FAA Federal Aviation Regulations (FARS, 14 CFR)

A fatigue evalution must be made and the fatigue limits determined for each metallic hub and blade, and each primary load carrying metal component of nonmetallic blades. The fatigue evaluation must include consideration of all reasonably foreseeable vibration load patterns. The fatigue limits must account for the permissible service deteriortion (such as nicks, grooves, galling, bearing wear, and variations in material properties).

[Amdt. 35-5, 45 FR 60182, Sept. 11, 1980]