Enstrom F-28F accident near Monmouth, Oregon, March 6, 2007
On March 6, 2007 at about 7:00 pm local time, a Enstrom F-28F (helicopter), registered N785M, was substantially damaged in an accident near Monmouth, Oregon. It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The failure of the main drive belt tension assembly shaft due to high cycle, low stress fatigue.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- March 6, 2007 · about 7:00 pm local time
- Place
- Monmouth, Oregon · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Enstrom F-28F · all F-28Fs on the register
- Registration
- N785M · registry record · serial 785
- Damage
- Substantial damage
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative final · quoted from the NTSB record
The pilot reported that he was spraying Christmas trees, when the engine experienced an over speed condition and he "lost all power to the transmission." The pilot initiated a forced landing to a field. During the forced landing, the helicopter touched down hard and bent the tail boom. The pilot stated that the engine was producing power, but it wasn't being delivered to the rotor blades. Examination of the helicopter revealed the shaft of the main drive belt tension assembly was fractured, which resulted in the main drive belt disengaging from the transmission. Materials examination of the shaft showed that the shaft fractured due to high cycle, low stress fatigue. The fatigue initiated from multiple origins at the thread root. No material defects specific to the origin were noted, but overall hardness values suggested that the shaft strength was less than typical strength values for the specified material. It remained undetermined whether the strength was above the design minimum since no material specifications for the shaft could be produced by the manufacturer.
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
Pilot
- Certificate: commercial pilot, private
- Ratings: single-engine land; rotorcraft: helicopter
- Flight time: 8,017 hours in all; 7,817 in this make and model; 25 in the last 90 days; 20 in the last 30 days; 7,967 as pilot in command
- Last flight review: January 1, 2007
- Medical certificate: Class 2 (without waivers/limitations)
- Seat: left
- Injury: no injuries
The aircraft
- Airframe total time: 2,393.2 hours
- Last inspection: annual inspection, January 1, 2007
- Maximum gross weight: 2,600 lb
- Seats: 3
- Landing gear: fixed
- Engine: Lycoming HIO-360-F1AD (piston); 0 hours total
The flight
- Departed from: Monmouth OR at 6:50 pm
- Destination: Corvalis OR
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 180° at 3 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 54°F (12°C), dew point 45°F (7°C)
- Altimeter: 30.10 inHg
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.