Federal Aviation Administration, DOT § 23.965

that it may be subjected to in oper- (1) Each complete tank assembly and ation. its support must be vibration tested (b) Each flexible tank liner must while mounted to simulate the actual be shown to be suitable for the par- installation. ticular application. (2) Except as specified in paragraph (c) Each integral fuel tank must have (b)(4) of this section, the tank assembly adequate facilities for interior inspec- must be vibrated for 25 hours at a total tion and repair. displacement of not less than 1⁄32 of an (d) The total usable capacity of the inch (unless another displacement is fuel tanks must be enough for at least substantiated) while 2⁄3 filled with one-half hour of operation at maximum water or other suitable test fluid. continuous power. (3) The test frequency of vibration (e) Each fuel quantity indicator must must be as follows: be adjusted, as specified in § 23.1337(b), (i) If no frequency of vibration result- to account for the unusable fuel supply ing from any rpm within the normal determined under § 23.959(a). operating range of or propeller [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964; 30 speeds is critical, the test frequency of FR 258, Jan. 9, 1965, as amended by Amdt 23– vibration is: 34, 52 FR 1832, Jan. 15, 1987; Amdt. 23–43, 58 (A) The number of cycles per minute FR 18972, Apr. 9, 1993; Amdt. 23–51, 61 FR 5136, obtained by multiplying the maximum Feb. 9, 1996] continuous propeller speed in rpm by § 23.965 Fuel tank tests. 0.9 for propeller-driven airplanes, and (B) For non-propeller driven air- (a) Each fuel tank must be able to planes the test frequency of vibration withstand the following pressures with- is 2,000 cycles per minute. out failure or leakage: (1) For each conventional metal tank (ii) If only one frequency of vibration and nonmetallic tank with walls not resulting from any rpm within the nor- supported by the airplane structure, a mal operating range of engine or pro- pressure of 3.5 p.s.i., or that pressure peller speeds is critical, that frequency developed during maximum ultimate of vibration must be the test fre- acceleration with a full tank, which- quency. ever is greater. (iii) If more than one frequency of vi- (2) For each integral tank, the pres- bration resulting from any rpm within sure developed during the maximum the normal operating range of engine limit acceleration of the airplane with or propeller speeds is critical, the most a full tank, with simultaneous applica- critical of these frequencies must be tion of the critical limit structural the test frequency. loads. (4) Under paragraph (b)(3) (ii) and (iii) (3) For each nonmetallic tank with of this section, the time of test must be walls supported by the airplane struc- adjusted to accomplish the same num- ture and constructed in an acceptable ber of vibration cycles that would be manner using acceptable basic tank accomplished in 25 hours at the fre- material, and with actual or simulated quency specified in paragraph (b)(3)(i) support conditions, a pressure of 2 p.s.i. of this section. for the first tank of a specific design. (5) During the test, the tank assem- The supporting structure must be de- bly must be rocked at a rate of 16 to 20 signed for the critical loads occurring complete cycles per minute, through in the flight or landing strength condi- an angle of 15° on either side of the hor- tions combined with the fuel pressure izontal (30° total), about an axis par- loads resulting from the corresponding allel to the axis of the , for 25 accelerations. hours. (b) Each fuel tank with large, unsup- (c) Each integral tank using methods ported, or unstiffened flat sur- of construction and sealing not pre- faces,whose failure or deformation viously proven to be adequate by test could cause fuel leakage, must be able data or service experience must be able to withstand the following test without to withstand the vibration test speci- leakage, failure, or excessive deforma- fied in paragraphs (b)(1) through (4) of tion of the tank walls: this section.

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(d) Each tank with a nonmetallic lies immediately behind a major air liner must be subjected to the sloshing opening from the engine compartment test outlined in paragraph (b)(5) of this may act as the wall of an integral section, with the fuel at room tempera- tank. ture. In addition, a specimen liner of (d) Each fuel tank must be isolated the same basic construction as that to from personnel compartments by a be used in the airplane must, when in- fume-proof and fuel-proof enclosure stalled in a suitable test tank, with- that is vented and drained to the exte- stand the sloshing test with fuel at a rior of the airplane. The required en- ° temperature of 110 F. closure must sustain any personnel [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as compartment pressurization loads amended by Amdt. 23–43, 58 FR 18972, Apr. 9, without permanent deformation or fail- 1993; Amdt. 23–43, 61 FR 253, Jan. 4, 1996; ure under the conditions of §§ 23.365 and Amdt. 23–51, 61 FR 5136, Feb. 9, 1996] 23.843 of this part. A bladder-type fuel § 23.967 Fuel tank installation. cell, if used, must have a retaining shell at least equivalent to a metal fuel (a) Each fuel tank must be supported so that tank loads are not con- tank in structural integrity. centrated. In addition— (e) Fuel tanks must be designed, lo- (1) There must be pads, if necessary, cated, and installed so as to retain fuel: to prevent chafing between each tank (1) When subjected to the inertia and its supports; loads resulting from the ultimate stat- (2) Padding must be nonabsorbent or ic load factors prescribed in treated to prevent the absorption of § 23.561(b)(2) of this part; and fuel; (2) Under conditions likely to occur (3) If a flexible tank liner is used, it when the airplane lands on a paved must be supported so that it is not re- runway at a normal landing speed quired to withstand fluid loads; under each of the following conditions: (4) Interior surfaces adjacent to the (i) The airplane in a normal landing liner must be smooth and free from attitude and its retracted. projections that could cause wear, un- (ii) The most critical landing gear leg less— collapsed and the other landing gear (i) Provisions are made for protection of the liner at those points; or legs extended. (ii) The construction of the liner In showing compliance with paragraph itself provides such protection; and (e)(2) of this section, the tearing away (5) A positive pressure must be main- of an engine mount must be considered tained within the vapor space of each unless all the are installed bladder cell under any condition of op- above the wing or on the tail or fuse- eration, except for a particular condi- lage of the airplane. tion for which it is shown that a zero or negative pressure will not cause the [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as amended by Amdt. 23–7, 34 FR 13903, Aug. 13, bladder cell to collapse; and 1969; Amdt. 23–14, 38 FR 31823, Nov. 19, 1973; (6) Syphoning of fuel (other than Amdt. 23–18, 42 FR 15041, Mar. 17, 1977; Amdt. minor spillage) or collapse of bladder 23–26, 45 FR 60171, Sept. 11, 1980; Amdt. 23–36, fuel cells may not result from improper 53 FR 30815, Aug. 15, 1988; Amdt. 23–43, 58 FR securing or loss of the fuel filler cap. 18972, Apr. 9, 1993] (b) Each tank compartment must be ventilated and drained to prevent the § 23.969 Fuel tank expansion space. accumulation of flammable fluids or Each fuel tank must have an expan- vapors. Each compartment adjacent to sion space of not less than two percent a tank that is an integral part of the airplane structure must also be venti- of the tank capacity, unless the tank lated and drained. vent discharges clear of the airplane (c) No fuel tank may be on the engine (in which case no expansion space is re- side of the firewall. There must be at quired). It must be impossible to fill least one-half inch of clearance be- the expansion space inadvertently with tween the fuel tank and the firewall. the airplane in the normal ground atti- No part of the engine skin that tude.

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