Raytheon Aircraft Company 400A N193BJ incident near Rochester, New York

Probable cause

The probable cause of the uncontained No. 2 engine failure on the Raytheon Beechjet 400A was a herring gull birdstrike that resulted in fan blade contact with the inlet case and rub induced excitation of a previously unidentified natural frequency (resonance) within the engine operating range.

NTSB analysis

The No. 2 engine sustained a herring gull bird strike during takeoff climb from Rochester International Airport- Rochester, NY. The impact from the birdstrike resulted in contact between the fan and inlet case that separated eleven (11) of the nineteen (19) fan blades and subsequently led to the failure of the No. 1 bearing housing, and a midshaft fracture of the low pressure turbine shaft. Materials analysis on recovered fan blade fragments determined that all separated blades failed due to overload and no evidence of fatigue was identified. A series of modal tests including: tap hammer, high energy shaker, and computer model simulation were conducted at the system and component level. The tests identified a four nodal diameter coincidence at about 72% N1 speed. When sufficient energy is imparted to the engine fan during a foreign object ingestion event like a birdstrike, it may result in a rub induced excitation and subsequent fan blade separation and catastrophic engine failure.

Text from the NTSB. Open the NTSB docket for ENG14IA011 for the full record.