ASN Wikibase Occurrence # 235262
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| Date: | Tuesday 8 January 2019 |
| Time: | 10:00 |
| Type: |  Robinson R44 II |
| Owner/operator: | Private |
| Registration: | N484AB |
| MSN: | 11390 |
| Year of manufacture: | 2006 |
| Total airframe hrs: | 1680 hours |
| Engine model: | Lycoming IO-540-AE1A5 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Uvalde, TX -
 United States of America
|
| Phase: | Initial climb |
| Nature: | Training |
| Departure airport: | Uvalde, TX (UVA) |
| Uvalde, TX (UVA) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The student pilot and flight instructor were conducting a local, instructional flight. The instructor reported that, as the student was transitioning the helicopter through effective translational lift about 40 knots airspeed, he raised the collective to increase the available power to the takeoff power setting. Shortly thereafter, he heard a loud "pop/bang sound," which was followed by an uncommanded right yaw and severe vibrations. Due to the low altitude and airspeed, the instructor immediately took the flight controls and initiated an autorotation. Upon touchdown, the helicopter tilted forward, and the instructor applied aft cyclic to correct; however, the main rotor blades contacted the tailboom, which resulted in the tailboom partially separating from the helicopter.
During postaccident examination of the helicopter, the clutch assembly lubricant was drained, and metallic debris was found in the strainer. Disassembly of the clutch assembly revealed galling of the sprags and the corresponding sprag contact surfaces on the clutch shaft and hub. It is likely that the excessive galling resulted in the sprag clutch slipping, which produced the uncommanded right yaw and led to the student's and instructor's inability to maintain helicopter control.
Probable Cause: The slipping of the sprag clutch due to galling of the sprags and corresponding sprag contact surfaces within the clutch assembly, which rendered the helicopter uncontrollable.
Accident investigation:
 |
|
Sources:
NTSB
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 19-Apr-2020 17:28 | ASN Update Bot | Added |
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