ASN Wikibase Occurrence # 30435
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| Date: | Tuesday 24 August 1999 |
| Time: | 23:00 LT |
| Type: |  Bell UH-1B |
| Owner/operator: | San Joaquin Helicopters |
| Registration: | N999SJ |
| MSN: | 1025 |
| Year of manufacture: | 1963 |
| Total airframe hrs: | 7856 hours |
| Engine model: | Lycoming T53-L11B |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | near Delano, CA -
 United States of America
|
| Phase: | Initial climb |
| Nature: | Agricultural |
| Departure airport: | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
During the takeoff initial climb as the helicopter accelerated through 25 to 30 miles per hour, the 90-degree gearbox fractured through the center of the gearbox case and separated from the tailboom. The pilot was able to slow the spin rate and performed a hovering autorotation. A portion of the tail boom impacted a barbed wire fence as the helicopter settled vertically. Metallurgical examination of the gearbox case fractures disclosed overload features. Internal examination of the gearbox and gears showed that the pinion and gear teeth had disengaged. The disengagement lasted a short period of time. As a result of the disengaged gear and pinion rotating against each other, the gearbox case became overloaded and subsequently separated. The wear patterns on the pinion and gear teeth drive side did not meet the patterns specified in the maintenance manual; the patterns extended off the toe ends and the tips of the teeth. The gearbox, which is an 'on-condition' component, was last overhauled or repaired in 1984. There is no requirement for an internal inspection of the tail rotor gearbox during routine or annual maintenance inspections.
Probable Cause: Failure and separation of the 90-degree gearbox as a result of the disengagement of the pinion and gear teeth. The cause(s) of the pinion and gear disengagement were undetermined.
Accident investigation:
 |
|
Sources:
NTSB LAX99LA283
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 27-Sep-2008 01:00 | ASN archive | Added |
| 23-Oct-2017 16:41 | TB | Updated [Total fatalities, Total occupants, Other fatalities, Location, Country, Phase, Nature, Source, Damage, Narrative] |
| 14-Dec-2017 08:46 | ASN Update Bot | Updated [Time, Operator, Source, Narrative] |
| 07-Apr-2024 18:31 | ASN Update Bot | Updated [Time, Other fatalities, Source, Narrative, Category, Accident report] |
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