Aerospatiale AS355F1 accident near Billings, Montana, October 29, 1991
On October 29, 1991 at about 2:15 am local time, a Aerospatiale AS355F1 (helicopter), registered N101UC, was substantially damaged in an accident near Billings, Montana. It was a flight of an unrecorded kind under general aviation rules (Part 91). No one was hurt; 3 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
THE UNLATCHING AND SUBSEQUENT OPENING INFLIGHT OF THE LEFT-REAR ENGINE COWL DOOR. A FACTOR CONTRIBUTING TO THE ACCIDENT WAS THE FAILURE OF COMPANY MAINTENANCE PERSONNEL TO EXECUTE THE MANUFACTURER'S SERVICE BULLETIN.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- October 29, 1991 · about 2:15 am local time
- Place
- Billings, Montana · map
- Type
- Accident
- Injuries
- No one was hurt; 3 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Aerospatiale AS355F1 · all AS355F1s on the register
- Registration
- N101UC · no longer on the register · serial 5186
- Damage
- Substantial damage
- Flight
- Flight of an unrecorded kind · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
SHORTLY AFTER THE COMPANY INITIATED ABORT OF THE MEDEVAC FLIGHT, THE FLIGHT CREW OF THE AEROSPATIALE AS355 FELT A SHUDDER WHICH THEY ATTRIBUTED TO GUSTY WIND CONDITIONS. UPON LANDING AT BILLINGS INTERNATIONAL AIRPORT, MONTANA, A PORTION OF THE LEFT-REAR ENGINE COWL DOOR WAS FOUND TO BE SEPARATED, ALONG WITH DAMAGE TO THE MAIN ROTOR BLADES NECESSITATING REPLACEMENT OF THE BLADES. THE CREW HAD PREVIOUSLY NOTIFIED COMPANY PERSONNEL OF THE COWL DOOR LATCH PROBLEM AND HAD PREFLIGHTED THE COWL PRIOR TO THE ACCIDENT FLIGHT. THE MANUFACTURER WAS AWARE OF THE PROBLEM AND HAD ISSUED A RELEVANT SERVICE BULLETIN. THE SERVICE BULLETIN HAD NOT BEEN IMPLEMENTED ON THE ACCIDENT AIRCRAFT.
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
- Ratings: single-engine land; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 2,826 hours in all; 154 in this make and model; 59 in the last 90 days; 21 in the last 30 days; 2,513 as pilot in command
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: unk
The aircraft
- Last inspection: inspection type not recorded; 0 hours since
- Maximum gross weight: 5,291 lb
- Seats: 5
- Landing gear: fixed
- Engine: Allison 250-C20 (turboshaft); 0 hours total
- Operator: Omni Flight Helicopters, INC
The flight
- Departed from: MT25 Billings MT
- Runway 0
Weather at the time
- Light: night, dark
- Wind: from 220° at 4 knots
- Visibility: 20 statute miles
- Sky: broken clouds at 2,800 ft; not recorded
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 3 |
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 N101UC 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.