# NTSB DEN87LA199: Bell 204B, N4580Y, Dubois, WY, July 29, 1987

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Limited investigation · Final report
- Date: July 29, 1987, 09:50 local (15:50 UTC)
- Place: Dubois, WY
- Coordinates: 43.529178, -109.6399 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=43.5292&lon=-109.6399&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious
- Status: Completed, report October 7, 1988
- Report: Approved by Office Director
- NTSB case key (mKey): 17284
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN87LA199
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/17284/pdf
- Page: https://openairdocs.org/ntsb/DEN87LA199

## Sequence of events

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

- Loss of engine power, hover
  - reason for occurrence undetermined (cause)
- Forced landing, descent - emergency
  - autorotation - attempted, pilot in command
- Hard landing, landing - flare/touchdown
  - terrain condition - none suitable (cause)

## Analysis

THE COMMERCIAL PLT WAS PERFORMING EXTERNAL SLING LOADS IN SUPPORT OF SEISMIC OPERATIONS. THE PLT REPORTED THAT THE ENGINE FAILED DURING A LOAD RELEASE AND THE PLT EXECUTED AN AUTOROTATION. THIS RESULTED IN A HARD LANDING IN HEAVY TIMBER ON SLOPING TERRAIN. THE HELICOPTER ROLLED OVER ON THE RIGHT SIDE. A POST ACCIDENT ENGINE INSPECTION REVEALED NO PREIMPACT MECHANICAL MALFUNCTIONS /FAILURES.

## Aircraft

- Registration: [N4580Y](https://openairdocs.org/deregistered/N4580Y-2002-04-29), registration cancelled 2002-04-29, S/N 2066, built 1967 (OpenAirDocs)
- Reported make and model: BELL 204B
- Registry model: [Bell 204-B](https://openairdocs.org/model/bell-204-b) (registry code 1181404) (OpenAirDocs)
- Registry engine: [Lycoming T-53 series](https://openairdocs.org/engine/lycoming-t-53-series) (registry code 41552, turbo-shaft) (OpenAirDocs)
- Category: Helicopter
- Serial number: 2066
- Airframe hours: 4000
- Engines: LYCOMING T-53-L13B 1250 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Other work use, Part 133
- Registered owner: Bill Williams-Southern Aero
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, July 3, 1987, 18 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 35; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 5,200 total, 1,600 in this make and model, 1,600 as pilot in command, 150 in the last 90 days, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 270° at 5 knots
- Visibility: 15 statute miles
- Lowest ceiling: none
- Temperature: 55 °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 19870729046029A](https://openairdocs.org/incident/19870729046029A), Jul 29, 1987: Bell STC204, Dubois, WY, Substantial damage. Engine quit during seismic sling load operations. Auto rotated into trees and rough terrain.

## Other investigations on N4580Y (1)

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 MIA97TA139](https://openairdocs.org/ntsb/MIA97TA139), Apr 16, 1997: Bell 204-B (N4580Y), Calderwood, TN, destroyed. Probable cause: The inadequate maintenance inspection of the helicopter resulting in loss of lubrication from the main drive shaft going undetected until failure of the drive shaft.

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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