Event
On July 20, 2023, at about 1:42 p.m. local time, a Lancair Legacy airplane, registration N707MM, experienced an uncontained engine failure while en route from Rapid City Regional Airport (KRAP), South Dakota, to Rochester International Airport (KRST), Minnesota. The single Pratt & Whitney Canada PT6A-42 turbo-propeller engine failed. The pilot declared an emergency, initiated a gliding descent, and landed successfully at KRST without power. The flight was conducted under Title 14 Code of Federal Regulations Part 91. The pilot and passenger reported no injuries.
Post-flight Inspection
A post-flight inspection revealed minor impact marks on the wing leading edges from exiting engine debris. The engine casing showed an exit hole, and the exhaust ducts had pock marks consistent with released internal rotating parts. Inspection through the exhaust duct indicated that all second-stage power turbine (PT) blades were fractured near the blade platform.
Engine Teardown
The engine was shipped to Pratt & Whitney Canada in St. Hubert, Quebec, for teardown. Findings included: poor overall condition with missing surface protective paint and corrosion on external and internal surfaces; the reduction gearbox (RGB) first-stage sun gear teeth were ground away, and the first-stage planet gear teeth were battered and fractured; all second-stage PT blades were fractured near the root, with fracture surfaces showing only tensile overload (the hub was intact); all first-stage PT blades were fractured at various span heights, also with tensile overload evidence (hub intact); the damage pattern was consistent with a PT overspeed event; compressor turbine blades were present but thermally eroded at the tips (hub intact); the fuel control unit tested near nominal production calibration.
Additional Information
The engine was purchased by the operator on July 8, 2023, 12 days before the event. The purchase document indicated the engine was in an unserviceable condition. According to a one-page logbook, only a 200-hour periodic inspection was conducted before the flight. That inspection includes checks of engine controls, rigging, ignition and chip detector systems, and servicing of oil and filters; it does not involve inspection of RGB gears. RGB gears are inspected during power section overhaul.