ASN Wikibase Occurrence # 385631
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| Date: | Tuesday 10 July 2001 |
| Time: | 06:30 LT |
| Type: |  Bell 206B |
| Owner/operator: | Raco Helicopters |
| Registration: | N3298G |
| MSN: | 1909 |
| Year of manufacture: | 1976 |
| Total airframe hrs: | 2023 hours |
| Engine model: | Rolls-Royce 250 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Secaucus, NJ -
 United States of America
|
| Phase: | En route |
| Nature: | Agricultural |
| Departure airport: | Jersey City, NJ (NONE) |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot had just completed a spraying pass, and was heading westbound about 100 feet and 60 mph, parallel to power lines and 15-20 feet above trees. He suddenly felt something "break", and the helicopter started to yaw. The pilot realized that the helicopter had experienced a tail rotor failure, but he didn't want to autorotate into trees. He reduced the throttle slightly, maintained altitude, spun around two to three times, and cleared the trees. He headed for a gravel area and rolled off the throttle, but couldn't stop the spin. He attempted to cushion the landing, but the helicopter hit the ground hard. On-scene examination revealed that the Thomas coupling disc assembly on the aft end of the aft short shaft was twisted and bent, and the tail rotor drive shaft just aft of the coupling was bent and separated, about mid-length. A retaining bolt was missing from the Thomas coupling. The missing bolt and washers were found in the helicopter's tailrotor drive shaft tunnel area, and appeared to be undamaged. The self locking retaining nut for the bolt was not located. Metallurgical review revealed that the Thomas coupling at the aft end of the aft short shaft was missing one of the bolt and nut sets that attached the coupling to the splined adapter at the forward end of the first segment of the tail rotor drive shaft. The forward face of the flange adapter contained a series of rotational scoring and impact marks from contact with the bolt heads and discs. The pattern of damage was consistent with the short shaft rotating around the bolt opposite from the missing bolt. Additional examination of the Thomas coupling and associated components revealed that portions of the normal seating positions for the head of the missing bolt and the washer were relatively free of dirt and grease, and that the bore surface of the hole for the missing bolt in the flanged adapter at the forward end of the first segment contained thread imprint marks.
Probable Cause: Under torque of a Thomas coupling self-locking nut for undetermined reasons, which resulted in the loss of the corresponding retaining bolt, and subsequent separation of tail rotor drive shaft segments. A factor was the unsuitable terrain beneath the pilot when the loss of tail rotor occurred.
Accident investigation:
 |
|
Sources:
NTSB NYC01LA168
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 05-Apr-2024 06:12 | ASN Update Bot | Added |
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