Engine Separation During Climb on USAir Flight 224 (N319AU)

Incident Description

During takeoff, as USAir Flight 224 was climbing through 4000 feet, the aircraft yawed and rolled to the right. Simultaneously, the crew observed the number 2 throttle slam and lock to the idle position, and a continuous airframe buffet began. Shortly thereafter, the number 2 engine separated from the aircraft and the buffet stopped. The engine impacted in an open field 6 miles from the airport. Just before the separation, a passenger reported seeing the aft end of the number 2 engine momentarily droop by about 30 degrees. After the engine separated, the 'B' hydraulic system lost pressure and the trailing edge flaps would only extend to 10 degrees. The aircraft was landed safely after an emergency gear extension; differential braking was used for steering.

Examination Findings

An examination revealed that the aft mount cone bolt for the number 2 engine had failed from fatigue through the thread relief undercut radius. Fatigue cracks had initiated on diametrically opposite sides of the radius. Subsequently, the forward mount cone bolts and secondary support cable failed from overload.