ASN Wikibase Occurrence # 286483
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| Date: | Saturday 10 October 2009 |
| Time: | 19:45 LT |
| Type: |  Bell OH-58A |
| Owner/operator: | |
| Registration: | N911AF |
| MSN: | 41626 |
| Year of manufacture: | 1971 |
| Total airframe hrs: | 8043 hours |
| Engine model: | Rolls Royce 250 C20C |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Ocala, Florida -
 United States of America
|
| Phase: | Approach |
| Nature: | Unknown |
| Departure airport: | Ocala-Taylor Field, FL (OCF/KOCF) |
| Ocala-Taylor Field, FL (OCF/KOCF) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot stated that while on final approach for landing, at about 20 knots and 120 feet above ground level, he felt a "vibration" and the helicopter experienced a loss of engine and rotor rpm. The pilot stated that he lowered the collective for an immediate landing and heard the low-rotor warning horn during the descent. The helicopter experienced a hard landing and rotated to the left after touchdown. Once the helicopter settled, the pilot closed the throttle and exited the helicopter. Initial examination of the helicopter revealed no preimpact mechanical anomalies. The engine was then removed from the helicopter and the turbine governor was removed from the engine. As the turbine governor was removed from the engine, several rolling elements (balls) spilled from the governor and were not recovered. Disassembled portions of the governor were forwarded to the NTSB Materials laboratory and examination of the components revealed the lubricant used was consistent with what was prescribed by the manufacturer. Further examination revealed displacement of the governor driveshaft, deformation of a bearing seal, rotational damage on bearing lands and spacers, as well as spalling on rolling components of the governor. The damage was consistent with wear over an extended period, and neither the cause nor the sequence of wear and failure of the examined components could be determined. Examination of maintenance records revealed that the governor was in service 30 hours beyond its 2,000-hour time-before-overhaul (TBO) interval, but that under the military maintenance program by which the helicopter was maintained, TBO intervals could be adjusted plus or minus 75 hours to align with other scheduled maintenance. Examination of the manufacturer's Operator's Manual revealed that the loss of engine power occurred at an altitude that fell in the "avoid area" of the Height Velocity diagram. According to the manual, 'Flight conducted within the avoid area of the chart (figure 9-3) exposes the helicopter to a high probability of damage despite the best efforts of the pilot."
Probable Cause: The excessive wear and failure of engine governor components for undetermined reasons, which resulted in a loss of engine power.
Accident investigation:
 |
|
Sources:
NTSB ERA10GA015
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 03-Oct-2022 11:28 | ASN Update Bot | Added |
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