ENG23LA034 · Hall Lester R LEGACY
Hall Lester R LEGACY · Incident: uncontained engine failure en route
From Rapid City Regional Airport (KRAP) to Rochester International Airport (KRST)
Event
- NTSB case
- ENG23LA034
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Incident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- Event fatalities
- Unknown
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Hall Lester R LEGACY
- Aircraft type
- Hall Lester LEGACY
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N707MM
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Rapid City Regional Airport (KRAP), Rapid City, SDTo Rochester International Airport (KRST), Rochester, MN
- Aircraft age
- About 20 years (built 2003)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Uncontained engine failure
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Minor
Cause areas
- Aircraft › Aircraft power plant
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
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.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ENG23LA034
- Event ID
- 20230815192877
- Case number
- ENG23LA034
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status, coordinates, cause areas. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: edbed57fe90885a643f42b2f06b6e735b9b984d479325dd7727e3162a4395412; retrieved 2026-09-16T18:00:28.619Z.