From: firstname.lastname@example.org (Robert Dorsett) Date: 04 Aug 96 16:44:51
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... relating to blade separation (from FAR 25 and FAR 33). As a bonus, I included the "bird" section. :-) The complete text of these sections is on: ftp://ftp.faa.gov/pub/files/avr/afs/fars/ =================================================== Sec. 25.571 Damage--tolerance and fatigue evaluation of structure. (a) General. An evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to fatigue, corrosion, or accidental damage, will be avoided throughout the operational life of the airplane. This evaluation must be conducted in accordance with the provisions of paragraphs (b) and (e) of this section, except as specified in paragraph (c) of this section, for each part of the structure which could contribute to a catastrophic failure (such as wing, empennage, control surfaces and their systems, the fuselage, engine mounting, landing gear, and their related primary attachments). Advisory Circular AC No. 25.571-1 contains guidance information relating to the requirements of this section (copies of the advisory circular may be obtained from the U.S. Department of Transportation, Publications Section M443.1, Washington, D.C. 20590). For turbojet powered airplanes, those parts which could contribute to a catastrophic failure must also be evaluated under paragraph (d) of this section. In addition, the following apply: (1) Each evaluation required by this section must include-- (i) The typical loading spectra, temperatures, and humidities expected in service; (ii) The identification of principal structural elements and detail design points, the failure of which could cause catastrophic failure of the airplane; and (iii) An analysis, supported by test evidence, of the principal structural elements and detail design points identified in paragraph (a)(1)(ii) of this section. (2) The service history of airplanes of similar structural design, taking due account of differences in operating conditions and procedures, may be used in the evaluations required by this section. (3) Based on the evaluations required by this section, inspections or other procedures must be established as necessary to prevent catastrophic failure, and must be included in the Airworthiness Limitations section of the Instruction for Continued Airworthiness required by Sec. 25.1529. (b) Damage-tolerance evaluation. The evaluation must include a determination of the probable locations and modes of damage due to fatigue, corrosion, or accidental damage. The determination must be by analysis supported by test evidence and (if available) service experience. Damage at multiple sites due to prior fatigue exposure must be included where the design is such that this type of damage can be expected to occur. The evaluation must incorporate repeated load and static analyses supported by test evidence. The extent of damage for residual strength evaluation at any time within the operational life must be consistent with the initial detectability and subsequent growth under repeated loads. The residual strength evaluation must show that the remaining structure is able to withstand loads (considered as static ultimate loads) corresponding to the following conditions: (1) The limit symmetrical maneuvering conditions specified in Sec. 25.337 at VC and in Sec. 25.345. (2) The limit gust condition specified in Secs. 25.305(d), 25.341, and 25.351(b) at the specified speeds up to Vc, and in Sec. 25.345. (3) The limit rolling conditions specified in Sec. 25.349 and the limit unsymmetrical conditions specified in Secs. 25.367 and 25.427, at speeds up to VC. (4) The limit yaw maneuvering conditions specified in Sec. 25.351(a) at the specified speeds up to VC. (5) For pressurized cabins, the following conditions: (i) The normal operating differential pressure combined with the expected external aerodynamic pressures applied simultaneously with the flight loading conditions specified in paragraphs (b) (1) through (4) of this section, if they have a significant effect. (ii) The expected external aerodynamic pressures in 1 g flight combined with a cabin differential pressure equal to 1.1 times the normal operating differential pressure without any other load. (6) For landing gear and directly-affected airframe structure, the limit ground loading conditions specified in Secs. 25.473, 25.491, and 25.493. If significant changes in structural stiffness or geometry, or both, follow from a structural failure, or partial failure, the effect on damage tolerance must be further investigated. (c) Fatigue (safe-life) evaluation. Compliance with the damage-tolerance requirements of paragraph (b) of this section is not required if the applicant establishes that their application for particular structure is impractical. This structure must be shown by analysis, supported by test evidence, to be able to withstand the repeated loads of variable magnitude expected during its service life without detectable cracks. Appropriate safe- life scatter factors must be applied. (d) Sonic fatigue strength. It must be shown by analysis, supported by test evidence, or by the service history of airplanes of similar structural design and sonic excitation environment, that-- (1) Sonic fatigue cracks are not probable in any part of the flight structure