Uncontained engine failure: Lancair Legacy 2000, N707MM, registered to Air Horse LLC, and being operated by Michael Patey, incident occurred on July 20, 2023, near Rochester, Minnesota

• Location: Rochester, Minnesota
• Incident Number: ENG23LA034
• Date & Time: July 20, 2023, 14:42 Local
• Registration: N707MM
• Aircraft: HALL LESTER R LEGACY
• Aircraft Damage: Minor
• Defining Event: Uncontained engine failure
• Injuries: 2 None
• Flight Conducted Under: Part 91: General aviation - Air race/show

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/192877/pdf

https://data.ntsb.gov/Docket?ProjectID=192877

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.

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.

- Probable Cause: Mechanically distressed reduction gears causing an engine overspeed and turbine blade tensile overload and subsequent uncontainment. Contributing to the uncontainment was the operator’s use of the engine after knowingly purchasing the engine in an unserviceable condition and only conducting a periodic inspection before flight.