Section 10. FIRE PROTECTION (RESERVED)
Section 11. MISCELLANEOUS (RESERVED)
CHAPTER 5 - POWERPLANT Section 1. GENERAL
89. INSTALLATION - § 25.901 . [RESERVED]
90. ENGINES - § 25.903 .
a. Engine Isolation - § 25.903(b) .
(1) Explanation. Approval of Engine Isolation Criteria - The powerplants, and all systems controlling or influencing the performance of the powerplants, must be arranged and isolated from each other to allow operation, in at least one configuration, so that a failure of any engine or any said system will not:
(i) Prevent the continued safe operati on of the remaining engines; or
(ii) Require immediate action by any crewmember for continued safe operation.
(2) Procedures .
(i) Automated control functions incorporated to reduce crew workload, which impact the engine operation and control, may require flight tests to demonstrate the effects of various simulated failures, including engine surging and single engine failures. Failures in systems such as the auto-throttles, digital flight guidance computers, engine synchronizers, and electronic engine controls may need to be simulated to ensure that surging or a failure in one engine system will not hazardously affect control and operation of the remaining engine systems.
Such failure simulations may include disruption of electrical power to selected control components, as well as simulated engine failures (throttle chops).
(ii) The applicant should submit a comprehensive test plan detailing the test conditions and failure modes to be simulated. Careful consideration should be given to conducting these tests at safe altitudes and airspeeds, since results of the failure simulations may not be entirely predictable. Where possible, without compromising tests results, on-aircraft (i.e., installed engines) tests of this type should be accomplished on the ground.
b. Control of Engine Rotation - § 25.903(c) .
(1) Explanation. Section 25.903(c) requires that a means be provided to stop the rotation of any individual engine in flight. An exclusion is provided for turbine engines whereby a means to stop rotation need only be provided in cases where continued rotation could jeopardize the safety of the airplane. If means are not provided to completely stop the rotation of turbine engines, it should be shown that continued rotation, either windmilling or controlled, of a shut down turbine engine will not cause:
(i) Powerplant (including engine and accessories) structural damage that will adversely affect other engines or the airplane structure;
(ii) Flammable fluids to be pumped into a fi re or into an ignition source; or
(iii) A vibration mode that will adversely affect the aerodynamic or structural integrity of the airplane.
(2) Procedures . None.
c. Turbine Engine Installations - § 25.903(d) .
(1) Explanation. Section 25.903(d) presents specific concerns related to turbine engine installations.
The requirements presented in § 25.903(d)(2) are intended to ensure that the installed powerplant control devices, systems, and instrumentation will reasonably protect against exceeding engine operating limitations that adversely affect turbine rotor integrity.
(2) Intermixing of Engines . Engines with different ratings, and/or with different cowls, may be intermixed on airplanes, provided the proper limitations and performance information associated with the engine combination are used. In general, for four-, three-, or two-engine airplanes, the performance combination is as follows:
(i) When one lower thrust engine is installed, the normal Airplane Flight Manual (AFM) performance level is reduced by an increment appropriate to the decrease in thrust resulting from the intermix.
(ii) When more than one lower thrust engine is installed, the AFM performance should be based on the thrust of the lower/lowest rated engine.
(iii) The minimum control speeds (V MCG, VMCA & VMCL) must be based on the highest thrust engine(s).
(iv) The operating procedures must be provided for all engines installed (i.e., airstart altitude/airspeed envelopes, crew responses to engine warning systems, etc.). Differences in operating methods shall be limited to the equivalent of having a maximum of two different engines on the airplane.
(v) A maximum of two takeoff thrust settings (EPR or N 1) are permitted for airplanes with intermixed engines; this includes differences related to air conditioning pack and compressor bleed configurations.
(vi) A placard, identifying the location of the non-standard engine type, must be installed. All engine limits and instrument markings should be appropriate to the engine installed at each location. EPR, N 1, N2, EGT, etc. limits for each engine, or the ratings at which they will be operated, must be properly presented to the pilot in accordance with §§ 25.1541 and 25.1543 and Part 121 of the FAR.
d. Engine Restart Capability - § 25.903 (e) .
(1) Explanation.
(i) Approval of Engine Restart Capability . An altitude and airspeed envelope must be established by the applicant for in-flight engine restarting, and means provided to restart each engine in flight within this envelope.
