ANC98TA125 · Bell 206B II
Alaska State Troopers Bell 206B II · Accident: airframe, component or system failure while standing
From Willow Airport (UUO) to AK
Event
- NTSB case
- ANC98TA125
- 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
- 0
- 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 206B II
- Aircraft type
- Bell 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
- N70711
- Operator
- Alaska State Troopers
- Onboard fatalities
- Unknown
- Route
- From Willow Airport (UUO), Willow, AKTo AK
- 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
- Standing · idling rotors
- 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
- Airframe, component or system 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
- Miscellaneous rotorcraft, transmission support tube/attchmnt › Fractured
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The commercial helicopter pilot said that he had completed a normal, westerly approach, and subsequent landing atop a 4,000 feet msl mountain. The pilot stated that as he reduced the throttle to the flight idle position, in preparation for engine shut down, a severe airframe vibration occurred. A postaccident inspection revealed that the helicopter's main rotor transmission had been torn from the lower isolation mount assembly, and the helicopter's transmission deck sustained substantial damage. The main rotor drag pin assembly, main rotor driveshaft, forward coupling assembly, and associated fasteners, were sent to the NTSB Materials Laboratory for inspection. The inspection discovered no evidence of a progressive fracture mechanism, and all fracture faces displayed features typical of overstress separation. The main rotor transmission isolation mount was retained by the NTSB, and sent to the manufacture for evaluation, and testing. An FAA airframe certification engineer attended the evaluation process, and reported that the isolation mount operated slightly below acceptable stiffness limits. He added that since the isolation mount sustained damage during the accident, an accurate stiffness value was unattainable.
Probable cause
A fracture of the main rotor drag pin assembly.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ANC98TA125
- Event ID
- 20001211X10756
- Case number
- ANC98TA125
- 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: local date, investigation status. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 1998-08-15.
- API snapshot SHA-256: c631accba3b9c3a18e2d9249d395d13222f07bd4c45af89222bcc5d4450772ce; retrieved 2026-09-22T17:07:34.926Z.