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Federal Aviation Administration, DOT § 25.965

(C) Cowl flaps (or other means of con- ments, low energy debris, or trolling the engine cooling supply) in other likely debris. the position that provides adequate (2) All covers must be fire resistant cooling in the hot-day condition. as defined in part 1 of this chapter. (D) Engine operating within the max- (f) For pressurized tanks, a imum continuous power limitations. means with fail-safe features must be (E) Maximum takeoff weight; and provided to prevent the buildup of an (ii) For turbine engine powered air- excessive pressure difference between planes, the maximum airspeed estab- the inside and the outside of the tank. lished for climbing from takeoff to the [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as maximum operating altitude. amended by Amdt. 25–40, 42 FR 15043, Mar. 17, (5) The fuel temperature must be at 1977; Amdt. 25–69, 54 FR 40354, Sept. 29, 1989] least 110 °F. (b) The test prescribed in paragraph § 25.965 Fuel tank tests. (a) of this section may be performed in (a) It must be shown by tests that the flight or on the ground under closely fuel tanks, as mounted in the airplane, simulated flight conditions. If a flight can withstand, without failure or leak- test is performed in weather cold age, the more critical of the pressures enough to interfere with the proper resulting from the conditions specified conduct of the test, the fuel tank sur- in paragraphs (a)(1) and (2) of this sec- faces, fuel lines, and other fuel system tion. In addition, it must be shown by parts subject to cold air must be insu- either analysis or tests, that tank sur- lated to simulate, insofar as prac- faces subjected to more critical pres- ticable, flight in hot weather. sures resulting from the condition of [Amdt. 25–11, 32 FR 6912, May 5, 1967, as paragraphs (a)(3) and (4) of this section, amended by Amdt. 25–57, 49 FR 6848, Feb. 23, are able to withstand the following 1984] pressures: (1) An internal pressure of 3.5 psi. § 25.963 Fuel tanks: general. (2) 125 percent of the maximum air (a) Each fuel tank must be able to pressure developed in the tank from withstand, without failure, the vibra- ram effect. tion, inertia, fluid, and structural loads (3) Fluid pressures developed during that it may be subjected to in oper- maximum limit accelerations, and de- ation. flections, of the airplane with a full (b) Flexible fuel tank liners must be tank. approved or must be shown to be suit- (4) Fluid pressures developed during able for the particular application. the most adverse combination of air- (c) Integral fuel tanks must have fa- plane roll and fuel load. cilities for interior inspection and re- (b) Each metallic tank with large un- pair. supported or unstiffened flat surfaces, (d) Fuel tanks within the whose failure or deformation could contour must be able to resist rupture cause fuel leakage, must be able to and to retain fuel, under the inertia withstand the following test, or its forces prescribed for the emergency equivalent, without leakage or exces- landing conditions in § 25.561. In addi- sive deformation of the tank walls: tion, these tanks must be in a pro- (1) Each complete tank assembly and tected position so that exposure of the its supports must be vibration tested tanks to scraping action with the while mounted to simulate the actual ground is unlikely. installation. (e) Fuel tank access covers must (2) Except as specified in paragraph comply with the following criteria in (b)(4) of this section, the tank assembly order to avoid loss of hazardous quan- must be vibrated for 25 hours at an am- tities of fuel: plitude of not less than 1⁄32 of an inch (1) All covers located in an area (unless another amplitude is substan- where experience or analysis indicates tiated) while 2⁄3 filled with water or a strike is likely must be shown by other suitable test fluid. analysis or tests to minimize penetra- (3) The test frequency of vibration tion and deformation by tire frag- must be as follows:

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(i) If no frequency of vibration result- (1) There must be pads, if necessary, ing from any r.p.m. within the normal to prevent chafing between the tank operating range of engine speeds is and its supports; critical, the test frequency of vibration (2) Padding must be nonabsorbent or must be 2,000 cycles per minute. treated to prevent the absorption of (ii) If only one frequency of vibration fluids; resulting from any r.p.m. within the (3) If a flexible tank liner is used, it normal operating range of engine must be supported so that it is not re- speeds is critical, that frequency of vi- quired to withstand fluid loads; and bration must be the test frequency. (4) Each interior surface of the tank compartment must be smooth and free (iii) If more than one frequency of vi- of projections that could cause wear of bration resulting from any r.p.m. with- the liner unless— in the normal operating range of en- (i) Provisions are made for protection gine speeds is critical, the most crit- of the liner at these points; or ical of these frequencies must be the (ii) The construction of the liner test frequency. itself provides that protection. (4) Under paragraphs (b)(3)(ii) and (b) Spaces adjacent to tank surfaces (iii) of this section, the time of test must be ventilated to avoid fume accu- must be adjusted to accomplish the mulation due to minor leakage. If the same number of vibration cycles that tank is in a sealed compartment, ven- would be accomplished in 25 hours at tilation may be limited to drain holes the frequency specified in paragraph large enough to prevent excessive pres- (b)(3)(i) of this section. sure resulting from altitude changes. (5) During the test, the tank assem- (c) The location of each tank must bly must be rocked at the rate of 16 to meet the requirements of § 25.1185(a). 20 complete cycles per minute, through (d) No engine skin imme- an angle of 15° on both sides of the hor- diately behind a major air outlet from izontal (30° total), about the most crit- the engine compartment may act as ical axis, for 25 hours. If motion about the wall of an integral tank. more than one axis is likely to be crit- (e) Each fuel tank must be isolated ical, the tank must be rocked about from personnel compartments by a fumeproof and fuelproof enclosure. each critical axis for 121⁄2 hours. (c) Except where satisfactory oper- § 25.969 Fuel tank expansion space. ating experience with a similar tank in Each fuel tank must have an expan- a similar installation is shown, non- sion space of not less than 2 percent of metallic tanks must withstand the test the tank capacity. It must be impos- specified in paragraph (b)(5) of this sec- sible to fill the expansion space inad- tion, with fuel at a temperature of 110 vertently with the airplane in the nor- ° F. During this test, a representative mal ground attitude. For pressure fuel- specimen of the tank must be installed ing systems, compliance with this sec- in a supporting structure simulating tion may be shown with the means pro- the installation in the airplane. vided to comply with § 25.979(b). (d) For pressurized fuel tanks, it must be shown by analysis or tests [Amdt. 25–11, 32 FR 6913, May 5, 1967] that the fuel tanks can withstand the § 25.971 Fuel tank . maximum pressure likely to occur on the ground or in flight. (a) Each fuel tank must have a sump with an effective capacity, in the nor- [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as mal ground attitude, of not less than amended by Amdt. 25–11, 32 FR 6913, May 5, the greater of 0.10 percent of the tank 1967; Amdt. 25–40, 42 FR 15043, Mar. 17, 1977] capacity or one-sixteenth of a gallon unless operating limitations are estab- § 25.967 Fuel tank installations. lished to ensure that the accumulation (a) Each fuel tank must be supported of water in service will not exceed the so that tank loads (resulting from the sump capacity. weight of the fuel in the tanks) are not (b) Each fuel tank must allow drain- concentrated on unsupported tank sur- age of any hazardous quantity of water faces. In addition— from any part of the tank to its sump

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