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Accidents · NTSB SEA90LA137 · Final report

Sikorsky S-58BT accident near Ovando, Montana, July 16, 1990

On July 16, 1990 at about 4:30 pm local time, a Sikorsky S-58BT (helicopter), registered N439DS, was substantially damaged in an accident near Ovando, Montana. It was an other work-use flight under external-load helicopter rules (Part 133). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).

The NTSB's probable cause their words, unchanged

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.

Source: NTSB aviation accident database, copy made November 2, 2026. Docket and reports at the NTSB.

What the record shows

Date
July 16, 1990 · about 4:30 pm local time · cases in 1990
Place
Ovando, Montana · map
Type
Accident
Injuries
No one was hurt; 1 person was on board or involved.
Weather
visual conditions (good weather)
Aircraft
Sikorsky S-58BT · all S-58BTs on the register
Registration
N439DS · registry record · serial 58-658
Damage
Substantial damage
Flight
Other work-use flight · external-load helicopter rules (Part 133)

The NTSB's narrative final · quoted from the NTSB record

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.

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: multi-engine land; single-engine land; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
  • Flight time: 6,298 hours in all; 1,248 in this make and model; 6,000 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: 12,500 lb
  • Seats: 2
  • Landing gear: fixed
  • Engine: P&W T400-CP-400 (turboshaft); 0 hours total

The flight

  • Departed from: Canyon Creek MT at 4:15 pm
  • Flight plan: none
  • Runway 0

Weather at the time

  • Light: daylight
  • Visibility: 50 statute miles
  • Sky: clear
  • Temperature: 86°F (30°C), dew point 0°F (-18°C)

Injuries

FatalSeriousMinorNone
Crew1

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.

Connections how this case links to the rest of the register

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The whole map of how records connect · these connections as data: /graph/accident/SEA90LA137.json.

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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 does not name anyone involved, its policy at this time. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.