Federal Aviation Administration, DOT § 23.729

nj=the load factor developed in the drop test torque, and air loads, occurring during (that is, the acceleration (dv/dt) in gs re- retraction at any airspeed up to 1.6 VS1 corded in the drop test) plus 1.0; and with flaps retracted, and for any load We, W, and L are the same as in the drop test factor up to those specified in § 23.345 computation. for the flaps-extended condition. (f) The value of n determined in ac- (2) The landing gear and retracting cordance with paragraph (e) may not mechanism, including the wheel well be more than the limit inertia load fac- doors, must withstand flight loads, in- tor used in the landing conditions in cluding loads resulting from all yawing § 23.473. conditions specified in § 23.351, with the [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as landing gear extended at any speed up amended by Amdt. 23–7, 34 FR 13091, Aug. 13, to at least 1.6 VS1 with the flaps re- 1969; Amdt. 23–48, 61 FR 5148, Feb. 9, 1996] tracted. (b) Landing gear lock. There must be § 23.726 Ground load dynamic tests. positive means (other than the use of (a) If compliance with the ground hydraulic pressure) to keep the landing load requirements of §§ 23.479 through gear extended. 23.483 is shown dynamically by drop (c) Emergency operation. For a land- test, one drop test must be conducted plane having retractable landing gear that meets § 23.725 except that the drop that cannot be extended manually, height must be— there must be means to extend the (1) 2.25 times the drop height pre- landing gear in the event of either— scribed in § 23.725(a); or (1) Any reasonably probable failure in (2) Sufficient to develop 1.5 times the the normal landing gear operation sys- limit load factor. tem; or (b) The critical landing condition for (2) Any reasonably probable failure in each of the design conditions specified a power source that would prevent the in §§ 23.479 through 23.483 must be used operation of the normal landing gear for proof of strength. operation system. [Amdt. 23–7, 34 FR 13091, Aug. 13, 1969] (d) Operation test. The proper func- tioning of the retracting mechanism § 23.727 Reserve energy absorption must be shown by operation tests. drop test. (e) Position indicator. If a retractable (a) If compliance with the reserve en- landing gear is used, there must be a ergy absorption requirement in landing gear position indicator (as well § 23.723(b) is shown by free drop tests, as necessary switches to actuate the the drop height may not be less than indicator) or other means to inform the 1.44 times that specified in § 23.725. pilot that each gear is secured in the (b) If the effect of wing lift is pro- extended (or retracted) position. If vided for, the units must be dropped switches are used, they must be located with an effective mass equal to We=Wh/ and coupled to the landing gear me- (h+d), when the symbols and other de- chanical system in a manner that pre- tails are the same as in § 23.725. vents an erroneous indication of either [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as ‘‘down and locked’’ if each gear is not amended by Amdt. 23–7, 34 FR 13091, Aug. 13, in the fully extended position, or ‘‘up 1969] and locked’’ if each landing gear is not in the fully retracted position. § 23.729 Landing gear extension and (f) Landing gear warning. For land- retraction system. planes, the following aural or equally (a) General. For airplanes with re- effective landing gear warning devices tractable landing gear, the following must be provided: apply: (1) A device that functions continu- (1) Each landing gear retracting ously when one or more throttles are mechanism and its supporting struc- closed beyond the power settings nor- ture must be designed for maximum mally used for landing approach if the flight load factors with the gear re- landing gear is not fully extended and tracted and must be designed for the locked. A throttle stop may not be combination of friction, inertia, brake used in place of an aural device. If

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there is a manual shutoff for the warn- (1) By a load on each main wheel tire) ing device prescribed in this paragraph, to be compared to the static rating ap- the warning system must be designed proved for such tires) equal to the cor- so that when the warning has been sus- responding static ground reaction pended after one or more throttles are under the design maximum weight and closed, subsequent retardation of any critical center of gravity; and throttle to, or beyond, the position for (2) By a load on nose wheel tires (to normal landing approach will activate be compared with the dynamic rating the warning device. approved for such tires) equal to the re- (2) A device that functions continu- action obtained at the nose wheel, as- ously when the wing flaps are extended suming the mass of the airplane to be beyond the maximum approach flap po- concentrated at the most critical cen- sition, using a normal landing proce- ter of gravity and exerting a force of dure, if the landing gear is not fully ex- 1.0 W downward and 0.31 W forward tended and locked. There may not be a (where W is the design maximum manual shutoff for this warning device. weight), with the reactions distributed The flap position sensing unit may be to the nose and main wheels by the installed at any suitable location. The principles of statics and with the drag system for this device may use any reaction at the ground applied only at part of the system (including the aural wheels with brakes. warning device) for the device required (b) If specially constructed tires are in paragraph (f)(1) of this section. used, the wheels must be plainly and (g) Equipment located in the landing conspicuously marked to that effect. gear bay. If the landing gear bay is used The markings must include the make, as the location for equipment other size, number of plies, and identification than the landing gear, that equipment marking of the proper tire. must be designed and installed to mini- (c) Each tire installed on a retract- mize damage from items such as a tire able landing gear system must, at the burst, or rocks, water, and slush that maximum size of the tire type expected may enter the landing gear bay. in service, have a clearance to sur- rounding structure and systems that is [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as amended by Amdt. 23–7, 34 FR 13091, Aug. 13, adequate to prevent contact between 1969; Amdt. 23–21, 43 FR 2318, Jan. 1978; Amdt. the tire and any part of the structure 23–26, 45 FR 60171, Sept. 11, 1980; Amdt. 23–45, of systems. 58 FR 42164, Aug. 6, 1993; Amdt. 23–49, 61 FR [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as 5166, Feb. 9, 1996] amended by Amdt. 23–7, 34 FR 13092, Aug. 13, 1969; Amdt. 23–17, 41 FR 55464, Dec. 20, 1976; § 23.731 Wheels. Amdt. 23–45, 58 FR 42165, Aug. 6, 1993] (a) The maximum static load rating of each wheel may not be less than the § 23.735 Brakes. corresponding static ground reaction (a) Brakes must be provided. The with— landing brake kinetic energy capacity (1) Design maximum weight; and rating of each main wheel brake assem- (2) Critical center of gravity. bly must not be less than the kinetic (b) The maximum limit load rating of energy absorption requirements deter- each wheel must equal or exceed the mined under either of the following maximum radial limit load determined methods: under the applicable ground load re- (1) The brake kinetic energy absorp- quirements of this part. tion requirements must be based on a conservative rational analysis of the [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as amended by Amdt. 23–45, 58 FR 42165, Aug. 6, sequence of events expected during 1993] landing at the design landing weight. (2) Instead of a rational analysis, the § 23.733 Tires. kinetic energy absorption require- ments for each main wheel brake as- (a) Each landing gear wheel must sembly may be derived from the fol- have a tire whose approved tire ratings lowing formula: (static and dynamic) are not exceed- ed— KE=0.0443 WV2/N

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