14 CFR § 29.619

The special factors prescribed in §§ 29.621 through 29.625 apply to each part of the structure whose strength is—

Uncertain;

Likely to deteriorate in service before normal replacement; or

Subject to appreciable variability due to—

Uncertainties in manufacturing processes; or

Uncertainties in inspection methods.

For each part of the rotorcraft to which §§ 29.621 through 29.625 apply, the factor of safety prescribed in § 29.303 must be multiplied by a special factor equal to—

The applicable special factors prescribed in §§ 29.621 through 29.625; or

Any other factor great enough to ensure that the probability of the part being understrength because of the uncertainties specified in paragraph (a) of this section is extremely remote.