HISTORY OF FLIGHT
On May 13, 2014, at about 1511 central daylight time, a Raytheon Beechjet 400A, N412GJ, equipped with two Pratt & Whitney Canada (PWC) JT15D-5 engines, experienced a No. 2 engine fire following a bird strike during takeoff roll at Sugar Land Regional Airport (SGR), Sugar Land, Texas. The crew successfully aborted the takeoff and came to a full stop on the runway. Both fire bottles were discharged and the fire was extinguished. During a survey of the aircraft, fuel was found leaking from the No. 2 engine cowling and from a puncture in the right wing fuel tank at the wing fence between the wing and fuselage. The No. 2 engine fan blades were all fractured near the root and there was evidence of blade fragments impacting the inlet cowl forward of the fan. The flight was being operated in accordance with 14 Code of Federal Regulations Part 91 to reposition the airplane.
INJURIES
No injuries were reported to passengers or crew.
DAMAGE TO AIRPLANE
An on scene examination of the airplane and No. 2 engine cowling was conducted by representatives from the Federal Aviation Administration (FAA) Houston Flight Standards District Office (FSDO) and Textron Aviation. The No 2 engine core cowl had multiple breaches and bulges around the engine consistent with radial release of engine fragments. The core cowl also exhibited thermal distress including paint bubbling and deformation, most concentrated on the top half. Paint blistering was observed on the No. 2 engine strut. The right wing had multiple small impact marks forward of the engine inlet. One of the impacts at the wing fence penetrated the right fuel tank resulting in a fuel leak.The inner barrel of the inlet cowl exhibited extensive circumferential tearing in line with the fan plane of rotation and gouging and impact damage along the length of the cowl. The inlet cowl damage partially separated the inlet cowl from the engine.
TEST AND RESEARCH
Engine Examination
The No. 2 engine was shipped to the PWC facility in Bridgeport, West Virginia for examination and teardown. All 19 fan blades were fractured and separated near the blade platform. Seventeen (17) of the 19 separated blade airfoils were recovered in the engine or on the runway. The engine inlet case was ovalized and the outer diameter of the case exhibited impact damage. The inlet case also had a 360 degree circumferential fracture that allowed the forward section of the case to separate from the engine and was found hanging loosely. The intermediate case was pulled away from the inlet case where the attaching bolts failed between the 7 and 1 o'clock positions and had a series of circumferential and axial cracks.
Metallurgy
Nineteen (19) fan blade platforms and seventeen (17) fan blade airfoils that were recovered were submitted to the PWC Materials Lab in Longueuil, Quebec, Canada for examination. All blades had transverse factures near the blade platform. Binocular and scanning electron microscopy (SEM) examination determined that all fracture surfaces were consistent with ductile overload and no indications of fatigue were observed.
Bird Species Identification
A sample of bird feathers and remains (snarge) were sent to the Smithsonian Institute in Washington, DC for species identification. The remains were positively identified to be a yellow-crowned night-heron. The average mass of this species is 683g (1.51lbs). The analysis could not determine if more than one bird was ingested.
Modal Testing
PWC completed a series of tests to determine the root cause of the dynamic response between the fan and inlet case following the birdstrike event. Modal testing was done at both the component and engine level with tap hammers and high energy shakers. Tests were also conducted to measure the sensitivity of the engine to varying levels of stiffness at the engine to inlet case attachment. Finally, tap hammer testing was performed on a JT15D-5 engine installed on a Beechjet 400A representative of the incident airplane. The testing identified a four nodal diameter coincidence between the fan and inlet case at an N1 speed of about 72%. Both the fan and inlet case share a natural frequency at about 72% N1 speed and when energy is imparted to the components by an event like a birdstrike, it can result in a rub induced excitation and catastrophic engine failure. ADDITIONAL INFORMATION
Corrective Actions
In response to these findings, PWC is evaluating inlet case damping options to attenuate the identified natural frequency and plans to complete the design change and introduce the modification to the fleet in 2017.