FTW01LA087 · Bell 47G2
Versatile Helicopters Bell 47G2 · Accident: rotor failure/malfunction while maneuvering
From Ardmore Downtown Executive Airport (1F0) to 1F0
Event
- NTSB case
- FTW01LA087
- 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 47G2
- 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
- N1575
- Operator
- Versatile Helicopters
- Onboard fatalities
- Unknown
- Route
- From Ardmore Downtown Executive Airport (1F0), Ardmore, OKTo 1F0
- 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
- Rotor failure/malfunction
- 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
- Lubricant, grease › Leak
- Pilot in command(cfi) › Tail rotor/anti-torque control, not possible
- Rotor drive system, tail rotor drive shaft coupling › Loose part/bolt/nut/clamp/etc
- Rotor drive system, tail rotor drive shaft coupling › Stripped thread
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
During a night flight, the helicopter was in level flight, about 1,400 feet MSL over a lake as the student pilot commenced a turn to the left with a forward airspeed of about 45 to 50 knots. The CFI then "came onto the controls" to assist with the coordinated turn, and noticed that the cockpit turn indicator showed that the helicopter was "slipping." Subsequently, the CFI applied left pedal to correct, and as soon as the left pedal was applied, the airframe shuddered and started to yaw to the right. The airspeed started to decrease and the helicopter began to "spin to the right rapidly." The CFI then applied full left pedal and the helicopter continued to spin to the right. After lowering the collective and reducing the throttle, the helicopter stopped spinning. The CFI then lowered the nose and maneuvered the helicopter toward shallow water near the heavily vegetated shoreline, flaring and pulling up on the collective to cushion the landing. The helicopter came to rest on its left side in the shallow water. Examination of the helicopter revealed that the splined coupling at the aft end of the forward tail rotor drive shaft segment was damaged. Removal of the dust cover for the coupling revealed that the screw and washer, part numbers AN501A10-4 and AN960-10, were loose with several of the threads stripped, thus allowing grease to weep during operation. The forward tail rotor drive shaft assembly, part number 47-644-18-9, was replaced on January 29, 2001. The helicopter had accumulated 70 hours of flight time since the last 100- hour inspection and 23 hours since the last 50- hour lubrication.
Probable cause
the loss of tail rotor control during maneuvering resultant from the failure of the tail rotor drive shaft coupling due to a stripped thread which allowed the grease lubricating the shaft to leak out. A factor was the lack of suitable terrain for the forced landing (autorotation).
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record FTW01LA087
- Event ID
- 20010327X00653
- Case number
- FTW01LA087
- 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 2001-03-22.
- API snapshot SHA-256: 425c9474b16439781bcf8f3ffb3a8492480ab53d452cb8a18ee36c2998249548; retrieved 2026-09-22T12:05:16.403Z.