Downloaded from https://www.everyspec.com MIL-STD-1808C w/CHANGE 1 SYSTEM SUB-SYSTEM TITLE DEFINITION 05 50 FATIGUE INDEX CALCULATIONS The system procedures and formulas for calculating aircraft structural fatigue index and fatigue lives from fatigue meter readings. 60 OPERATING SPECTRUM(S) The system assumed operating spectrum(s) for the aircraft from which safe fatigue lives are calculated. 6