Evaluation of a PC-9/A Wing Main Spar with Misdrills Using Enhanced Teardown at Resonance

Widespread production misdrills in Royal Australian Air Force (RAAF) PC-9/A wing main spar lower caps were a potential threat to airworthiness and fleet availability late in the service life of the aircraft. A rapid, novel, enhanced teardown of a retired RAAF PC-9/A wing spar with production misdrills was successfully completed to address this risk. Dynamic block loading was applied to the main spar lower cap of a wing with multiple misdrill indications identified in-service using x-ray inspection. Using an enhanced teardown experimental method and cycling the wing at resonance, fatigue failure occurred within the test section from a main spar misdrill in less than fifty cumulative hours of cycling. A damage tolerance prediction, testing results, teardown inspection and forensic assessment of the spar lower cap was combined to deliver timely and valuable risk mitigation advice for PC-9/A fleet structural integrity managers. Greater confidence in existing fleet management was fostered in a very short timeframe and the opportunity presented by a retired wing with misdrills was fully leveraged. In addition, an innovative structural experimentation method for aircraft sustainment was pioneered.