Warner Springs, CA, USA
N7117Z
PIPER PA 25-235
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.
HISTORY OF FLIGHTOn September 6, 2014, about 1202 Pacific daylight time, a Piper PA 25-235, N7117Z, collided with terrain while performing glider tow operations at Warner Springs Gliderport, Warner Springs, California. The airplane was registered to, and operated by, Sky Sailing, Inc., under the provisions of 14 Code of Federal Regulations Part 91. The airline transport pilot sustained serious injuries and the airplane was substantially damaged during the accident sequence. The local flight departed Warner Springs about 1200 with a Schweizer SGS 2-33A glider, N7547, in tow. Visual meteorological conditions prevailed, and no flight plan had been filed. On the day of the accident, tailwind departure operations were in effect from runway 26 due to wind conditions and the local topography. The departure procedures required an immediate left turn into the traffic pattern after takeoff, with the landing performed into the wind on the opposing runway. The pilot of the tow plane reported that he had already launched a series of gliders to the area of Mount Palomar without incident, and that his next tow was for N7547. The pilot of the glider indicated via hand signal that he also wanted to fly to Mount Palomar, and the tow was initiated. Quartering left tailwind conditions existed, and the initial ground roll was uneventful. The pair flew in ground effect at a speed of 65 mph, just before reaching the arrival end of runway 8. The tow pilot reported encountering a slight downdraft as he began a left crosswind turn, but stated that this was not unusual for the location. As the turn progressed, he felt the glider slide out of position to the right and above, such that the tow plane was forced into a nose-down attitude. He stated that it was not uncommon for gliders to go out of position at that location, and he was ready to release the glider if the condition worsened. The glider remained out of position as they cleared the trees on the crosswind leg, and by the time they turned downwind the glider began another series of diversions as the tow pilot attempted to continue to climb in the traffic pattern. He reported that they were still low on downwind, but well clear of obstructions. The diversions again became excessive and the tow plane's nose was again forced low. The pitch attitude then recovered, and he could no longer see or feel the glider. The altitude was about 200 feet above ground level (agl), and he assumed that the glider had released. A short time later the tow plane violently yawed to the left and to an extreme nose-low attitude, such that his forward view was now comprised entirely of the ground and trees. The pilot stated that this was the worst deviation he had ever experienced as a tow-pilot, and realizing the glider was still attached, he pulled the line-release handle. He attempted to recover directional control, but the airplane struck the ground nose and right-wing low. The glider pilot stated that shortly after rotation, the nose of the glider pitched up, but he was able to quickly rectify the excursion. During the initial climb the glider continued to climb to a high tow position, and was forced to the right by what he believed was the crosswind. He countered with corrective left rudder input, while also attempting to descend, but he was still far to the right as the tow plane began a left crosswind turn. The tow plane appeared below him and very close to trees as they turned towards downwind, and slack had now developed in the line. He applied corrective right rudder and down-elevator control input and reached for the line handle in anticipation of an early release. He became concerned about his position, but the slack then dissipated with a "jolt." The tow plane then turned left and again slack developed, but this time more severe. The pilot again countered with right rudder and down-elevator input; however, as soon as the line tightened the tow plane began to rock back and forth, and he pulled the release handle. He estimated the altitude at release to be 200 feet agl. He then initiated an uneventful return to land on runway 8. The glider did not sustain any damage, and neither the pilot nor passenger (in the rear seat) were injured. Three witnesses provided corroborating statements of the accident sequence. They reported that the initial takeoff appeared normal until the first crosswind turn when the glider swung out of position to the right and above the tow plane. As the flight progressed to downwind the glider became grossly out of position, with one witness reporting that just prior to release the tow line had formed a "U" shape as the glider gained on the tow plane. The pilot of the glider reported a total flight experience of 1,036 hours in all aircraft, with 56 hours in gliders, 45 of which were in the accident type. He stated that he had flown the downwind departure before, and that he also discussed the procedures with a flight instructor earlier that day. The manager of the gliderport also reviewed his logbooks for currency, and he was cleared to depart.
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.
Source: NTSB Aviation Accident Database
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