Bell 206L-1 accident near Busby, Montana, August 3, 2006
On August 3, 2006 at about 6:30 pm local time, a Bell 206L-1 (helicopter), registered N5746N, was substantially damaged in an accident near Busby, Montana. It was a public-use flight (federal) under general aviation rules (Part 91). No one was hurt; 4 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The improper overhaul of the turbine assembly by maintenance personnel, which resulted in failure of the turbine and a total loss of engine power. A contributing factor was the pilot's misjudgment of the landing flare at the termination of the autorotation.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- August 3, 2006 · about 6:30 pm local time
- Place
- Busby, Montana · map
- Type
- Accident
- Injuries
- No one was hurt; 4 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 206L-1 · all 206L-1s on the register
- Registration
- N5746N · no longer on the register · serial 45461
- Damage
- Substantial damage
- Flight
- Public-use flight (federal) · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot reported that the helicopter's engine failed during performance of a power assurance check. Prior to beginning the power check, the pilot established straight and level flight at 90 knots and 8,000 feet msl (about 5,000 feet agl). He increased collective, the helicopter began to climb, and at approximately 8,300 to 8,400 feet msl and a torque reading of 95%, there was a loud grinding noise and the engine lost power. The pilot entered an autorotation. During touchdown in an open field, the main rotor struck and severed the tail boom. Examination of the engine determined that the turbine exhibited internal damage and would not rotate. Disassembly of the turbine section revealed rub damage to all the blade tips on the first and second stage turbine wheels. Corresponding rub damage was noted to the blade paths in the second stage turbine nozzle for these turbine wheels. A single blade was separated from the second stage turbine wheel. There was severe damage to the turbine wheels and nozzles located downstream of the second stage turbine wheel. Metallurgical examination found that the second stage turbine nozzle assembly second stage blade path had been dimensionally restored using thermal spray material. The coating exhibited unmelted particles, oxides, and was separated from the base metal at both forward and aft ends. The defects in the coating resulted in blade tip rub and led to the fatigue failure of a blade, which separated and destroyed the downstream turbine wheels and nozzles. Review of the helicopter's maintenance records indicated that the engine's turbine section was replaced with a repaired unit approximately 13 flight hours prior to the accident. During the repair of the turbine, dimensional restoration of the second stage turbine nozzle second stage blade path was performed.
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: flight instructor, commercial pilot
- Ratings: multi-engine land; single-engine land; instructor: helicopter; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 6,000 hours in all; 3,500 in this make and model; 140 in the last 90 days; 85 in the last 30 days; 6,000 as pilot in command
- Last flight review: June 1, 2006
- Medical certificate: Class 2 (with waivers/limitations)
- Seat: rgt
- Injury: no injuries
The aircraft
- Airframe total time: 12,138 hours
- Last inspection: 100-hour inspection, July 1, 2006; 13 hours since
- Maximum gross weight: 4,150 lb
- Seats: 6
- Landing gear: fixed
- Engine: Rolls-Royce 250-C30P (turboshaft); 0 hours total
The flight
- Departed from: Busby MT at 6:00 pm
Weather at the time
- Light: daylight
- Wind: from 360° at 4 knots
- Visibility: 30 statute miles
- Sky: clear
- Temperature: 86°F (30°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 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.
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.