Accident MBB BK117 C-1 N911RR,
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ASN Wikibase Occurrence # 284398
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Date:Monday 20 August 2007
Time:08:30 LT
Type:Silhouette image of generic BK17 model; specific model in this crash may look slightly different    
MBB BK117 C-1
Registration: N911RR
MSN: 7502
Year of manufacture:1992
Fatalities:Fatalities: 0 / Occupants: 2
Aircraft damage: Substantial
Location:Slaton, Texas -   United States of America
Phase: Unknown
Departure airport:SLATON, TX (F49)
Destination airport:Lubbock Preston Smith International Airport, TX (LBB/KLBB)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The helicopter drifted backwards during a confined area operations training and the tail rotor blades struck tree branches while hovering over tall grass. The 11,330 hour flight instructor and the 16,800 hour pilot receiving instruction reported that they were both familiar with the training area being used, the flight was properly briefed, and they had both worked together as a crew in the past. The crew reported that the pilot performed a high recon of the landing area, noting the surface winds, approach and departure paths, and the conditions of the landing zone. The approach was planned to terminate at a hover. The grass at the landing zone is normally less than a foot long; however, due to the record rainfall this year, the grass was 3-to-4 feet tall. Both pilots underestimated the effects of prolonged hovering over tall grass. The tall-waving grass disoriented the pilot and allowed the helicopter to drift into the trees. The flight instructor was clearing the left side of the helicopter during the approach and hover, but was unable to react in time to take the flight controls to stop the drift. The flight crew immediately landed the helicopter in the confined area when they felt a vibration from the tail rotor. The helicopter was recovered to the operator's maintenance facility for damage assessment. Examination of the helicopter by the flight crew, the operator, and the FAA inspector, confirmed that both tail rotor blades were destroyed, the mounting bolts for the tail rotor 90 degree box were damaged or broken, and the tail fin gearbox mounting spar was also damaged.

Probable Cause: The pilot's failure to maintain control of the hovering helicopter and the flight instructor's improper supervision of the flight.

Accident investigation:
Investigating agency: NTSB
Report number: DFW07CA186
Status: Investigation completed
Duration: 2 months
Download report: Final report



Revision history:

30-Sep-2022 16:06 ASN Update Bot Added

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