(i)
The maximum disbonds of each bonded joint consistent with the capa-bility to withstand theloadsinparagraph(a)(3) ofthis section mustbe determined by analysis, tests, or both. Disbonds of each bonded joint greater than this must be prevented by design features; or

(ii)
Proof testing must be conducted on each production article that will apply the criticallimitdesignload to each criticalbondedjoint; or

(iii) Repeatable and reliable non-destructive inspection techniques must be established that ensurethe strength of eachjoint.

(6)
Structural components for which the damage tolerance method is shown to be impractical must be shown by component fatigue tests, or analysis supported by tests, to be able to withstand the repeated loads of variable magnitude expected in service. Su.cient component, subcomponent, element, or coupon tests mustbedoneto establishthefatigue scatterfactor andthe environmental e.ects.Damage up to the threshold ofdetectability and ultimateload residual strength capability must be considered in the demonstration.

(b) Metallic airframe structure. If the applicant elects to use Sec. 23.571[(a)(3)] or Sec. 23.572(a)(3),then thedamage tolerance evaluation mustinclude adetermination of theprobablelocations and modes ofdamagedue tofatigue, 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 fatigue must be included where the design is such that this type of damage can be expected to occur.The evaluation mustincorporate repeatedload and static analyses supported by test evidence. The extent of damage for residual strength evaluation at any time within the operational life of the airplane 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 critical limit .ight loads, considered as ultimate, with the extent of detectable damage consistent with the results of the damage tolerance evaluations. For pressurized cabins, the following load must be withstood :]
(1)
The normal operating di.erential pressure combined with the expected ex-ternal aerodynamic pressures applied simultaneously with the .ight loading conditions speci.ed in this part, and

(2)
The expected external aerodynamic pressures in 1g .ight combined with a cabindi.erentialpressureequal to1.1 timesthe normal operating di.erential pressure without any other load.

(c) [[Removed.]] Amdt. 23-48, E.. 03/11/96
FAR23.574 :[Metallicdamagetolerance andfatigue evaluation of commuter category airplanes.]
[For commuter categoryairplanes–
(a)
Metallic damage tolerance. An evaluation of the strength, detail design, and fabri-cation must show that catastrophic failure due to fatigue, corrosion, defects, or damage will be avoided throughout the operational life of the airplane. This eva-luationmustbe conductedin accordancewith theprovisionsofSec.23.573,except as speci.ed in paragraph (b) of this section, for each part of the structure that could contribute to a catastrophic failure.

(b)
Fatigue(safe-life) evaluation. Compliance with the damage tolerance requirements of paragraph (a) of this section is not required if the applicant establishes that the applicationof thoserequirementsisimpracticalforaparticularstructure.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.]

Amdt. 23-48, E.. 03/11/96
FAR23.575 :[Inspections and otherprocedures.]
[Eachinspection or otherprocedure,basedon an evaluation requiredby Secs.23.571, 23.572, 23.573 or 23.574, must be established to prevent catastrophic failure and must be included in the Limitations Section of the Instructions for Continued Airworthiness required by Sec. 23.1529.] Amdt. 23-48, E.. 03/11/96
　
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