DFW07LA027 · Bell BH 206L-3
Bell BH 206L-3 · Accident: total loss of engine power (mechanical failure) en route
From Abilene Regional Airport (ABI) to Brownwood, TX
Event
- NTSB case
- DFW07LA027
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Bell BH 206L-3
- Aircraft type
- Bell BH-206
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N805SB
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Abilene Regional Airport (ABI), Abilene, TXTo Brownwood, TX
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · descent
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Total loss of engine power (mechanical failure)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Other maintenance personnel › Maintenance, installation, improper
- Turbine assembly, turbine wheel › Overspeed
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The helicopter pilot experienced a sudden "explosion" followed by an uncommanded left yaw while initiating an approach. During the autorotation the pilot was forced to increase collective pitch in order to clear a berm resulting in a loss of main rotor RPM. The helicopter landed hard and remained in the upright position. A review of the turbine engine's maintenance records and work orders revealed the engine had been repaired and inspected in December 2005 for "a sudden stoppage." At that time, the compressor, gearbox, and turbine were replaced. A teardown examination of the engine revealed that the aft end of the turbine-to-compressor coupling had fractured in the region where it mated with the turbine splined adapter. The coupling fracture resulted in a loss of continuity in the N1 drive train and an overspeed failure of the first stage turbine wheel. Metallurgical examination of the fracture surfaces of the remnants of the first stage turbine wheel revealed there was no fatigue fractures. Examination of the splines in the aft end of the coupling and on the pieces from the fractured section revealed fretting and a fractured spline tip in the area of contact with the turbine spline adapter. There was non-uniform wear on 16 consecutive external splines on the turbine splined adapter and there was also non-uniform wear of the splines in the area where the adapter mated with the aft end of the turbine-to-compressor coupling. When the engine was disassembled, there was a discrepancy noted between the thickness of the shims (used for alignment of the gas producer and power turbine drive trains) on the mounting pad between the exhaust collector support and the accessory gearbox than what had been entered in the engine logbook or what was etched on the exhaust collector support. In addition, the balance marks on the spur adapter gear shaft and the turbine-to-compressor coupling were not aligned. According to the Rolls Royce 250-C30 series Overhaul Manual, the balance marks were required to be aligned during re-assembly of the engine. The Overhaul Manual also stated that the cracks found on the vertical fire shield could have been as a result of "abnormally high engine vibration."
Probable cause
The fracture of the turbine-to-compressor coupling and subsequent overspeed failure of the first stage turbine wheel as result of the improper re-assembly of the engine by maintenance personnel. A contributing factor was the lack of suitable terrain for the forced landing.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record DFW07LA027
- Event ID
- 20061205X01734
- Case number
- DFW07LA027
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status, coordinates. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 843c3f4d5b933f3101c5a1165ce7a33181142f8d80a771eb2278fde1a381f898; retrieved 2026-09-22T04:11:47.187Z.