Amateur-built DRAGONFLY accident near Avon, Montana, September 30, 1998
On September 30, 1998 at about 3:45 pm local time, a amateur-built DRAGONFLY, registered N4478V, was destroyed in an accident near Avon, Montana. It was a personal flight under general aviation rules (Part 91). 1 person had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
Failure of the engine crankshaft aft oil seal resulting in the loss of engine oil, and rough terrain during the forced landing.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 30, 1998 · about 3:45 pm local time
- Place
- Avon, Montana · map
- Type
- Accident
- Injuries
- 1 person had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built DRAGONFLY
- Registration
- N4478V · no longer on the register · serial 437
- Damage
- Destroyed
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot-in-command/owner of the homebuilt Volkswagen-engine powered Dragonfly departed Helena, Montana, uneventfully. After approximately 30 minutes of flight he observed the engine oil pressure decrease to zero in less than two minutes with a concurrent increase in oil temperature. He then executed a forced landing in a rough pasture during which the aircraft bounced and then cartwheeled. Post-crash examination revealed oil on the aircraft's firewall and underside. Further examination revealed that the engine rear crankshaft seal was deformed and the neoprene gasket was missing.
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: private
- Ratings: single-engine land
- Flight time: 1,170 hours in all; 850 in this make and model; 40 in the last 90 days; 15 in the last 30 days; 1,120 as pilot in command
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 988 hours
- Last inspection: annual inspection, March 4, 1998; 41 hours since
- Maximum gross weight: 1,175 lb
- Seats: 2
- Landing gear: fixed
- Engine: Volkswagen (piston); 0 hours total
The flight
- Departed from: HLN Helena MT at 3:15 pm
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 300° at 5 knots
- Visibility: 10 statute miles
- Sky: overcast at 4,000 ft; not recorded
- Temperature: 48°F (9°C), dew point 39°F (4°C)
- Altimeter: 30.00 inHg
- Observation at 3:56 pm from HLN, 25 miles away
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.
Other NTSB records under N4478V the same tail number, which may have belonged to a different aircraft at the time
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.