Event Details
On December 31, 2021, at about 1715 eastern standard time, a Cessna 501 airplane, registration N75TL, equipped with two Pratt & Whitney Canada JT15D-1A turbofan engines, experienced an uncontained failure of the No. 1 (left) engine during takeoff roll from Miami-Opa Locka Executive Airport (OPF) in Opa-Locka, Florida. The pilot was not injured, and post-event examination revealed damage limited to the No. 1 engine and its nacelle structure. The aircraft was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
Engine Examination and Disassembly
The incident engine, serial number PCE-76844, was shipped to the Pratt & Whitney Canada facility in Bridgeport, West Virginia, for examination and disassembly. Upon receipt, the fan was loosely secured in the fan case with a board and zip ties. A trash bag containing engine fragments, including a recovered section of the high pressure compressor (HPC) impeller and assorted small debris from the engine nacelle and runway, was also in the shipping container.
All fan blades exhibited leading edge material loss and tip bending opposite the direction of rotation. A hole in the engine outer bypass duct extended from the 8 to 1 o'clock positions, 14 inches axially at 12 o'clock and 9 inches axially at 8 o'clock, coincident with the HPC impeller plane of rotation. The edges of the hole were petaled outward, consistent with high-energy radial uncontainment.
The HPC impeller was separated into two major segments and three additional small pieces. The larger section, about two-thirds of the impeller circumference, was loose inside the engine. All remaining HPC impeller vanes exhibited impact damage, deformation, and material tearing. The HPC impeller failure resulted in secondary impact damage throughout the engine gaspath, including a sheared low pressure shaft.
Metallurgical Analysis
The HPC impeller, part number 3020365, was shipped to the Pratt & Whitney Canada Materials Investigation Laboratory in Montreal, Quebec, Canada, for metallurgical analysis. The analysis identified a low cycle fatigue crack that initiated along a circumferential machining groove on the aft face of the HPC impeller. Fluorescent penetrant inspection revealed multiple indications along the groove where the fatigue crack initiated and propagated. No material anomalies were found near the crack origin, and the HPC impeller met drawing requirements for part geometry and material specification. A crack striation count estimated the HPC impeller had accumulated approximately 6,380 cycles between crack initiation and overload failure. The striation count also determined that a 1/32-inch surface crack would have formed at approximately 1,970 cycles. The machining grooves on the HPC impeller would have passed overhaul inspection criteria except for impact damage related to the event.
Corrective Actions
In response to the investigation, Pratt & Whitney Canada released service bulletin SB 7655 on April 14, 2022, applicable to all JT15D-1/-1A/-1B engines with HPC impeller part number 3020365 installed. The service bulletin has a compliance category of 3, recommending completion at the next scheduled engine hot section inspection or when Flange C is separated. The bulletin references special instruction SI 38-022 with improved endoscopic fluorescent penetrant inspection procedures. Transport Canada was briefed on the proposed corrective action in February 2022 and subsequently formed a Corrective Action Review Board, ruling that the inspections called out in SB 7655 would be mandated by an airworthiness directive (AD), tentatively scheduled for release in the second quarter of 2022. The Federal Aviation Administration concurred with the proposed Transport Canada AD and began the process of issuing an equivalent AD for United States-registered airplanes with JT15D-1/1A/1B engines. The population of affected engines was estimated by the manufacturer to be 334.