ASN Wikibase Occurrence # 292381
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| Date: | Thursday 4 May 2006 |
| Time: | 08:30 LT |
| Type: |  Bell 206B3 |
| Owner/operator: | Pacific Rotors, Inc. |
| Registration: | N2763R |
| MSN: | 2743 |
| Year of manufacture: | 1979 |
| Total airframe hrs: | 15437 hours |
| Engine model: | Allison 250-C20B |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Fallbrook, California -
 United States of America
|
| Phase: | Unknown |
| Nature: | Agricultural |
| Departure airport: | Fallbrook, CA |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The helicopter collided with trees following a failure of the engine to transmission drive shaft. After finishing a final rinse load for the agricultural spray operation, the pilots began the short return flight back to a trailer. While maneuvering about 20 feet above ground level (agl), and about 5 feet above the treetops, the helicopter made an uncommanded yaw and settled into the trees. A post accident examination revealed that the engine to transmission drive shaft (short shaft) was separated at the forward coupling flange, adjacent to the transmission. Investigators removed the rust-covered engine to transmission drive shaft forward coupling from the gear. The retainer ring, packing seal, and drive shaft coupling seal were not attached to the coupling and dangling loosely on the drive shaft tube. A visual examination of the internal coupling revealed that grease retainer plate had a shiny polished appearance from the gear sprocket making repetitive contact with its surface. The engine to transmission drive shaft forward gear sprocket teeth were not present, as a result of overheating and persistent contact, which had worn them smooth. On the face of the gear sprocket there was a semicircular indentation that had the shape and dimension consistent with that of a partial impression of the spring that is normally inside the coupling. Pieces of the spring were found deformed in the aft coupling housing. There was no evidence of grease in the forward coupling, and the aft coupling contained grease that was dirty and black. The operator's component card record for the engine to transmission drive shaft indicated that it was last inspected about 2 months prior to the accident at which time a mechanic repacked the couplings with grease. The helicopter's applicable Maintenance Manual indicated that every 600-hour or 12-month period (whichever occurs first) the main drive shaft component should be inspected.
Probable Cause: Failure of the engine to transmission drive shaft forward coupling due to overheating from lack of lubrication. The cause of the lack of lubrication was a result of improper maintenance. A factor was the trees.
Accident investigation:
 |
|
Sources:
NTSB LAX06LA161
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 08-Oct-2022 18:02 | ASN Update Bot | Added |
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