What happened
On October 3, 1998, an ASK-13 glider, registration PH-436, was performing a local training flight at the Axel glider airfield. The flight was part of an instructor-in-training program, with a senior instructor acting as a student and a trainee instructor occupying the rear seat.
During a winch launch, the senior instructor intentionally disconnected the cable at an extremely low altitude—estimated between 15 and 50 meters—to simulate a cable break. Following the trainee's command to adjust the pitch, the senior instructor pushed the control column forward aggressively to transition from a climb to a glide. This sudden maneuver resulted in a high sink rate that could not be arrested before impact. The aircraft struck the runway with a low nose attitude, bounced, and slid approximately 180 meters. The impact caused significant structural damage to the fuselage, tail, and cockpit.
The investigation
The investigation examined the flight dynamics, the roles of the crew, and the technical state of the aircraft. It was established that the ASK-13 was airworthy, and all weight and balance parameters were within limits. The investigation focused on the decision-making process during the simulated emergency.
Investigators noted that the senior instructor was playing a "role" as an inexperienced student, intentionally delaying the necessary pitch adjustment until prompted. This delay, combined with the aggressive corrective action taken at such a low altitude, left insufficient height to stabilize the descent for a normal landing.
Findings
- The primary cause was the execution of a critical maneuver at an extremely low altitude.
- The instructional role-play contributed to the accident, as the senior instructor's intentional delay in responding to the simulated break led to an unrecoverable sink rate.
- The aggressive pitch adjustment required to compensate for the delay resulted in a high descent velocity that could not be mitigated before ground contact.
- The physical impact resulted in one injury (a compressed vertebra for the senior instructor) and substantial damage to the aircraft structure.
Safety action
A recommendation was made to the Royal Dutch Aeronautical Association (KNLTv) regarding instructor training. The safety committee should discuss the risks versus the benefits of simulating cable breaks at low altitudes and review specific aspects of instructor training protocols.