(4)
The lap safety belt must remain on the occupant’s pelvis during the impact.

(5)
Eachoccupant mustbeprotectedfrom seriousheadinjury underthe conditions prescribedinparagraph(b) of this section.Wherehead contact with seats or other structure can occur,protection mustbeprovided sothattheheadimpact does notexceed aHeadInjuryCriterion(HIC) of1,000 units.Thelevel ofHIC is de.ned by the equation :

4 2.5
t2
1
HIC =(t2 .t1) a(t)dt
(t2 .t1) t1
max
Where :
t1 : is the initial integration time, t2 : is the .nal integration time, and a(t): is the total acceleration vs. time curve for the head strike, and where
(t)
: is in seconds, and

(a)
:isinunitsofgravity(g).

(6)
Whereleg injuries may resultfrom contact with seats or other structure,pro-tection must beprovided toprevent axially compressiveloads exceeding 2,250 pounds in each femur.

(7)
The seatmust remain attached at allpoints of attachment, although the struc-ture may haveyielded.

(8)
Seats mustnotyield underthe tests speci.edinparagraphs(b)(1) and(b)(2) of this section to the extent they would impede rapid evacuation of the airplane occupants.]

Amdt. 25-64, E.. 6/16/88
FAR 25.563 : Structural ditching provisions.
Structural strength considerations ofditchingprovisions mustbein accordance with Sec. 25.801(e).
46.9 Fatigue Evaluation
FAR 25.571 : Damage-tolerance and fatigue evaluation of structure.
(a) [General. An evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to fatigue, corrosion, manufacturing defects, or acci-dentaldamage, willbe avoidedthroughout the operationallife of the airplane.This evaluation mustbe conductedin accordance with theprovisions ofparagraphs(b)
′
Elodie Roux. Septembre 2003
Subpart C : Structure
and(e) of this section, except as speci.edinparagraph(c) of this section,for each part of the structurethat could contributeto a catastrophicfailure(such as wing, empennage, control surfaces and their systems, the fuselage, engine mounting, lan-dinggear, and their relatedprimary attachments). For turbojetpowered airplanes, those parts that could contribute to a catastrophic failure must also be evaluated underparagraph(d) of this section.In addition,thefollowing apply :]
(1)
Each evaluation required by this section must include–

(i)
The typical loading spectra, temperatures, and humidities expected in service;

(ii)
Theidenti.cation ofprincipalstructural elements anddetaildesignpoints, the failure of which could cause catastrophic failure of the airplane; and

(iii) An analysis, supported by test evidence, of the principal structural ele-ments anddetaildesignpointsidenti.edinparagraph(a)(1)(ii) ofthis section.

(2)
The servicehistoryof airplanes of similar structuraldesign, takingdue account of di.erences in operating conditions and procedures, may be used in the evaluations required by this section.

(3)
[Basedonthe evaluations requiredby this section,inspections or otherproce-dures must be established, as necessary, to prevent catastrophic failure, and must be included in the Airworthiness Limitations Section of the Instructions for Continued Airworthiness required by Sec. 25.1529. Inspection thresholds for the following types of structure mustbe establishedbased on crackgrowth analyses and/or tests, assuming the structure contains an initial .aw of the maximumprobable sizethat could exist as a result of manufacturing or service-induced damage :

(i)
Single load path structure, and

(ii)
Multipleloadpath ”fail-safe”structureand crack arrest ”fail-safe”struc-ture, where it cannot be demonstrated that load path failure, partial fai-lure, or crack arrest will be detected and repaired during normal main-tenance, inspection, or operation of an airplane prior to failure of the remaining structure.]
　
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