LAX04IA135 · Bell 407
Bell 407 · Incident: airframe, component or system failure while maneuvering
From Madera, CA to an unrecorded destination
Event
- NTSB case
- LAX04IA135
- 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
- Incident
- 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 407
- Aircraft type
- Bell 407
- 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
- N601MT
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Madera, CATo 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
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Minor
Cause areas
- Rotor drive system, tail rotor drive shaft bearing › Failure, total
- Rotor drive system, tail rotor drive shaft bearing › Overtemperature
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The pilot executed an autorotative emergency landing following the failure of the number 6 tail rotor drive shaft hangar bearing while maneuvering. The check pilot and pilot were maneuvering the helicopter when it shuddered momentarily, followed by a heavier airframe vibration. The helicopter rolled left as it climbed to 500 feet. The check pilot attempted to turn right towards the airport; however, the helicopter rolled to the left again. The check pilot regained control, shut the engine down, and completed an autorotation to a field. The tail rotor drive shaft coupling was supported by the aft hangar bearing, and inspection revealed that it had sheared in torsional overload due to an overheated and seized number 6 hangar bearing. Post accident examination revealed that the hangar bearing inner race and the balls had large heat affected zones from overheating during operation (the metal in the races ball path had been molten and then had resolidified). The grease was also black and dry, with imbedded metal particles. A series of service bulletins, alert service bulletins, and airworthiness directives (including an emergency AD issued by the FAA) had been issued beginning in October 2001 through 2004 concerning the overheating and failure of the hangar bearings. The bulletins and airworthiness directives dealt with, in part, the modification of the helicopter to include cooling ducts and changes to existing bearings to prevent overheating and eventual bearing failure. The ADs mandated inspections of the hangar bearings every 25 hours of flight; bearing replacement before further flight was called out if metal particles or "black" grease was observed at any bearing.
Probable cause
the failure of the number 6 hangar bearing due to overheating. A factor in the accident was the operator's likely inadequate compliance with service bulletins and airworthiness directives on this issue, along with an inadequate maintenance inspection program for the bearings.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record LAX04IA135
- Event ID
- 20040301X00248
- Case number
- LAX04IA135
- 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, coordinates. 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: 35b5f820420f3d323a5f6969870c6d2d04d5af8101d74554ab5101c83bf5ecac; retrieved 2026-09-22T07:56:12.057Z.