Enstrom F-28A accident near Leroy, Minnesota, August 23, 2004
On August 23, 2004 at about 2:50 pm local time, a Enstrom F-28A (helicopter), registered N9573, was substantially damaged in an accident near Leroy, Minnesota. It was an aerial observation flight under general aviation rules (Part 91). 1 person was seriously injured. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The partial loss of engine power due to the missing 1/8-27 NPT Allen plug as a result of other maintenance personnel undertorquing the plug. Additionally, the pilot improperly excecuted a run on landing. A factor was the loss of tail rotor effectiveness.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- August 23, 2004 · about 2:50 pm local time
- Place
- Leroy, Minnesota · map
- Type
- Accident
- Injuries
- 1 person was seriously injured.
- Weather
- visual conditions (good weather)
- Aircraft
- Enstrom F-28A · all F-28As on the register
- Registration
- N9573 · registry record · serial 131
- Damage
- Substantial damage
- Flight
- Aerial observation flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The helicopter sustained substantial damage when it impacted terrain and rolled over after a loss of engine power during takeoff. The pilot reported that the engine was producing 3,000 rpm's when he brought the helicopter into a hover. He transitioned into forward flight and cleared a fence, and then the engine lost power. He reported that he thought that an exhaust valve was stuck. He attempted to do a run on landing to a field. The helicopter touched down on its left skid two times but the helicopter was not straight. He reported that the third time the helicopter touched down on its left skid, the helicopter was not straight and the rpm's were low. He reported that he ran out of tail rotor authority. The helicopter rolled over on its left side. The engine was inspected and an engine run was conducted. The engine was run at 1,800 to 2,000 rpm, and then at 1,110 to 1,200 rpm; but the engine popped and ran unevenly. A re-inspection of the engine revealed that the 1/8-27 NPT Allen plug to the number four cylinder was missing. Once the hole was plugged, the engine ran smoothly.
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
Co-pilot
- Certificate: commercial pilot
- Ratings: multi-engine land; single-engine land; instrument: airplane; rotorcraft: helicopter
- Flight time: 50,000 hours in all; 7,000 in this make and model; 100 in the last 90 days; 30 in the last 30 days
- Medical certificate: Class 2
The aircraft
- Landing gear: fixed
- Engine: Lycoming HIO-360-CIA (piston); 0 hours total
- Operator: P & N Corporation
The flight
- Departed from: Leroy MN at 2:48 pm
- Flight plan: none
Weather at the time
- Light: daylight
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
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.