For the past thirty-five years the United States Air Force used the USAF Aircraft Structural Integrity Program (ASIP) to maintain safe and economical operation of aging aircraft. That program has been supported over the years by Air Force laboratory programs in the areas of fracture mechanics, corrosion prevention, flight loads, nondestructive evaluation, human factors, and maintenance and repair. These efforts provided the Air Force with the technology required to support the operational aircraft maintenance programs based on damage tolerance. There has also been a mutual need to develop the capability to estimate the time of onset of widespread fatigue damage that could degrade the damage tolerance capability of aircraft. It is the purpose of this paper to discuss the USAF aging aircraft program and its associated efforts.