# NTSB SEA92LA029: Aerospatiale AS355F1, N101UC, Billings, MT, October 29, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: October 28, 1991, 19:15 local (Oct 29, 1991, 02:15 UTC)
- Place: Billings, MT
- Coordinates: 45.870731, -108.470985 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=45.8707&lon=-108.4710&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 3 uninjured
- Status: Completed, report May 27, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 41617
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA92LA029
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41617/pdf
- Page: https://openairdocs.org/ntsb/SEA92LA029

## Probable cause

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.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, cruise
  - door,inspection - unlatched (cause)
  - maintenance,service bulletin/letter - not performed, company maintenance personnel (contributing factor)

## Analysis

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.

## Aircraft

- Registration: [N101UC](https://openairdocs.org/deregistered/N101UC-2000-06-26), registration cancelled 2000-06-26, S/N 5186 (OpenAirDocs)
- Reported make and model: AEROSPATIALE AS355F1
- Registry model: [Aerospatiale AS 355 F ECUREUIL](https://openairdocs.org/model/aerospatiale-as-355-f-ecureuil) (registry code 8680806) (OpenAirDocs)
- Category: Helicopter
- Serial number: 5186
- Engines: ALLISON 250-C20 420 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Part 91
- Operator: Omni Flight Helicopters, Inc
- Departed: MT25, BILLINGS, MT
- Flight plan: Company VFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 46; commercial; airplane ratings: single-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--no waivers/lim.; flight hours: 2,826 total, 154 in this make and model, 2,513 as pilot in command, 59 in the last 90 days, 21 in the last 30 days

## Weather

- Conditions: Visual (VMC), Night/dark
- Wind: 220° at 4 knots
- Visibility: 20 statute miles
- Lowest ceiling: 2,800 ft broken
- Temperature: -0 °F, dew point -0 °F

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19911028054699A](https://openairdocs.org/incident/19911028054699A), Oct 28, 1991: Aerosp AS355F, Billings, MT, Substantial damage. Engine service door opened in flight. Was severed by contact with main rotors. Crew unaware. Bulletin not complied.

## Other investigations on N101UC (2)

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

- [NTSB NYC97LA058](https://openairdocs.org/ntsb/NYC97LA058), Mar 5, 1997: Aerospatiale AS-355F (N101UC), Washington, PA, substantial damage. Probable cause: The malfunction of a cyclic servo which resulted in a cyclic hard over at a hover.
- [NTSB ATL88IA171](https://openairdocs.org/ntsb/ATL88IA171), May 13, 1988: Aerospatiale AS-355-F (N101UC), Reidsville, NC, incident, minor damage

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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