subject to sonic excitation; or (2) Catastrophic failure caused by sonic cracks is not probable assuming that the loads prescribed in paragraph (b) of this section are applied to all areas affected by those cracks. (e) Damage-tolerance (discrete source) evaluation. The airplane must be capable of successfully completing a flight during which likely structural damage occurs as a result of-- (1) Impact with a 4-pound bird at Vc at sea level to 8,000 feet; (2) Uncontained fan blade impact; (3) Uncontained engine failure; or (4) Uncontained high energy rotating machinery failure. The damaged structure must be able to withstand the static loads (considered as ultimate loads) which are reasonably expected to occur on the flight. Dynamic effects on these static loads need not be considered. Corrective action to be taken by the pilot following the incident, such as limiting maneuvers, avoiding turbulence, and reducing speed, must be considered. If significant changes in structural stiffness or geometry, or both, follow from a structural failure or partial failure, the effect on damage tolerance must be further investigated. [Amdt. 25-45, 43 FR 46242, Oct. 5, 1978, as amended by Amdt. 25-54, 45 FR 60173, Sept. 11, 1980; Amdt. 25-72, 55 FR 29776, July 20, 1990] ***************************************************************************** Sec. 25.1461 Equipment containing high energy rotors. (a) Equipment containing high energy rotors must meet paragraph (b), (c), or (d) of this section. (b) High energy rotors contained in equipment must be able to withstand damage caused by malfunctions, vibration, abnormal speeds, and abnormal temperatures. In addition-- (1) Auxiliary rotor cases must be able to contain damage caused by the failure of high energy rotor blades; and (2) Equipment control devices, systems, and instrumentation must reasonably ensure that no operating limitations affecting the integrity of high energy rotors will be exceeded in service. (c) It must be shown by test that equipment containing high energy rotors can contain any failure of a high energy rotor that occurs at the highest speed obtainable with the normal speed control devices inoperative. (d) Equipment containing high energy rotors must be located where rotor failure will neither endanger the occupants nor adversely affect continued safe flight. [Amdt. 25-41, 42 FR 36971, July 18, 1977] Sec. 33.19 Durability. (a) Engine design and construction must minimize the development of an unsafe condition of the engine between overhaul periods. The design of the compressor and turbine rotor cases must provide for the containment of damage from rotor blade failure. Energy levels and trajectories of fragments resulting from rotor blade failure that lie outside the compressor and turbine rotor cases must be defined. (b) Each component of the propeller blade pitch control system which is a part of the engine type design must meet the requirements of Sec. 35.42 of this chapter. Sec. 33.75 Safety analysis. It must be shown by analysis that any probable malfunction or any probable single or multiple failure, or any probable improper operation of the engine will not cause the engine to-- (a) Catch fire; (b) Burst (release hazardous fragments through the engine case); (c) Generate loads greater than those ultimate loads specified in Sec. 33.23(a); or (d) Lose the capability of being shut down. [Amdt. 33-6, 39 FR 35467, Oct. 1, 1974, as amended by Amdt. 33-10, 49 FR 6852, Feb. 23, 1984] Sec. 33.77 Foreign object ingestion. (a) Ingestion of a 4-pound bird, under the conditions prescribed in paragraph (e) of this section, may not cause the engine to-- (1) Catch fire; (2) Burst (release hazardous fragments through the engine case); (3) Generate loads greater than those ultimate loads specified in Sec. 33.23(a); or (4) Lose the capability of being shut down. (b) Ingestion of 3-ounce birds or 1 1/2 -pound birds, under the conditions prescribed in paragraph (e) of this section, may not-- (1) Cause more than a sustained 25 percent power or thrust loss; (2) Require the engine to be shut down within 5 minutes from the time of ingestion; or (3) Result in a potentially hazardous condition. (c) Ingestion of water, ice, or hail, under the conditions prescribed in paragraph (e) of this section, may not cause a sustained power or thrust loss or require the engine to be shut down. It must be demonstrated that the engine can accelerate and decelerate safely while inducting a mixture of at least 4 percent water by weight of engine airflow following stabilized operation at both flight idle and takeoff power settings with at least a 4 percent water-to-air ratio. (d) For an engine that incorporates a protection device, compliance with this section need not be demonstrated with respect to foreign objects to be ingested under the conditions prescribed in paragraph (e) of this section if it is shown that-- (1) Such foreign objects are of a size that will not pass through the protective device; (2) The protective device will withstand the impact of the foreign objects; and (3) The foreign object, or objects, stopped by the protective device will not obstruct the flow of induction air into the engine with a resultant sustained reduction in power or thrust greater than those values required by paragraphs (b) and (c) of this section. (e) Compliance