(ii) Engine Restart Envelope . For turbojet and early turbofan engines with low bypass ratios (approximately one), inflight restart capability was generally provided by " windmilling" of the engine. The windmilling airflow through these engines was capable of providing enough rotational energy to permit inflight restarting throughout most of the approved airspeed-altitude operating envelope. From the experience gained with these first generation engines, acceptable restart capability has been established as 30 seconds from "FUEL ON" to ignition, and 90 seconds from "IGNITION" to stabilized idle. The 90 second ignition to idle time upper limit is based on the ability of the flightcrew to perceive the progression of the engine start by monitoring the time rate-ofchange of N2 and exhaust gas temperature. As bypass ratios increased, and rotational energy requirements increased, the " windmilling" restart envelopes became smaller. Some higher bypass ratio engines require an assist from an auxiliary pneumatic source, such as bleed air from an operating engine or an inflight operable Auxiliary Power Unit (APU), to provide restart capability over a large portion of the airplane operating envelope. Turboprop engines, particularly those with free-turbines, also require some sort of "auxiliary" start assist; this is generally provided by an electric starter or, in some cases, an inflight operable APU. Engine restart envelopes should clearly distinguish between the areas of different restart capabilities in terms of time to restart, windmilling only restart, and auxiliary air assisted restart. If an APU is required for restart over a significant portion of the operating envelope, a separate inflight start envelope should be substantiated by flight test for the APU in the "cold-soaked" condition associated with medium to high altitude cruise conditions. Engine and APU (if applicable) restart envelopes, and related procedures, should be included in the limitations section of the Airplane Flight Manual.
(iii) All-Engine Restart Capability . As technological advancements increased specific engine thrust output with a simultaneous decrease in specific fuel consumption, and wing designs produced greater lift, the number of engines required for a given airplane weight has decreased to the point where the majority of modern
transport category airplanes are equipped with just two engines. Service history has recorded a number of inflight all-engine thrust loss incidents from various causes: flameouts from inclement weather conditions, volcanic ash ingestion, fuel nozzle coking, fuel contamination and several cases of flightcrew fuel mismanagement. These incidents have occurred during takeoff climbout and in high altitude cruise. Consequently, it should be substantiated by flight test that restart capability exists following the inflight shutdown of all engines. This should be demonstrated for the momentary shutdown from a high power setting, associated with the takeoff and climb flight regimes, and the extended shutdown at medium to high altitude where the engines may be " windmilling" and/or "cold soaked."
(2) Procedures .
(i) Tests should be conducted to determine that inflight restarting can be accomplished within the envelope provided. Restarts at the conditions of the critical corners of the envelope and at or near the high altitude extremes of the envelope should be conducted to verify the boundary conditions of the envelope.
(ii) Inflight engine restart capability should also be evaluated with regard to suction feed climb conditions at the minimum suction feed relight altitude, and loss of normal AC power (Ref. § 25.1351(d)).
(iii) The engine operating characteristics should be evaluated during each restart. In par ticular, any tendencies for the engine to surge, dwell for abnormally long periods below idle, or produce other unusual vibration or audible noises should be noted.
(iv) To address the dual engine flameout case during takeoff and initial climb-out, wit h the engines initially at maximum climb thrust (or higher), it should be demonstrated that the test engine will accelerate to the initial power setting after a brief shutdown (up to 15 seconds), when the fuel source is restored.
(v) To address dual en gine flameout at high altitude (greater than 20,000 feet), it should be shown, by a combination of flight test and analysis, that the engines can be restarted, and the airplane's descent arrested, with a total altitude loss of not more than 5000 feet. Additionally, engine restart should be accomplished prior to exceeding 300 knots IAS.
(vi) If an onboard auxiliary power unit (APU) is required to provide power assist for inflight engine restart, the minimum APU start reliability should be determined, and its operation evaluated by flight tests in critical portions of the flight envelope.
(vii) If start cartridges are used to provide restart capability, they should be of sufficient capacity (or number) to provide at least two start attempts for each engine.
(viii) The inflight engine restart envelope presented in the Airplane Flight Manual (AFM) should identify a "core windmill relight envelope" that will provide engine ignition within 30 seconds and stabilized idle within 90 seconds of restart initiation. A larger envelope, which includes appropriately labeled longer restart times, may be allowed if it can be shown that indication of a clear progression of engine start is provided to the flightcrew.
