Piper PA 25-235 N7117Z accident near Warner Springs, California

Probable cause

The glider pilot's failure to maintain directional control during the initial climb while being towed, which led to the tow plane's unstable flight and its subsequent aerodynamic stall. Contributing to the accident was the tow pilot's delayed release of the glider.

NTSB analysis

The pilot of the tow plane had already launched a series of gliders without incident just before the accident. Downwind departure operations were in effect due to wind conditions and the local topography; the glider pilot had been briefed on the departure procedures earlier in the day and had experience flying the departure. For the accident flight, the glider was moved into position, and the glider pilot indicated his intentions via hand signals.

Shortly after takeoff, the glider moved out of position. The glider pilot made corrective control inputs as the flight progressed in the traffic pattern; however, he was unable to establish positive control. The glider violently yanked and pulled the tow plane into unusual attitudes throughout the departure, and a positive rate of climb could not be established. The glider pilot continued to encounter control difficulties consistent with pilot-induced oscillations, and the tow line became slack as the glider gained on the tow plane. The tow plane pilot thought the glider had released, and a few seconds later, as the line went taught, the tow plane was forced into an aerodynamic stall. Both pilots simultaneously released the tow line, and, with minimal altitude remaining for recovery, the tow plane crashed in a field just beyond the runway. The glider returned to the airport and landed without incident.

Text from the NTSB. Open the NTSB docket for WPR14LA367 for the full record.