In engineering, damage tolerance is a property of a structure relating to its ability to sustain defects safely until repair can be effected.
"[1] Prior to the 1970s, the prevailing engineering philosophy of aircraft structures was to ensure that airworthiness was maintained with a single part broken, a redundancy requirement known as fail-safety.
However, advances in fracture mechanics, along with infamous catastrophic fatigue failures such as those in the de Havilland Comet prompted a change in requirements for aircraft.
Due to the extremely large numbers of cycles endured by the rotating component, an undetectable crack may grow to a critical length in a single flight and before the aircraft lands, result in a catastrophic failure that regular maintenance could not have prevented.
Manufacturers and operators of aircraft, trains, and civil engineering structures like bridges have a financial interest in ensuring that the inspection schedule is as cost-efficient as possible.