Incident
On December 5, 2016, at approximately 1123 central standard time, a Cessna 550 airplane, registration N75WL, struck ducks during climb-out from Mustang Beach Airport (RAS) in Port Aransas, Texas. The right engine subsequently lost power. The pilot diverted to Corpus Christi International Airport (CRP) in Corpus Christi, Texas, where an uneventful landing was made. The pilot was not injured. The aircraft was registered to and operated by DC Aviation, LLC under 14 CFR Part 91. Instrument meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan. The flight originated from RAS and was destined for Fort Worth Meacham International Airport (FTW) in Fort Worth, Texas.
Examination
The airplane sustained substantial damage to the right engine, fuselage, and right wing. Examination at CRP revealed both engines were in place with inlet ducts and cowlings secure. The left engine had no damage, though two small spatters of bird remains were found on the inlet duct lip. The right engine's fan and booster stages were completely missing from the front, but the cowling had no holes. The inlet duct interior was torn at the aft end with circumferential scoring marks spiraling outward. The duct interiors were coated with bird remains. The left side of the nose near the cargo compartment door had a streak of bird remains. The right fuselage had a cluster of holes and bird remains just forward of the engine and above the wing. The right wing forward of the engine over the rear spar had circumferential gouges, some penetrating the upper surface into the right main landing gear wheel well, though hydraulic lines beneath were undamaged.
Bird remains from the right engine's fan duct were collected and sent to the Smithsonian Institution's Feather Identification Laboratory. DNA analysis identified the bird as a redhead duck, a medium-sized diving bird weighing between 1.38 and 3.31 pounds, indigenous to Gulf coastal waters in winter.
The right engine was removed for further examination. The fan and booster stage rotor assembly was later found by a citizen in a marsh near RAS and retained for analysis.
Engine Details
Examination of the fan and booster stages showed both disks intact with all blades in their slots. Eight of the 28 fan blades were fractured transversely adjacent to the blade root platform; fractures were coarse, grainy, with shear lips. The remaining fan blades were fractured at the mid-span shrouds. A 120° arc of blades was bent opposite the rotor rotation direction. Two blades, about 155° apart, had large-radius curvatures on their leading edges. Metallurgical examination followed.
The remainder of the engine showed no evidence of uncontainment, case rupture, or fire. The fan case was intact with circumferential scoring and gouging, and three distinct bulges. The low-pressure compressor (LPC) drive shaft was broken into three pieces. The aft broken end had a heavy circumferential rub with heat check cracking, material transfer, and resolidified metal on the shaft interior, oriented to one side. The No. 1 bearing housing was broken into two pieces, and its cover shattered. Bird remains were on the intermediate case struts. The high-pressure compressor impeller was intact, but its vanes had numerous nicks and dents with missing leading edge pieces. The combustor case had metal splotches on the dome and exterior, with no bird remains in the combustor area. Metal slag was built up around the high-pressure turbine nozzles. The emergency fuel shut-off valve plunger was extended, indicating the valve was in the cut-off position.
The JT15D-4 engine was certificated in Canada to 14 CFR Part 33 Amendments 1–4 and Advisory Circulars 33-1B and 33-3. It is similar in design to the JT15D-1 engine. The Canadian Department of Transport permitted Pratt & Whitney Canada to use the JT15D-1 engine's large bird strike certification test for the JT15D-4. During that test, a 4-pound chicken was propelled into the engine at 495 feet per second (293 knots). The engine stopped abruptly, and five fan blades broke, penetrating the aluminum fan case. The certification report stated that all shafts, rotors, and other rotating elements remained within the engine. As a result, Pratt & Whitney Canada replaced the aluminum fan case with a steel fan case, which was carried over to the JT15D-4.
Metallurgical examination of the LPC drive shaft fractures showed shear and ductile tensile overloads in a twisting direction opposite rotor rotation. The lab report suggested the fracture was consistent with the forward part of the shaft experiencing a deceleration force relative to the turbine end. The eight fan blades broken adjacent to the root platform were due to ductile bending overload with no indications of fatigue.