A method of developing the design flight-by-flight sequenced stress spectrum at any location within the primary airframe structure is presented.

The procedure commences with the applicable procurement specifications for the aircraft and concludes with the detail's local stress spectrum suitable for fatigue and fracture mechanics analyses or testing. The stress spectrum is created within a computer program that utilizes input data comprising mission profiles, structural location data, libraries of load factor exceedance data, balanced external load conditions, and corresponding internal loads solutions. The output consists of the spectrum in tabular form and the time trace graphs of the stress amplitude.

Included is a typical spectrum developed for a variable geometry bomber with terrain-following capability, and discussion as to load sequence effects and the structural internal loads solutions necessary to describe the stress trace on a mission-by-mission basis.

Finally, the system-generated spectrum is discussed in terms of its effect on fatigue and fracture mechanics analysis.