ASN Wikibase Occurrence # 218680
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| Date: | Friday 18 September 2015 |
| Time: | 17:00 |
| Type: |  Robinson R44 |
| Owner/operator: | Bering Pacific Ranches, Ltd. |
| Registration: | N7162R |
| MSN: | 0670 |
| Year of manufacture: | 1999 |
| Total airframe hrs: | 2490 hours |
| Engine model: | Lycoming O-540-F1B5 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Fort Glenn, AK -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Unknown |
| Departure airport: | Fort Glenn, AK |
| Fort Glenn, AK | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The commercial helicopter pilot was conducting an aerial mustering flight with cattle on a remote island. The pilot reported that, while in a hover, he heard “metallic grinding noises” from behind his position in the front right seat; however, the helicopter was “stable with engine power,” the rotor rpm was within normal limitations, and the had “normal responding controls and tail rotor authority.” The pilot immediately landed the helicopter on a sandbar, completed the shutdown process, and exited from the helicopter without further incident. While conducting a postflight inspection, the pilot observed that the tail rotor gearbox had separated from the tailboom mounting assembly and was lying on the ground.
An examination of the tail rotor gearbox mounting flange bolts and the tail rotor blades revealed signatures consistent with overstress. No signatures of pre-existing damage were observed during the examination.
During the low-level profile flown during the aerial mustering operation, it is likely that the tail rotor blades impacted an object which resulted in a severe imbalance of the blades and subsequent separation of the tail rotor gearbox. During the impact and separation sequence, the tail rotor blades likely impacted the vertical stabilizer where the red tail rotor blade “danger” decal is mounted.
An examination of the components could not determine what object was impacted. No evidence of impact with foreign objects such as birds, vegetation, or cattle was observed, although such an impact could not entirely be ruled out since neither of the tail rotor blade tips was recovered.
Probable Cause: The separation of the tail rotor gearbox from the tailboom attachment point due to overstress loads imposed by a tail rotor blade imbalance as the result of impact with an undetermined object during low-level flight operations.
Accident investigation:
 |
|
Sources:
NTSB
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 28-Nov-2018 14:43 | ASN Update Bot | Added |
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