FTW98FA239 · Bell 206L-3
Air Evac EMS Bell 206L-3 · Accident: total loss of engine power (mechanical failure) during initial climb
From an unrecorded airport to Bella Vista, AR
Event
- NTSB case
- FTW98FA239
- 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 206L-3
- 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
- N27AE
- Operator
- Air Evac EMS
- Onboard fatalities
- Unknown
- Route
- From not recordedTo Bella Vista, AR
- 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
- Initial climb
- 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
- Fluid, oil › Flow restricted
- Lubricating system, oil port/passage, internal › Blocked(partial)
- Other maintenance personnel › Maintenance, rebuild/remanufacture, improper
- Turboshaft engine, free turbine shaft › Failure, total
- Turboshaft engine, gas generator turbine shaft › Failure, total
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
Shortly after the helicopter lifted off from a hospital helipad en route to pick up a patient, the engine lost power. The helicopter descended into a parking lot, landed hard, and rolled over coming to rest on its right side. Disassembly of the engine revealed that both the N1 (gas producer turbine) and the N2 (power turbine) shafts had separated. Coke deposits and rub marks were noted on the outside diameter of the N1 shaft. Coke deposits were also present on the inside diameter of the N2 shaft. Metallurgical examination of the shafts determined that coke build up consistent with reduced oil flow led to rubbing between the shafts. The rubbing produced frictional heat that resulted in softening and subsequent failure of the shafts. An o-ring was found lodged in the main oil passage of the accessory gearbox housing. Oil flow testing and calculations showed that this o-ring reduced the oil flow to the turbine shafting from .82 to between .00 and .10 lbs/min. Maintenance records indicated that the engine had accumulated 531 hours since a 3,500 hour gear train inspection, which included disassembly, cleaning, and reassembly of all accessory gearbox components.
Probable cause
The failure of maintenance personnel to properly assemble the engine's accessory gearbox, which resulted in a total loss of engine power due to partial blockage of the main oil passage by an o-ring. The blockage reduced oil flow to the turbine shafting, which led to the total failure of the gas producer turbine shaft and the power (free) turbine shaft. A factor was the lack of suitable terrain for the forced landing.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record FTW98FA239
- Event ID
- 20001211X10054
- Case number
- FTW98FA239
- 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. 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: aa2b42abd153046e304a7df51d0b86c4bca279b1df3f59c707f932cacae90f82; retrieved 2026-09-21T11:31:14.417Z.