the approach path.
NOTE: The 2 degrees steeper approach path angle demonstration is to account for tailwinds on the approach and to take into account necessary corrections back to the desired approach path after inadvertent excursions. The purpose of the test at VREF minus 5 knots is to account for an unnoticed speed decrease during the approach, hence the requirement in paragraph 231d(1)(b)4 for no power or thrust increase to account for the slower speed.
(c) For flight test safety reasons, when conducting the 2 degrees steeper approach path angle test condition of paragraph 231d(1)(a)1, the pilot may begin to flare the airplane (or reduce the approach angle) at a reasonable height somewhat higher than the normal steep approach flare height. If this is done, it should be shown by analysis that there is sufficient pitch control to arrest the descent rate if the flare were to be initiated at the normal steep approach flare height, keeping in mind the criteria in paragraphs 231d(1)(b)3 and 6.
(2) Compliance with § 25.143(b)(1) should be assessed as follows: Demonstrate that the airplane can both safely land and safely transition to a go-around following a failure of the critical engine at any point in the approach under the following conditions:
(a) The steepest approach angle for which approval is sought;
(b) The VREF established for a steep approach; and
(c) The most critical combination of weight and c.g.; and