The AFM should also contain the restart procedures appropriate to each phase of flight (i.e. low altitude "hot start," high altitude "cold soaked" start, etc.).
91. AUTOMATIC TAKEOFF THRUST CONTROL SYSTEMS (ATTCS) - § 25.904 .
a. Explanation.
(1) Beginning in the 1970's, some manufacturers of tu rbojet powered airplanes elected to equip their airplanes with engine thrust control systems that automatically increased the thrust on the operating engine(s) when any engine failed. A similar system, referred to as an Automatic Takeoff Power Control System, was subsequently installed on turbopropeller airplanes.
(2) Takeoff performance credit was granted for ATTCS based upon prescribed system functional and reliability requirements, and performance related restrictions (e.g., initial takeoff thrust must not be less than 90 percent of that set by the ATTCS).
(3) These systems represented "novel or unusual design features" not adequately addressed by the requirements of Part 25 at the time. Consequently, the airworthiness requirements for the early ATTCS certifications were prescribed in special conditions in accordance with § 21.16. The regulatory and technical content of those special conditions was added to Part 25 as § 25.904 and Appendix I by Amendment 25-62.
b. Procedures . Certification of an airplane with an ATTCS requires flight test demonstration of certain performance and functional aspects of the system, as outlined below:
(1) Takeoff speeds, as limited by V MCG and VMCA, must reflect the effect of ATTCS operation following failure of the critical engine. It is permissible to publish two sets of takeoff performance data: one for ATTCS unarmed and one for ATTCS armed. In such cases, the AFM limitations, operating procedures, and performance information should clearly differentiate between the two sets of performance data.
(2) Engine operating characteristics should be investigated during operation of the ATTCS, and with the operating engines at the steady-state maximum thrust level achieved following operation of the ATTCS. (Refer to the guidance material provided in paragraph 99 of this Advisory Circular.)
(3) Manual override of the ATTCS should be verified in flight test. This capability has been provided by the ability of the pilot to push the throttle levers to a higher thrust setting, for airplanes that use less than "fullthrottle" for takeoff, and by activating an override switch for "firewall-type" fuel control systems. In the case of the override switch, it must be located on or forward of the power levers, and it must be easily accessible to the pilot's hand that normally controls the power lever position. It should also be demonstrated that the thrust/power level can be manually decreased at any time following ATTCS operation.
(4) A critical time period must be de termined during which the probability of concurrent engine and ATTCS failure must be shown to be extremely improbable (not greater than 10 -9 per flight hour). This critical time period is defined in Appendix I to Part 25 as being from one second before the airplane attains V 1, to a time where the actual takeoff flight path (i.e., no gradient reductions), following a simultaneous engine and ATTCS failure, would intersect the normal (i.e., engine failure at V EF and no ATTCS) one-engine-inoperative actual takeoff flight path at no less than 400 feet above the takeoff surface. The probability of failure of the automatic takeoff thrust control system, itself, must be shown to be improbable (not greater than 10 -5 per flight hour).
(5) Performance credit for a n operating ATTCS is not to be taken when operations are conducted using reduced takeoff thrust methods. If the ATTCS is armed during reduced thrust takeoffs, the relevant takeoff speeds must meet the required controllability criteria of part 25 at the thrust level provided by operation of the ATTCS. It must be demonstrated that the airplane has no adverse handling characteristics and the engine(s) must not exhibit adverse operating characteristics or exceed operating limits when the ATTCS operates.
(i) The Airplane Flight Manual (AFM) must contain information, instructions, and procedures, as required, regarding the peculiarities of normal and abnormal operations when scheduling reduced thrust operations with an armed ATTCS.
(ii) Takeoff with an armed ATTCS is not restricted when airplane performance is based on an approved “ derate” thrust rating that has corresponding airplane and engine limitations approved for use under all weight, altitude, and temperature (WAT) conditions.
92. PROPELLERS - § 25.905 .
a. Explanation. When an automatic control system for simultaneous RPM control of all propellers is installed, it should be shown that no single failure or malfunction in this system or in an engine controlling this system, will:
(1) Cause the allowable engine overspeed for this condition to be exceeded at any time.
(2) Cause a loss of thrust that will cause the airplane to descend below the takeoff path, established in accordance with § 25.111, if such a system is certificated for use during takeoff and climb. This should be shown
for all weights and altitudes for which certification is desired. A period of five seconds should be allowed from the time the malfunction occurs to the initial motion of the cockpit control for corrective action taken by the crew.
b. Procedures . Compliance with this policy may be shown by analysis, flight demonstration, or a combination of analysis and flight demonstration.
