WPR17LA113 · Bell 206B B
Paulys Helicopter Services Bell 206B B · Accident: system/component malfunction/failure (non-power) while maneuvering
From Rockville, ID to Rockville, ID
Event
- NTSB case
- WPR17LA113
- 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 206B B
- 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
- N24FS
- Operator
- Paulys Helicopter Services
- Onboard fatalities
- Unknown
- Route
- From Rockville, IDTo Rockville, ID
- Aircraft age
- About 41 years (built 1976)
- 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 137: Agricultural
- 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
- Maneuvering · low-altitude flying
- Defining eventThe 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
- System/component malfunction/failure (non-power)
- 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
- Aircraft › Aircraft propeller/rotor
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The commercial pilot reported that, while conducting an aerial application flight, he performed a 180° turn at an altitude of about 40 to 50 ft above ground level and heard a growling noise, which was followed by the sound of a loud bang and a subsequent loss of power. The pilot lowered the collective, likely to initiate an autorotation to a nearby open field, and the helicopter landed hard.
Postaccident examination of the helicopter airframe and engine revealed that the middle portion of the engine-to-transmission drive shaft was separated between the engine and transmission KAflex couplings. No additional evidence of any preexisting mechanical malfunction was observed.
Metallurgical examination of the shaft and couplings revealed that the shaft had failed from a pair of fatigue cracks at a bolt hole in one element of the flexure coupling (flex frame). This bolt hole exhibited rotational wear severe enough to cause material loss on one face of the bolt hole wall. This circular-wear depression was consistent with repeated rotational contact with an adjacent washer. It is likely that, once the fatigue cracks at the bolt hole propagated deeply enough, the remaining flexure element cross-section fractured from overstress. The failure of this flexure element led to multiple and subsequent overstress failures in other flexure elements, eventually compromising the entire drive shaft assembly.
The circular-wear depression and the longitudinal wear inside the flexure element bolt hole were both consistent with a loose bolt assembly. Because the bolt assembly was loose, the washer would have been able to rub on the flexure element. In addition, the bolt shaft would have been able to rub or gouge the inner wall surfaces of the bolt hole. The bolt and associated washer were not located in the wreckage. None of the maintenance performed on the helicopter about 1 month before the accident involved the flex frame bolt assemblies, so the investigation could not determine how one of the bolts became loose.
Probable cause
The in-flight failure of the engine-to-transmission drive shaft due to a fatigue fracture of one of the KAflex flex frames caused by a loose bolt, which resulted in a total loss of engine power and a subsequent hard landing.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR17LA113
- Event ID
- 20170526X64811
- Case number
- WPR17LA113
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
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. 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: 17c80bcbaf0a8319fa55e65f34347ff4399f06f635f64e82b5f20f969f6da6f7; retrieved 2026-09-16T05:19:33.669Z.