# NTSB SEA90LA137: Sikorsky S-58BT, N439DS, Ovando, MT, July 16, 1990

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: July 16, 1990, 10:30 local (16:30 UTC)
- Place: Ovando, MT
- Coordinates: 47.069293, -113.040496 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=47.0693&lon=-113.0405&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report December 8, 1992
- Report: Approved by Office Director
- NTSB case key (mKey): 41241
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA90LA137
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41241/pdf
- Page: https://openairdocs.org/ntsb/SEA90LA137

## Probable cause

THE PILOT DID NOT MAINTAIN ROTOR RPM AFTER A COMPRESSOR ASSEMBLY BLADE FAILURE. A RELATED FACTOR WAS AN INADEQUATE AUTOROTATION RESULTING IN A HARD LANDING.

## Sequence of events

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

- Loss of engine power(total) - mech failure/malf, hover
  - compressor assembly,blade - failure,total (cause)
  - rotor rpm - not maintained, pilot in command (cause)
- Forced landing, descent - emergency
- Hard landing, landing - flare/touchdown
  - autorotation - inadequate, pilot in command (contributing factor)

## Analysis

DURING AN EXTERNAL LOAD LOGGING OPERATION, THE PILOT HAD JUST TAKEN OFF FROM REFUELING AND WAS PREPARING FOR ANOTHER LOAD PICK- UP WHEN THE NUMBER ONE ENGINE LOST POWER AND FLAMES WERE OBSERVED SHOTTING OUT FROM THE EXHAUST. THE PILOT TRIED TO FLY THE HELICOPTER ON ONE ENGINE TO A LANDING AREA, HOWEVER, RPM WAS DROPPING. THE PILOT INITIATED AN AUTOROTATION WHICH RESULTED IN A HARD LANDING.

## Aircraft

- Registration: [N439DS](https://openairdocs.org/deregistered/N439DS-2000-11-02), registration cancelled 2000-11-02, S/N 58658 (OpenAirDocs)
- Reported make and model: SIKORSKY S-58BT
- Registry model: [Sikorsky S-58BT](https://openairdocs.org/model/sikorsky-s-58bt) (registry code 8141840) (OpenAirDocs)
- Category: Helicopter
- Serial number: 58-658
- Engines: P&W T400-CP-400 900 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Other work use, Part 133
- Operator: Skyline Helicopters
- Departed: CANYON CREEK, MT

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 39; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--no waivers/lim.; flight hours: 6,298 total, 1,248 in this make and model, 6,000 as pilot in command

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 50 statute miles
- Lowest ceiling: none
- Temperature: 86 °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 19900716026329A](https://openairdocs.org/incident/19900716026329A), Jul 16, 1990: Skrsky S58BT, Ovando, MT, Substantial damage. NR1 engine failed at hover and fire from tailpipe. Delayed autorotation. Hard landing. Engine overheated in hover.

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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