What happened
During a glider tow operation, the pilot of the glider failed to verify that the aircraft's spoilers were retracted and in the locked position prior to takeoff. During the initial climb phase, the pilot of the towplane radioed a warning regarding the spoilers. A witness confirmed that the spoilers were indeed extended.
As the glider pilot attempted to retract the spoilers, the glider entered a nose-high, pitch-up attitude. The glider pilot realized the aircraft was in a high tow position; however, before the pilot could manually release the tow line, the tow rope broke due to overload. Although the break occurred within the specified tensile limits required by regulations, the loss of tension caused the towplane to climb to approximately 150 feet AGL before pitching nose down. The towplane descended in an approximate 45-degree flight path, resulting in a wings-level ground impact. At the time of impact, the aircraft was 40-50 degrees nose low, and the engine was developing power.
The investigation
Investigators examined the aircraft's tow hook release latch mechanism. The examination revealed that there was a potential for the release latch to bind when the towed aircraft moved significantly above the horizontal (trail) position.