FTW95LA239 · Bell 47G-5
Bell 47G-5 · Accident: airframe, component or system failure while maneuvering
Event
- NTSB case
- FTW95LA239
- 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 47G-5
- Aircraft type
- Bell 47
- 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
- N1502L
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From not recordedTo not recorded
- 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
- Maneuvering
- 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
- Also codedOther events the NTSB coded in the sequence, such as a wire strike after a loss of power. Flight Findings uses them for its kinds of event. Glossary
- Tree(s)
- 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
- Maintenance, installation › Inadvertent use
- Material inadequate
- Rotor drive system › Disconnected
- Rotor drive system, tail rotor drive shaft bearing › Failure, total
- Rotor drive system, tail rotor drive shaft coupling › Unapproved part
- Rotor drive system, tail rotor drive shaft coupling › Worn
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
AS THE HELICOPTER WAS BEING MANEUVERED AT LOW ALTITUDE TO HERD CATTLE, THE TAILROTOR DRIVE LOST CONTINUITY. THE PILOT REPORTED THAT DIRECTIONAL CONTROL WAS LOST, AND THAT HE EXECUTED AN AUTOROTATION INTO A CONFINED AREA. DURING DESCENT/LANDING, THE MAIN ROTOR BLADE STRUCK A TREE, AND THE HELICOPTER ROLLED ONTO ITS RIGHT SIDE. AN INVESTIGATION REVEALED EXCESSIVE WEAR ON THE TAIL ROTOR GEAR/DRIVE ASSEMBLY (TRANSMISSION OUTPUT QUILL GEAR). A METALLURGICAL EXAMINATION OF THE ASSEMBLY REVEALED THAT THE GEAR'S SHAFT (WHICH CONSTITUTED THE INNER RACEWAY OF AN ASSOCIATED CYLINDRICAL BEARING) HAD NOT BEEN CARBURIZED AS REQUIRED BY THE DESIGN MANUFACTURER. ROTATION OF THE BEARING ROLLERS OVER THE RELATIVELY SOFT SURFACE OF THE SHAFT HAD WORN A GROOVE IN THE SHAFT. THE ASSOCIATED BEARING (TAIL ROTOR DRIVE ASSEMBLY BEARING) SUBSEQUENTLY FAILED. THE GEAR AND BEARING WERE UNAPPROVED PARTS AND DID NOT CONFORM TO THE MANUFACTURER'S DESIGN SPECIFICATIONS. THE SOURCE OF THE UNAPPROVED PARTS WAS NOT DETERMINED, ALTHOUGH PACKAGING OF THE PARTS WAS REPORTED TO RESEMBLE THAT OF THE MANUFACTURER. PART NUMBERS WERE FOUND ON THE GEAR AND BEARING, SIMILAR TO AUTHORIZED PARTS, ALTHOUGH A DIFFERENT METHOD OF MARKING (ETCHING) WAS USED TO MARK THE GEAR.
Probable cause
INADVERTENT INSTALLATION OF AN UNAPPROVED PART (TAIL ROTOR GEAR/DRIVE ASSEMBLY), THAT BECAME EXCESSIVELY WORN SINCE IT DID NOT CONFORM TO THE MANUFACTURER'S SPECIFICATION, RESULTING IN FAILURE OF THE ASSOCIATED TAIL ROTOR BEARING (ALSO AN UNAPPROVED PART), LOSS OF CONTINUITY (DISCONNECT) OF THE TAIL ROTOR DRIVE SYSTEM, AND A FORCED AUTOROTATION INTO AN AREA WITH TREES.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record FTW95LA239
- Event ID
- 20001207X03476
- Case number
- FTW95LA239
- 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: 61cabbfbe3e4379d8509833e6a799860b1870ed06ef45dd468759845dd226f1d; retrieved 2026-09-22T23:54:07.304Z.