281 [182. - 185.] [Reserved]
Section 3. Electrical Systems and Equipment
186. General - § 25.1351.
a. Explanation. Section 25.1351(a) requires that the electrical generating capacity, and number and kinds of power sources, be determined by an electrical load analysis, and meet the requirements of § 25.1309.
b. Procedures.
(1) Section 25.1351(a) - Electrical System Capacity. Section 25.1351(a) requires the generating capacity, and number and kinds of power sources, to be determined by an electrical loads analysis and meet the requirements of § 25.1309. Additionally, verify by flight test that cooling is satisfactory to maintain component temperatures within the manufacturer’s limits, both on the ground and in flight, with the electrical system operating at maximum limit load.
(2) Section 25.1351(b)(1) - Electrical Power Configuration.
(a) Verify that electrical power sources function properly when independent and when connected in combination.
(b) For airplanes with autoland capability, verify proper electrical power reconfiguration for each available autoland mode.
(c) Verify that no hazardous airplane systems reaction occurs, to a partial loss of the electrical distribution system by simulating loss of individual busses. Simulate loss of individual busses by opening circuit breakers/relays.
(d) Verify proper transfer of electrical power between the different power sources
(i.e., external power, APU, engines).
(3) Section 25.1351(b)(2) - Failure of Power Source. Verify proper operation of system during simulated power failures by flight test functional demonstrations. The applicant must show by design analysis or laboratory demonstration, that no failure or malfunction of any power source, including the battery can create a hazard or impair the ability of remaining sources to supply essential loads.
(4) Section 25.1351(b)(3) - System Voltage and Frequency. For probable operating conditions, verify that system voltage and frequency, as applicable, at the terminals of all essential load equipment can be maintained within the limits for which the equipment is designed. This may be accomplished in a laboratory environment.
(5) Section 25.1351(b)(4) - System Transients. The applicant must show by design analysis, laboratory demonstration, and/or flight demonstration that system transients due to switching, fault clearing, or other causes during normal operations do not make essential loads inoperative, and do not cause a smoke or fire hazard. Flight test recordings may be useful to verify laboratory demonstrations of system transients and electromagnetic interference (EMI) during normal operations.
(6) Section 25.1351(b)(5) - Power Source Disconnection.
(a) Verify that there are means accessible in flight, to the appropriate crewmembers, for the individual and collective disconnection of the electrical power sources from the system.
(b) Demonstrate that the airplane can be flown with one less generator than allowed by the MMEL. Also verify that prior to switching off the non-essential electrical loads specified in the AFM, the remaining generators’ short term (up to 5 minutes) capacity is not exceeded.
(7) Section 25.1351(b)(6) - Power Source Indicators.
(a) Verify that there are means to indicate, to the appropriate crewmembers, the generating system quantities essential for the safe operation of the system, such as the voltage and current supplied by each power source, if appropriate to type of aircraft, i.e., glass cockpit design may provide information on multi-function display (MFD), electronic centralized aircraft monitor (ECAM), engine indicating and crew alerting system (EICAS), etc.)
(b) Verify proper operation of electrical power system warning, caution, and advisory indications, if any, and that these indications comply with §§ 25.1309(c) and 25.1322.
(8) Section 25.1351(c) - External Power. If provisions are made for connecting external power to the airplane, and that external power can be electrically connected to equipment other than that used for engine starting, verify that a means is provided to ensure that no external power supply having a reverse polarity, a reverse phase sequence, overvoltage, or reverse phase/neutral can supply power to the airplane’s electrical system. This demonstration may be accomplished in a laboratory environment.
(9) Section 25.1351(d) - Operation Without Normal Electrical Power. The applicant must demonstrate that the airplane can be operated safely in visual flight rules (VFR) conditions, for a period of not less than five minutes, with the normal electrical power (electrical power sources excluding the battery) inoperative, with critical type fuel (from the standpoint of flameout and restart capability), and with the airplane initially at the maximum certificated altitude.
