Amateur-built LEGACY incident near Rochester, Minnesota, July 20, 2023
On July 20, 2023 at about 7:42 pm local time, a 2003 amateur-built LEGACY, registered N707MM, suffered minor damage in an incident during enroute near Rochester, Minnesota (Rochester International Airpor airport). It was an air show or air race flight under general aviation rules (Part 91). No one was hurt; 2 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 20, 2023 · about 7:42 pm local time
- Place
- Rochester, Minnesota · Rochester International Airpor · map
- Type
- Incident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built LEGACY, built 2003
- Registration
- N707MM · registry record · serial L2K-221
- Damage
- Minor damage
- Flight
- Air show or air race flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Uncontained engine failure during enroute defining event
The NTSB's findings
- Aircraft › Aircraft power plant › Engine (turbine/turboprop) › Reduction gear and shaft › Not serviced/maintained
Pilot
- Certificate: commercial pilot, private
- Ratings: multi-engine land; single-engine land; single-engine sea; instrument: airplane; rotorcraft: helicopter
- Medical certificate: Class 2 (without waivers/limitations)
- Seat: left
- Injury: no injuries
Passenger
- Seat: rgt
- Injury: no injuries
The aircraft
- Airframe total time: 613.7 hours
- Last inspection: annual inspection, July 11, 2023
- Maximum gross weight: 3,000 lb
- Seats: 2
- Landing gear: retractable
- Engine: Pratt & Whitney Canada PT6A-42 (turboprop); 0 hours total
The flight
- Departed from: KRAP Rapid City SD
- Destination: KRST Rochester MN
- Flight plan: IFR
Weather at the time
- Light: daylight
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 2 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
1 document, released by the NTSB on August 14, 2025. View them here, or download them; the NTSB redacts some personal details before release, and this site shows the NTSB's own titles rather than its file names.
| # | Document | What it is | |
|---|---|---|---|
| 1 | Powerplants Factual Report | PDF, 24 pages | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.