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ASN Wikibase Occurrence # 235262
Last updated: 27 August 2021
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Date:08-JAN-2019
Time:10:00
Type:Silhouette image of generic R44 model; specific model in this crash may look slightly different
Robinson R44 II
Owner/operator:Private
Registration: N484AB
MSN: 11390
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Category:Accident
Location:Uvalde, TX -   United States of America
Phase: Initial climb
Nature:Training
Departure airport:Uvalde, TX (UVA)
Destination airport:Uvalde, TX (UVA)
Investigating agency: NTSB
Narrative:
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.

Sources:

NTSB

Accident investigation:
cover
  
Investigating agency: NTSB
Status: Investigation completed
Duration: 1 year and 3 months
Download report: Final report
Location


Revision history:

Date/timeContributorUpdates
19-Apr-2020 17:28 ASN Update Bot Added

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