(a) The special factors prescribed in §§ 27.621 through 27.625 apply to each part of the structure whose strength is—

1. (1) Uncertain;
2. (2) Likely to deteriorate in service before normal replacement; or

3. (3) Subject to appreciable variability due to—

   1. (i) Uncertainties in manufacturing processes; or
   2. (ii) Uncertainties in inspection methods.

(b) For each part to which §§ 27.621 through 27.625 apply, the factor of safety prescribed in § 27.303 must be multiplied by a special factor equal to—

1. (1) The applicable special factors prescribed in §§ 27.621 through 27.625; or
2. (2) 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.