[93. - 94.] [RESERVED]
95. PROPELLER DEICING - § 25.929 .
a. Explanation. None.
b. Procedures . If the propellers are equipped with fluid type deicers, the flow test should be conducted starting with a full tank of fluid and operated at maximum flow rate for a time period ( ≈15 min.) found operationally suitable. The operation should be checked at all engine speeds and powers. The tank should be refilled to determine the amount of fluid used after the airplane has landed.
96. REVERSING SYSTEMS - § 25.933 .
a. Turbojet Reversing Systems - § 25.933(a) .
(1) Explanation.
(i) For reversers intended to be operable on the ground only, it must be shown that the airplane can be safely landed and stopped with a critical engine reverser deployed. In addition, if an undamaged reverser inadvertently becomes deployed in flight, it must be shown that it can be safely restored to a forward thrust position.
(ii) For turbojet reversing systems intended for ground and/or inflight use, it must be shown that unwanted deployment of a critical reverser under normal operating conditions will not prevent continued safe flight and landing. Flight tests may be required to obtain aerodynamic data with the critical reverser deployed, to confirm that its deployment in the normal operating envelope will not be catastrophic to the airplane.
(2) Procedures .
(i) Turbine engine thrust reversers may be approved provided the following basic criteria are met:
(A) Exceptional piloting skill is not required in taxiing, or in any condition in which reverse thrust is to be used.
(B) Necessary operating procedures, operating limitations, and placards are established.
(C) The airplane control characteristics are satisfactory with regard to control forces encountered.
(D) The directional control is adequate using normal piloting skill. This is of particular importance for airplanes with aft-mounted engines, which may experience a loss of rudder effectiveness with reverse thrust. This may result in reductions in maximum reverse thrust levels (i.e., lower EPR or N 1 settings) and/or increases in reverse thrust minimum operational speeds. The stabilizing effect of the nose gear should also be investigated, particularly for the one-engine inoperative use of reverse thrust on wet runway surfaces.
(E) A determination is made that no dangerous condition is encountered in the event of the sudden failure of one engine in any likely reverse thrust operating condition throughout the airplane's approved operating envelope.
(F) The operating procedures and ai rplane configuration are such as to provide reasonable safeguards against engine foreign object ingestion and serious structural damage to parts of the airplane due to the reverse airflow. This is normally accomplished by specifying in the limitations section of the Airplane Flight Manual a minimum airspeed at which the thrust reversers must be retracted.
(G) It is determined that the pilot's vision is not dangerously obscured under normal operating conditions on dusty or wet runways and where light snow is on the runway.
(H) For seaplanes, it is determined that the pilot's vision is not dangerously obscured by spray due to reverse airflow under normal water operating conditions.
(I) The procedure and mechanisms for reversing should provid e a reverse idle setting such that, without requiring exceptional piloting skill, at least the following conditions are met:
(1) Sufficient power is maintained to keep the engine running at an adequate speed to prevent engine stalling during and after the reversing operation.
(2) The engine does not overspeed or stall during and after the reversing operation.
(3) The engine cooling characteristics should be satisfactory in any likely operating condition.
(J) For airplanes equipped with thrust reversers intended for inflight use, the effect of nondeployment of a reverser (i.e., asymmetric deployment) on airplane controllability should be investigated.
(ii) For the failed reverser demonstration tests, the following criteria are provided:
(A) The landing with a reverser deployed should be conducted with a flap setting and an airspeed such that a landing can be accomplished safely and consistently. The conditions and operating procedures to use when the landing is made with the deployed reverser must be defined and incorporated in the AFM per §
25.1585(a)(9).
(B) The restow test should be conducted at a reasonable and safe altitude and at an airspeed where the airplane can be safely controlled (approximately 200 knots). A procedure should be developed so that the reverser can be restowed (if undamaged) safely, without causing unacceptable airplane controllability problems.
The restowing procedure, airspeed, and airplane flight controls configuration must be incorporated in the AFM.
