Analysis of an In-Flight Flap Actuation Jackscrew Bearing Failure

During a flight, the inboard flap of a B-52 tore apart and separated, initiating an in-flight emergency. After recovery of the flap segment and investigation of several structural and non-structural components, a jackscrew bearing was discovered to have failed, causing the actuation mechanism to decouple and the flap to tear apart. Further analysis identified the 52100 steel inner race ring of the aerospace-grade bearing to be non-uniformly heat treated and therefore not properly hardened to design requirements. This caused the inner ring of the bearing to deform and wear away. This degree of freedom allowed the jackscrew to axially shift and decouple from the gearbox. Metallography and hardness mapping exhibited wide microstructural variations and softened regions in the bearing ring. Other bearings identified on the aircraft from the same manufacturing lot exhibited similar mechanical property discrepancies. Bearings of this lot were identified and removed from the supply chain, and further hardness testing was conducted on additional lots to verify compliance. This investigation highlighted the importance of manufacturing and supply chain quality controls.