Raytheon Aircraft Company 400A N412GJ incident near Sugar Land, Texas

Probable cause

The probable cause of the uncontained No. 2 engine failure on the Raytheon Beechjet 400A was a yellow-crowned night-heron 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 yellow-crowned night-heron birdstrike during takeoff roll from Sugar Land Regional Airport (SGR)- Sugar Land, Texas. The impact from the birdstrike resulted in contact between the fan and inlet case that separated all nineteen (19) fan blades. The released blade fragments penetrated the engine case and cowl and caused an engine fire. A blade fragment impacted the right wing and punctured the fuel tank resulting in fuel spillage onto the wing surface and runway. 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 ENG14IA013 for the full record.