with paragraphs (a), (b), and (c) of this section must be shown by engine test under the following ingestion conditions: Foreign Speed of Engine object Test quantity foreign object operation Ingestion Birds: 3-ounce size One for each Liftoff speed Takeoff In rapid 50 square of typical sequence to inches of aircraft simulate a inlet area or flock fraction encounter thereof up to and aimed at a maximum of selected 16 birds. critical Three-ounce areas. bird ingestion not required if a 1 1/2 -pound bird will pass the inlet guide vanes into the rotor blades 1 1/2 -pound One for the Initial climb Takeoff In rapid size first 300 speed of sequence to square inches typical simulate a of inlet aircraft flock area, if it encounter can enter the and aimed at inlet, plus selected one for each critical additional areas. 600 square inches of inlet area or fraction thereof up to a maximum of 8 birds 4-pound size One, if it can Maximum climb Maximum cruise Aimed at enter the speed of critical inlet typical area. aircraft if the engine has inlet guide vanes Liftoff speed Takeoff Aimed at of typical critical aircraft, if area. the engine does not have inlet guide vanes Ice Maximum Sucked in Maximum cruise To simulate a accumulation continuous on a typical maximum inlet cowl icing and engine encounter at face 25 deg.F. resulting from a 2- minute delay in actuating anti-icing system, or a slab of ice which is comparable in weight or thickness for that size engine Hail (0.8 to For all Rough air Maximum cruise In a volley 0.9 specific engines: With flight speed at 15,000 to simulate gravity) inlet area of of typical feet altitude a hailstone not more than aircraft encounter. 100 square One-half the inches: one number of 1-inch hailstones hailstone. aimed at With inlet random area area of more over the than 100 face of the square inlet and inches: one the other 1-inch and half aimed one 2-inch at the hailstone for critical each 150 face area. square inches of inlet area or fraction thereof For supersonic Supersonic Maximum cruise Aimed at engines (in cruise critical addition): 3 velocity. engine face hailstones Alternatively, area. each having a use subsonic diameter velocities equal to that with larger in a straight hailstones to line give variation equivalent from 1 inch kinetic energy at 35,000 feet to 1/4 inch at 60,000 feet using diameter corresponding to the lowest supersonic cruise altitude expected Water At least 4 Sucked in Flight idle, For 3 minutes percent of acceleration, each at idle engine takeoff, and takeoff, airflow by deceleration and during weight acceleration and deceleration in spray to simulate rain. Note.--The term "inlet area" as used in this section means the engine inlet projected area at the front face of the engine. It includes the projected area of any spinner or bullet nose that is provided. [Amdt. 33-10, 49 FR 6852, Feb. 23, 1984] Sec. 33.92 Windmilling tests. (a) For engines to be used in supersonic aircraft, unless means are incorporated in the engine to stop rotation of the engine rotors when the engine is shut down in flight, each engine rotor must either seize or be capable of rotation for 3 hours at the limiting windmilling rotational r.p.m. with no oil in the engine system, without the engine-- (1) Catching fire; (2) Bursting (releasing hazardous uncontained fragments); or (3) Generating loads greater than those ultimate loads specified in Sec. 33.23(a). (b) A turbojet or turbofan engine incorporating means to stop rotation of the engine rotors when the engine is shut down in flight must be subjected to 25 operations under the following conditions: (1) Each engine must be shut down while operating at rated maximum continuous thrust. (2) For engines certificated for use on supersonic aircraft, the temperature of the induction air and the external surfaces of the engine must be held at the maximum limit during the tests required by this paragraph. Sec. 33.94 Blade containment and rotor unbalance tests. (a) Except as provided in paragraph (b) of this section, it must be demonstrated by engine tests that the engine is capable of containing damage without catching fire and without failure of its mounting attachments when operated for at least 15 seconds, unless the resulting engine damage induces a self shutdown, after each of the following events: (1) Failure of the most critical compressor or fan blade while operating at maximum permissible r.p.m. The blade failure must occur at the outermost retention groove or, for integrally-bladed rotor discs, at least 80 percent of the blade must fail. (2) Failure of the most critical turbine blade while operating at maximum permissible r.p.m. The blade failure must occur at the outermost retention groove or, for integrally-bladed rotor discs, at least 80 percent of the blade must fail. The most critical turbine blade must be determined by considering turbine blade weight and the strength of the adjacent turbine case at case temperatures and pressures associated with operation at maximum permissible r.p.m. (b) Analysis based on rig testing, component testing, or service experience may be substitute for one of the engine tests prescribed in paragraphs (a)(1) and (a)(2) of this section if-- (1) That test, of the two prescribed, produces the least rotor unbalance; and (2) The analysis is shown to be equivalent to the test.