(10) Emergency Electrical Power System.
(a) For airplanes with a type certification basis that includes Amendment 25-23, the FAA has applied a general policy that following total failure of the electrical power system, if not shown to be extremely improbable, emergency electrical power should be available to power instrument displays, systems, equipment, or parts of the airplane essential for safety of flight during IMC operations for at least 30 minutes. It may also be advisable to check that in the event when normal operation is reestablished following the use of emergency power devices, such devices can withstand, or at least do not adversely affect, the subsequent reversion to “normal” operation.
1 Thirty (30)-Minute Requirement Test. Accomplish ground and/or flight testing to verify that the main battery/non time-limited power source (e.g., auxiliary power unit (APU), ram air turbine, pneumatic or hydraulic motor, etc.) is sufficient to power the essential loads required for safety of flight during IMC operations for at least 30 minutes. If the emergency power is provided by a non time-limited power source, the main battery capacity should be sufficient for at least 5 minutes to show compliance with § 25.1351(d). Essential loads for safety of flight during IMC operations are considered to include the following:
(aa) Those essential for continued safe flight and landing during visual meteorological conditions (VMC) operations.
(bb) One display of attitude, direction, airspeed and altitude as specifically stated in § 25.1333(b), a free-air temperature indicator, and pitot/static heat capability, if required.
(cc) Communication, intercommunication, and navigation capability (for IMC operations) necessary cockpit and instrument lighting, and any other instrument displays, systems, equipment, or parts of the airplane that are necessary to safely complete the flight.
2 Perform a VMC approach and landing with the airplane powered with emergency electrical power only. Verify acceptable operation of the emergency equipment.
3 Perform a simulated night IMC approach and landing with the airplane powered with emergency electrical power only. Verify acceptable visibility and operation of the emergency equipment. This test can be accomplished on a simulator.
(b) Electrical Attitude, Altitude, Direction, and Airspeed Systems Using Battery Standby Power.
1 The FAA has published additional policy that applies to certification of flight instrument installations where: (1) all displays of any of the essential flight information
(e.g., altitude, attitude, airspeed, or direction) require electrical power; and (2) the back-up source of electrical power is time-limited. See Policy Statement PS-ANM100-2001-116, “Policy Statement with respect to All Electrical Attitude, Altitude, Direction and Airspeed Systems using Battery Standby Power,” dated April 27, 2001.
2 Flight evaluations of such installations should be used to make sure that all the essential safety related flight instrument parameters are displayed, that the pilots do not have to take any action to display them when normal power is lost, and that the standby display(s) can be effectively used for all flight tasks required for safe flight and landing.
187. Electrical Equipment and Installations - § 25.1353. [Reserved]
188. Distribution System - § 25.1355.
a. Explanation. Section 25.1355(a) defines the distribution system, including the distribution busses, their associated feeders, and each control and protective device.
b. Procedures. Section 25.1355(c) - Independent Power Sources. For equipment or systems that are required to have two independent sources of electrical power, verify by airplane demonstration that in the event of a failure of one power source for such equipment or system, another power source (including its separate feeder) is automatically provided or can be manually selected to maintain equipment or system operation.
189. Circuit Protective Devices - § 25.1357. [Reserved]
190. Electrical System Tests - § 25.1363.
a. Explanation. Laboratory tests are conducted to verify that the control, regulation, protection, and automatic operation of the electrical system comply with §§ 25.1351 through
25.1357. Laboratory tests must be conducted on a mockup using the same type and length of feeder wires, and generating equipment that will be installed in the airplane. Additionally, the generator drives must simulate the actual prime movers on the airplane with respect to their reaction to generator loading, including loading due to faults. Section 25.1363(b) states that for each flight condition that cannot be adequately simulated in the laboratory or by ground tests on the airplane, a flight test must be conducted.
b. Procedures. Negative Acceleration Performance - Verify that no hazardous malfunctions of the electrical power system occur when the airplane is operated at the negative accelerations within the flight envelope prescribed in § 25.333. This should be shown for the greatest duration expected for the acceleration. This test is normally conducted in conjunction with the engine negative acceleration test to comply with § 25.943.
