What happened
On June 16, 2014, at approximately 12:15 local time, a Grob G 103 C “TWIN III ACRO” glider was performing a training flight via winch launch from the Erbach airfield. Shortly after the aircraft lifted off, witnesses observed a significant decrease in the tension of the winch cable. This loss of tension caused the cable to sag heavily, triggering the automatic release mechanism of the glider's release hook at an altitude of approximately 30 meters.
The flight instructor noted the drop in cable tension and responded by reducing the aircraft's climb angle. Following the loss of winch assistance, the glider descended and struck the runway with significant force. The impact caused the fuselage tube to break approximately 15 cm before the tail unit, and damage was also sustained to the rudder and elevator.
The investigation
The BFU investigation examined the sequence of events, the aircraft's condition, and the environmental factors at the time of the accident. The investigation confirmed that the accident occurred roughly 270 meters from the start point of the winch launch path. The aircraft, a composite construction model, had been in service since 2007 and had undergone its last airworthiness inspection in April 2014. Meteorological data indicated excellent visual flight rules (VFR) conditions with clear visibility and light winds.
Findings
- The primary cause of the accident was the significant loss of winch cable tension immediately after takeoff.
- The reduction in tension led to a heavy sag in the cable, which caused the automatic release mechanism to disengage.
- The resulting loss of climb capability forced a hard landing on the runway, leading to two serious spinal injuries for the occupants and heavy damage to the aircraft.