Loss of control Accident Robinson R44 II N484AB,
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ASN Wikibase Occurrence # 235262
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Date:Tuesday 8 January 2019
Type:Silhouette image of generic R44 model; specific model in this crash may look slightly different    
Robinson R44 II
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
Location:Uvalde, TX -   United States of America
Phase: Initial climb
Departure airport:Uvalde, TX (UVA)
Destination airport: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:
Investigating agency: NTSB
Report number: CEN19LA065
Status: Investigation completed
Duration: 1 year and 3 months
Download report: Final report




Revision history:

19-Apr-2020 17:28 ASN Update Bot Added

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