14 CFR § 23.2265

The applicant must determine a special factor of safety for each critical design value for each part, article, or assembly for which that critical design value is uncertain, and for each part, article, or assembly that is—

Likely to deteriorate in service before normal replacement; or

Subject to appreciable variability because of uncertainties in manufacturing processes or inspection methods.

The applicant must determine a special factor of safety using quality controls and specifications that account for each—

Type of application;

Inspection method;

Structural test requirement;

Sampling percentage; and

Process and material control.

The applicant must multiply the highest pertinent special factor of safety in the design for each part of the structure by each limit and ultimate load, or ultimate load only, if there is no corresponding limit load, such as occurs with emergency condition loading.