ENG23LA034

Factual narrative

On July 20, 2023, at about 1:42pm local time, a Lancair Legacy airplane, registration number N707MM, powered by a single Pratt & Whiteny Canada PT6A-42 turbo-propeller engine experienced an uncontained engine failure while enroute from the Rapid City Regional Airport (KRAP), South Dakota to the Rochester International Airport (KRST), Minnesota. The pilot declared an emergency, started a gliding descent into KRST, and made a successful landing without power. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 flight. The pilot and passenger reported no injuries. A post flight inspection of the airframe revealed minor impact marks on the wing leading edges from exiting engine debris. A further inspection of the engine revealed an exit hole in the engine. The exhaust ducts exhibited pock marks, consistent with released internal rotating engine parts. An inspection made through the exhaust duct revealed that all the 2nd stage power turbine (PT) blades were fractured near the blade platform. The engine was shipped to the Pratt & Whitney Canada facility in St. Hubert, Quebec, Canada where it was torn down. The findings were: - The engine was in poor overall condition with missing surface protective paint and surface corrosion noted throughout the external and internal surfaces of the engine. - The teeth of the reduction gearbox (RGB) 1st stage sun gear were ground away in the plane of the mating gear teeth of the 1st stage planet gears. The gear teeth of the three planet gears were battered and fractured. - All the blades of the 2nd stage PT were fractured near the root. The fracture surfaces of all the blades exhibited only evidence of tensile overload. The 2nd stage PT hub was intact. - All the blades of the 1st stage PT were fractured at various span heights. The fracture surfaces of all the blades exhibited only evidence of tensile overload. The 1st stage PT hub was intact. - The magnitude and type of damage observed on the 1st and 2nd stage PTs is consistent with a PT overspeed event. - All the compressor turbine (CT) blades were present; however, they were thermally eroded at the tips. The CT hub was intact. - The fuel control unit (FCU) was tested and was very close to nominal production calibration. The engine was purchased by the operator on July 8, 2023, 12 days before the event. A review of the purchase document revealed that the engine was in an unserviceable condition. According to the one-page logbook, only a 200-hour periodic inspection was conducted before the flight. The 200-hour periodic inspection consists of an examination of the engine controls and rigging mechanism, a functional test and inspection of the ignition and chip detector systems, and servicing of oil and inspection of pneumatic and fluids filters. Inspection of the RGB gears is not part of the 200-hour periodic inspection. The RGB gears are inspected during overhaul of the power section. For additional information about the examination of the engine, please see the public docket for this accident. The teeth of the 1st stage sun gear in the reduction gearbox were ground away in the plane of the mating gear teeth of the 1st stage planet gears. The mating gear teeth of the three planet gears were battered and fractured. Distress of the 1st stage sun gear teeth released the torque normally transferred to the propeller, causing the power turbines to overspeed and the power turbine blades to release in tension and become uncontained. It was unknown when the last inspection of the reduction gearbox was performed. During the post incident examination of the engine at the P&WC facility, the engine was found to be in poor overall condition with missing surface protective paint and surface corrosion noted throughout the external and internal surfaces of the engine. A review of the purchase documentation revealed that the operator knowingly purchased the engine in unserviceable condition and only performed a periodic inspection before flight. Source: NTSB Aviation Accident Database Retrieved: 2026-02-12

NTSB Findings

FAA avdata. C = Cause, F = Factor.

• — Aircraft-Aircraft power plant-Engine (turbine/turboprop)-Reduction gear and shaft-Not serviced/maintained