FAR25.521:General. ...................... 553 FAR 25.523 : Design weights and center of gravity positions. 554 FAR25.525:Applicationofloads. . . . . . . . . . . . . . . . 554 FAR 25.527 : Hull and main .oat load factors. . . . . . . . . 554 FAR 25.529 : Hull and main .oat landing conditions. . . . . 555 FAR 25.531 : Hull and main .oat takeo. conditions. . . . . . 555 FAR 25.533 : Hull and main .oat bottom pressures. . . . . . 556 FAR25.535:Auxiliary.oatloads. . . . . . . . . . . . . . . 557 FAR25.537:Seawingloads. .................. 559
46.8EmergencyLandingConditions . . . . . . . . . . . . . . . . . 559
FAR25.561:General. ...................... 559 FAR25.562:[Emergencylandingdynamicconditions.] . . . 560 FAR 25.563 : Structural ditching provisions. . . . . . . . . . 561
46.9FatigueEvaluation. . . . . . . . . . . . . . . . . . . . . . . . . 561
FAR25.571:Damage-tolerance andfatigue evaluation of struc-ture. .......................... 561 FAR25.573:[Reserved.] .................... 564
46.10LightningProtection ....................... 564

FAR25.581:[Lightningprotection.] . . . . . . . . . . . . . . 564
46.1 General
FAR 25.301 : Loads.
(a)
Strength requirements are speci.edin terms oflimitloads(the maximumloadsto be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety).Unless otherwiseprovided,prescribedloads arelimitloads.

(b)
Unless otherwiseprovided, the speci.ed air,ground, and waterloads mustbeplaced in equilibrium with inertia forces, considering each item of mass in the airplane. These loads must be distributed to conservatively approximate or closely represent actual conditions. [Methods used to determine load intensities and distribution must be validated by .ight load measurement unless the methods used for deter-mining those loading conditions are shown to be reliable.]

(c)
If de.ections under load would signi.cantly change the distribution of external or internal loads, this redistribution must be taken into account.

Amdt. 25-23, E.. 5/8/70
FAR 25.303 : Factor of safety.
[Unlessotherwisespeci.ed, afactor ofsafety of1.5 mustbe applied totheprescribed limitloadwhich are considered externalloads on the structure.When aloading condition is prescribed in terms of ultimate loads, a factor of safety need not be applied unless otherwise speci.ed.] Amdt. 25-23, E.. 5/8/70
FAR 25.305 : Strength and deformation.
(a)
The structure must be able to support limit loads without any detrimental perma-nent deformation. At any load up to limit loads the deformation may not interfere with safe operation.

(b)
The structure must be able to support ultimate loads without failure for at least 3 seconds. However, when proof of strength is shown by dynamic tests simulating actual load conditions, the 3-second limit does not apply. Static tests conducted to ultimate load must include the ultimate de.ections and ultimate deformation induced by the loading. When analytical methods are used to show compliance with the ultimate load strength requirements, it must be shown that–

(1)
The e.ects of deformation are not signi.cant;

(2)
The deformations involved are fully accounted for in the analysis; or

(3)
The methods and assumptions used are su.cient to cover the e.ects of these deformations.

(c)
Wherestructural.exibilityissuchthat any rateofload applicationlikely tooccurin the operating conditions might produce transient stresses appreciably higher than those corresponding to static loads, the e.ects of this rate of application must be considered.

(d)
[Reserved.]

(e)
The airplane must be designed to withstand any vibration and bu.eting that might occur in any likely operating condition up to VD/MD, including stall and pro-bable inadvertent excursions beyond the boundaries of the bu.et onset envelope.
　
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