Incident Overview
On March 13, 2014, at about 1020 eastern daylight time, a Raytheon Beechjet 400A, registration N193BJ, experienced a No. 2 (right) engine bird strike shortly after takeoff from Greater Rochester International Airport (ROC), Rochester, New York. The aircraft was equipped with two Pratt & Whitney Canada JT15D-5 engines. The crew declared an emergency, returned to the airport, and made an uneventful landing at ROC.
Damage Assessment
During an inspection, extensive damage to the No. 2 engine fan and inlet cowl was observed. The compressor cowl had multiple holes and the right wing had an impact mark forward of the engine inlet case. The No. 2 engine core cowl upper inboard and outboard halves were separated along the forward flange and partially separated along the aft flange. The cowling was pulled away from the engine strut, but the engine-to-strut attachment remained intact. Several cowl breaches were observed, concentrated along the upper half. The inner barrel of the inlet cowl had 360-degree circumferential tearing around the engine, in line with the fan plane of rotation, completely detached from the inlet case. The fuselage had organic debris splatter consistent with bird remains forward of the No. 2 engine inlet.
Engine Disassembly and Findings
The engine was shipped to the Pratt & Whitney Canada facility in Bridgeport, West Virginia, for examination. Eleven of the 19 fan blades were found fractured near the blade root. The engine inlet case was separated from the intermediate case, with attachment flange studs sheared or ripped out; a single flange stud and nut held the two cases together at the 5 o'clock position. A chunk of the intermediate case was fractured and missing from the 11 to 2 o'clock positions. Impact damage was observed throughout the low-pressure compressor and booster sections, including a fragmented No. 1 bearing housing. The low-pressure turbine shaft was fractured aft of the high-pressure turbine coupling, and the LPT fuel shutoff valve was tripped, indicating axial displacement.
Metallurgical examination of all 19 fan blades revealed that 11 blades had transverse fractures near the blade platform, with fracture surfaces consistent with ductile overload and no evidence of fatigue. The remaining eight blades exhibited substantial impact deformation and surface cracks, also consistent with overload. Material composition met drawing specifications.
Bird Species Identification
Multiple samples of bird feathers and remains were sent to the Smithsonian Institute and identified as a herring gull. The average mass of this species is 1085 grams (2.39 pounds). Analysis could not determine if more than one bird was ingested.
Modal Testing
Pratt & Whitney Canada conducted modal testing on a JT15D-5 engine installed on a Beechjet 400A. Testing identified a four nodal diameter coincidence between the fan and inlet case at an N1 speed of about 72%. When energy is imparted to the fan by an event like a bird strike, it can result in a rub-induced excitation and catastrophic engine failure.
Corrective Actions
In response to these findings, Pratt & Whitney Canada evaluated inlet case damping options to attenuate the identified natural frequency and planned to complete the design change and introduce the modification to the fleet in 2017.