ASN Wikibase Occurrence # 227680
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| Date: | Saturday 27 July 2019 |
| Time: | 16:28 LT |
| Type: |  Robinson R44 Raven II |
| Owner/operator: | NE IA Helicopters LLC |
| Registration: | N7508Z |
| MSN: | 10609 |
| Year of manufacture: | 2005 |
| Total airframe hrs: | 2350 hours |
| Engine model: | Lycoming IO-540-AE1A5 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | W of Blair Municipal Airport, Washington County, NE -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Agricultural |
| Departure airport: | Blair, NE |
| Blair, NE | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
After completing a spray pass during a helicopter aerial application flight, the pilot initiated a climb over trees to head south. The pilot reported that, at the top of the climb, he noticed that the engine rpm was beyond "max limitations" and that the main rotor rpm was in the green range. The pilot initiated a right pedal turn to the north and decreased the engine throttle to lower the engine rpm. The engine rpm remained at the upper limit, but the main rotor rpm decreased. The pilot then attempted to correct the main rotor rpm by increasing the throttle; however, the main rotor rpm fluctuated and then continued to decrease. Unable to control and maintain the main rotor rpm, the pilot performed a forced landing to a field with sloped terrain, during which the main rotor blades impacted terrain. The helicopter sustained substantial damage to the main rotor blades and tailboom.
Postaccident examination of the upper and lower actuator support bearing brackets revealed they were separated from the scroll, and evidence of fretting and rub marks was noted between the brackets and scroll walls. In addition, elongated rivet holes were observed on the scroll wall, and the associated rivets were sheared. Torque paint was noted on the outboard rivets.
It is likely that the bracket supporting the lower actuator bearing became loose and sheared the rivets, which allowed the actuator bearing to shift and led to a subsequent misalignment of the clutch actuator. The misalignment of the clutch actuator resulted in the loss of belt tension between the engine and main rotor drive system. The reason for the loose bracket and sheared rivets could not be determined due to damage.
A manufacturer service bulletin required an inspection of the brackets for evidence of fretting or looseness, and that was accomplished about 169 flight hours before the accident. The compliance procedure, which was to occur at the next 100-hour or annual inspection, was to visually inspect the brackets and attaching rivets for evidence of fretting or looseness and, on the lower bracket, to apply torque seal in a vertical stripe across both outboard rivets to lower scroll to facilitate future inspections. It is likely that the wear was not apparent at the time of the inspection.
Probable Cause: The failure of the lower actuator bearing support bracket, which resulted in the misalignment of the clutch actuator, the loss of belt tension on the main rotor drive system, and the subsequent forced landing on sloped terrain.
Accident investigation:
 |
|
Sources:
https://flightaware.com/resources/registration/N7508Z
NTSB CEN19LA240
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 27-Jul-2019 23:39 | Captain Adam | Added |
| 29-Jul-2019 20:30 | Geno | Updated [Time, Aircraft type, Registration, Cn, Operator, Source] |
| 27-Mar-2021 09:50 | ASN Update Bot | Updated [Time, Other fatalities, Departure airport, Destination airport, Source, Narrative, Category, Accident report] |
| 27-Mar-2021 10:38 | harro | Updated [Source, Narrative] |
Corrections or additions? ... Edit this accident description
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