285 Section 4. Lights
191. Instrument Lights - § 25.1381.
a. Explanation. None.
b. Procedure. Under actual or simulated nighttime conditions, evaluate instrument lighting for the following characteristics:
(1) Illumination of adequate intensity is provided for all appropriate cockpit instruments/controls/equipment.
(2) Illumination is of appropriate color, intensity is evenly distributed, and is free of objectionable flicker, glare, or reflection.
(3) Dimming capability allows smoothly adjustable illumination intensity between appropriate limits.
192. Landing Lights - § 25.1383.
a. Explanation. None
b. Procedure. The landing lights should be evaluated to determine that they:
(1) Are aimed properly, provide sufficient intensity to facilitate night landings, and are acceptable at different pitch attitudes during landing approach with various c.g., flap settings and airspeed;
(2) Are not a source of objectionable glare or halation; and
(3) Are functional in MMEL configurations and during operations in adverse weather.
193. Position Light System Installation - § 25.1385.
a. Explanation. Section 25.1385(a) requires the position light system to comply with detailed technical specifications contained in §§ 25.1387 through 25.1397. These sections define location, color, visibility, and intensity requirements with considerable precision. An in depth examination of the installed position light system with regard to these requirements is not necessarily considered appropriate or within the scope of a flight test evaluation, unless it becomes apparent while accomplishing the following procedures that further examination is warranted.
b. Procedures.
(1) Operate the position light system. Verify that general locations and color are as prescribed in § 25.1385(b) and (c).
(2) Verify that position light illumination does not cause objectionable glare to the flightcrew.
[194. - 200.] [Reserved]
201. Anti-Collision Light System - § 25.1401.
a. Explanation.
(1) Section 25.1401(a)(2) requires the anti-collision light system to comply with the detailed specifications contained in § 25.1401(b) through (f). These sections define coverage, color, flash rate, and intensity requirements with some precision. An in depth examination of the installed anti-collision system, with regard to all of these requirements, is not necessarily considered appropriate or within the scope of a flight test evaluation, unless it becomes apparent while accomplishing the following procedures that further examination is warranted.
(2) Policy statement ANM-111-06-001, “Modifications Which Impact Airplane Exterior Lighting,” dated May 14, 2007, specifies that applicants need to perform an analysis for airplane modifications involving external antenna installations in order to evaluate compliance to § 25.1401. The analysis should include an evaluation of the impact of the new installation on the anticollision light system and its associated master minimum equipment list (MMEL) dispatch relief.
b. Procedures.
(1) Operate the anti-collision light system. Verify that one or more red or white lights are installed in locations that appear to provide the required visibility and which flash at the appropriate rates.
(2) Verify that the anti-collision lights are not a source of objectionable glare or halation, to the flightcrew.
(3) Evaluate anti-collision lights during flight in clouds.
202. Wing Icing Detection Lights - § 25.1403.
a. Explanation. If the airplane is intended to be certificated for night flight into known icing conditions, a means for visually or otherwise determining the extent of icing on critical surfaces must be provided.
b. Procedures. The wing icing detection lights, if required, should be evaluated to determine that they:
(1) Are aimed properly toward the appropriate surfaces, and are of sufficient intensity for required illumination.
(2) Are not a source of objectionable glare, reflection, or halation.
Section 5. Safety Equipment
[203. - 207.] [Reserved]
Section 6. Miscellaneous Equipment
208. Electronic Equipment - § 25.1431.
a. 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:
(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 must be able to continue to supply power loads under probable critical operating combinations and for probable durations;
(2) Section 25.1351(b) (Electrical systems and equipment-- General), which requires that electrical generating systems must 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
(3) Section 25.1353(a) (Electrical equipment and installations), which requires that electrical equipment and controls must 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.
b. Procedures.
(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
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.