ASN Wikibase Occurrence # 298016
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| Date: | Friday 11 May 2018 |
| Time: | 19:30 LT |
| Type: |  Bell OH-58C |
| Owner/operator: | Tri Rotor Spray |
| Registration: | N82857 |
| MSN: | 41172 |
| Year of manufacture: | 1970 |
| Total airframe hrs: | 7300 hours |
| Engine model: | Allison M250-C20C |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Yuma, Arizona -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Agricultural |
| Departure airport: | Somerton, AZ (PRIV) |
| Somerton, AZ (PRIV) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot of the helicopter was performing an aerial application flight in dark night conditions when he felt a vibration. The pilot pulled back on the cyclic control to stop the helicopter's forward movement and maintained this position for the remainder of the flight. Seconds later, the helicopter had descended to 40 ft above ground level (agl), and the low rotor rpm light indication illuminated, accompanied by multiple other warning lights. The helicopter continued to descend and impacted terrain upright. The main rotor blades severed the tail boom, the left skid dug into the ground, and the helicopter rolled over and came to rest on its right side.
Examination of the helicopter revealed no anomalies with the flight control system. The engine inspection revealed thermal damage to the combustion liner and 1st stage gas turbine producer vanes, consistent with an irregular spray pattern from the fuel nozzle due to carbon buildup. Although the helicopter's weight at the time of the accident exceeded its published maximum gross weight by 100 lbs, whether this contributed to the helicopter's inability to maintain altitude following the loss of engine power was not determined.
The engine logbook indicated that the fuel nozzles were inspected in accordance with the manufacturer's 100-hour inspection checklist about two years before the accident. Although a 100-hour inspection was completed about 4 months before the accident, the maintenance log entry did not specify the work completed, and whether the fuel nozzles were inspected at this time could not be determined; however, the carbon buildup on the fuel nozzles suggested long-term accumulation, and it is likely that maintenance personnel either omitted this inspection item or did not adequately inspect the fuel nozzles. Given the carbon accumulation of the fuel nozzle and signatures of irregular fuel spray, it is likely that the helicopter experienced a partial loss of engine power, which resulted in the subsequent descent into terrain.
Probable Cause: A partial loss of engine power during an aerial application flight due to thermal damage to the 1st stage gas producer turbine nozzle and an irregular fuel spray pattern due to carbon buildup of the fuel nozzle. Contributing to the accident was maintenance personnel's inadequate inspection of the fuel nozzle.
Accident investigation:
 |
|
Sources:
NTSB WPR18LA140
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 15-Oct-2022 11:52 | ASN Update Bot | Added |
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