Review of airframe inspection interval for transport airplanes based on damage tolerance analysis

Abstract

Monitoring the life and managing the airworthiness of the airframes (aircraft structures) is an activity to maintain the aircraft structural integrity, which is part of the Aircraft Structural Integrity Program (ASIP). Airframes of modern transport airplanes are designed based on the Damage Tolerance Analysis (DTA). DTA concept assumes that damages in the form of cracks already exist in structures. In DTA designed structures, inspection is critical in ensuring the safety and integrity. DTAis based on the design spectrum load defined by the Original Equipment Manufacturer (OEM). As the actual operation might result in load spectrum which is different than the OEM design load spectrum, ASIP requires the actual stress spectra monitoring. Inspection review needs to be conducted using DTA, based on the actual stress spectra. The crack propagation scenario needs to be analysed. The time required for a crack to reach its critical length needs to be predicted. This will determine the inspection scenario. This paper introduces the DTA based airframe inspection review, and discusses the methodology to do it.