Bell OH-58A N337PW accident near Pine Springs, Texas

Probable cause

The pilot's failure to maintain directional control while operating in conditions conducive to a loss of tail rotor effectiveness.

NTSB analysis

The pilot and two passengers were surveying a preplanned transect about 50 to 100 feet above ground level with a 5- to 10-knot left crosswind and an indicated groundspeed of 30 to 35 knots. As the terrain began to rise, the pilot added power to clear a ridge. The pilot reported that, when the helicopter was about 100 feet from the top of the ridge, he heard a " slight pop" and that the helicopter began to yaw to the right. He added power to clear the ridgeline, which greatly increased the right yawing motion, and the helicopter began to spin. He stated that the helicopter crossed over the ridgeline backward and continued to spin before it contacted the ground and rolled over onto its left side. A passenger reported that, although the wind was about 10 knots when they started the survey, the wind speed increased when the helicopter reached the top of the ridge, and the pilot had to correct for it twice before the helicopter began to spin to the right. A postaccident examination of the helicopter revealed no preimpact mechanical malfunctions or failures that would have precluded normal operation. The helicopter was operating in an environment conducive to the loss of tail rotor effectiveness (LTE), and the unanticipated right yaw and subsequent spinning of the helicopter are consistent with LTE.

Text from the NTSB. Open the NTSB docket for CEN13TA165 for the full record.