(3) Aircraft Backing Using Reverse Thrust . Limited operational approvals have been granted for the use of thrust reverser systems to back away from terminal gates in lieu of a tug pushback. These approvals are granted by the cognizant FAA Flight Standards office for each operator, the approval consisting of an amendment to the operator's Operations Specifications identifying the airplane type, the airport, and the specific gates at that airport at which reverse thrust backing may be used. Though reverse thrust backing is not specifically an airworthiness approval item, there are certain areas of concern that overlap airworthiness and operations. (These items are addressed in paragraph 242 of this AC.)
b. Propeller Reversing Systems - § 25.933(b) .
(1) Explanation. None.
(2) Procedures . Reverse thrust propeller installations may be approved, provided the following is acceptable:
(i) A reliable means for preventing the inflight selection of a power setting below flight idle is provided.
(ii) Exceptional piloting skill is not required in taxiing or in any condition in which reverse thrust is to be used.
(iii) Necessary operating procedures, operating limitations, and placards are established.
(iv) The airplane cont rol characteristics are satisfactory with regard to control forces encountered.
(v) The directional control is adequate using normal piloting skill.
(vi) A determination is made that no dangerous condition is encountered in the event of sudden failure of one engine in any likely operating condition.
(vii) The operating procedures and airplane configuration are such as to provide reasonable safeguards against serious structural damage to parts of the airplane due to the direct effects of the reverse airflow or any resultant buffeting.
(viii) It is determined that the pilot's vision is not dangerously obscured under normal operating conditions on dusty or wet runways and where light snow is on the runway.
(ix) It is determined that the pi lot's vision is not dangerously obscured by spray due to reverse airflow under normal water operating conditions with seaplanes.
(x) The procedure and mechanisms for reversing should provide a reverse idle setting such that without requiring exceptional piloting skill at least the following conditions are met:
(A) Sufficient power is maintained to keep the engine running at an adequate speed to prevent engine stalling during and after the propeller reversing operation.
(B) The propeller does n ot exceed the approved speed limit of 14 CFR part 35 or the airplane-manufacturer-declared propeller speed limit during and after the propeller reversing operation.
(C) This idle setting does not exceed 25 percent of the maximum continuous rating.
(xi) The engine cooling characteristics should be satisfactory in any likely operating condition.
97. TURBOJET ENGINE THRUST REVERSER SYSTEM TESTS - § 25.934 . [RESERVED]
98. TURBOPROPELLER-DRAG LIMITING SYSTEMS - § 25.937 .
a. Explanation. Approval of Automatic Propeller Feathering Systems . All parts of the feathering device that are integral with the propeller, or attached to it in a manner that may affect propeller airworthiness, should be considered from the standpoint of the applicable provisions of 14 CFR part 35 of the Federal Aviation Regulations (FAR). The determination of the continuing eligibility of the propeller under the existing type certificate, when the device is installed or attached, will be made on the following basis:
(1) The automatic propeller feathering system should not adversely affect normal propeller operation and should function properly under all temperature, altitude, airspeed, vibration, acceleration, and other conditions to be expected in normal ground and flight operation.
(2) The automatic device should be demonstrated to be free from malfunctioning which may cause feathering under any conditions other than those under which it is intended to operate. For example, it should not cause feathering during:
(i) Momentary loss of power; or
(ii) Approaches with reduced throttle settings.
(3) The automatic propeller feathering system should be capable of operating in its intended manner whenever the throttle control is in the normal position to provide takeoff power. No special operations at the time of engine failure should be necessary on the part of the crew in order to make the automatic feathering system operative. (See also §§ 25.101, 25.111, 25.121 and 25.1501.)
(4) The automatic propeller featherin g system installation should be such that not more than one engine will be feathered automatically, even if more than one engine fails simultaneously.
(5) The automatic propeller feathering system installation should be such that normal operation may be regained after the propeller has begun to feather automatically.
(6) The automatic propeller feathering system installation should incorporate a switch, or equivalent means, by which to make the system inoperative.
b. Procedures .
(1) Propeller Feathering System Operational Tests .
(i) Tests should be conducted to determine the time required for the propeller to change from windmilling (with the propeller controls set for takeoff) to the feathered position at the takeoff safety speed, V 2.
(ii) The propeller feathering system should be tested to demonstrate non-rotation or as a minimum, non-hazardous rotation at up to 1.2 times the maximum level flight speed, with one engine inoperative or the speed employed in emergency descents, whichever is higher, with:
(A) The critical engine inoperative;
(B) Wing flaps retracted;
(C) Landing gear retracted; and (D) Cowl flaps (if applicable) closed.
