SAFE OPERATION OF A FLEET OF AIRCRAFT LIKELY TO CONTAIN GROWING FATIGUE CRACKS.

Technological advances and operational pressures have encouraged the operation of aircraft structures with either suspected or known cracks. Airworthiness requirements for military aircraft have evolved to the point where 'fail-safe' and 'damage-tolerance' philosophies, which assume the existence of a crack and rely on in-service inspections to maintain safety, are being applied to both new designs and existing fleets. These applications depend on models for predicting crack growth rates hence inspection intervals in service. This paper reviews airworthiness requirements, crack growth models, and other issues relevant to the estimation of inspection intervals.