(iii) A sufficient speed range should be covered to assure that the propeller feathe ring angle, established on the basis of the high speed requirement, will not permit hazardous reverse rotation at the lower speeds. In addition, the propeller should not inadvertently unfeather during these tests.
(iv) In order to demonstrate that the feathering system operates satisfactorily, the propeller should be feathered and unfeathered at the maximum operating altitude established in accordance with § 25.1527. The following data should be recorded:
(A) Time to feather the propeller at the one-engine-inoperative cruising speed;
(B) Time to unfeather the propeller to the minimum declared governing speed at maximum operating altitude (note that some driftdown may occur) and one-engine-inoperative cruising speed;
(C) Altitude of prope ller feathering tests; and (D) Ambient air temperature of propeller feathering tests.
(v) In order to demonstrate that the feathering system operates satisfactorily, the propeller should be feathered at the condition within the airplane operating envelope that is critical for the propeller.
99. TURBINE ENGINE OPERATING CHARACTERISTICS - § 25.939(a) .
a. Explanation. The turbine engines of a transport category airplane must continue to operate safely during normal and emergency operation within the range of operating limitations of the airplane. Generally, compliance with § 25.939(a) can be determined to some extent while ascertaining compliance with other Part 25 requirements, such as performance, controllability, maneuverability, and stall speed characteristics. Turbine engines should be stable in their operation and run free of adverse characteristics throughout the normal flight envelope. Certain adverse characteristics are allowed in specific flight regimes if they do not present a hazardous condition.
b. Reference. See Advisory Circular 25.939-1, "Evaluating Turbine Engine Operating Characteristics," dated March 19, 1986, for comprehensive guidance in the evaluation of turbine engine operating characteristics to show compliance with the requirements of § 25.939(a), only. The referenced advisory circular does not provide guidance for compliance with § 25.939(c), which addresses inlet compatibility.
c. Inlet Compatibility - § 25.939(c) .
(1) Explanation. Section 25.939(c) requires substantiation that the engine inlet systems on turbine engines not cause harmful vibration to the engine as a result of airflow distortion. This should be verified in both static and transient thrust conditions.
(2) Procedures . Compliance with § 25.939(c) may require special instrumentation of the inlet itself', or the engine's most critical component (i.e., fan blades). Inlet rakes permit the applicant to verify that the installed airflow distortion patterns are within the limits established by the engine manufacturer. In addition, accelerometer and/or strain gauge data could be acquired in flight tests to verify that vibration and stress level limits are not exceeded during operation in the normal flight envelope."
100. INLET, ENGINE, AND EXHAUST COMPATIBILITY - § 25.941 . [RESERVED]
101. NEGATIVE ACCELERATION - § 25.943 .
a. Explanation. Section 25.943 requires that no hazardous malfunction of an engine, auxiliary power unit (APU), or any component or system associated with their operation, should result from airplane operation at negative accelerations. A hazardous malfunction in this case is considered to be one that causes loss or sustained malfunction of the engine or APU, or improper operation of the engine accessories or systems. This requirement can be satisfied by flight test demonstrations that take into consideration the critical airplane, engine and APU configurations. The range of negative accelerations to be tested is prescribed by the flight envelope for the airplane, as defined in § 25.333. The duration of the negative acceleration excursions is intended to represent anticipated non-normal operational events such as atmospheric upsets, collision avoidance maneuvers, etc.
b. Procedures .
(1) In conducting negative acceleratio n tests, consideration should be given to engine accessory configurations, and critical levels of fuel and oil.
(2) Accelerations should be measured as close as practicable to the airplane's center of gravity position.
(3) With the engines operating at maximum continuous thrust, and the APU operating with normal load (if flight operable), the airplane should be flown at a critical negative acceleration within the flight envelope. The duration of each test condition should be a minimum of 7 seconds between 0 and -1.0g, with a total accumulation of 20 seconds of negative acceleration operation.
(4) Test data should be analyzed with regard to maintaining adequate fuel flow to the engines and APU, and maintaining lubrication of critical components.
(5) Test planning should consider that sufficient altitude be available to conduct a suction feed relight in the unlikely event of an all-engine flameout, in which case the tank pump feed lines will become uncovered and air will enter each feed line.
102. THRUST OR POWER AUGMENTATION SYSTEM § 25.945 . [RESERVED]