Flight control systems involving a Schempp-Hirth Flugzeugbau GmbH Cirrus 75, VH-XQZ, Central Mangrove, New South Wales, on 7 October 1995

The glider was nearing the end of a 190 km cross country flight. The weather was fine, with good visibility and light west to north westerly winds. At about five km from the airfield the pilot decided to descend from 3,500 ft by increasing airspeed to 116 kt, some 3 kt less than the maximum airspeed limit.

The pilot reported that initially the glider was flying normally at this speed, but suddenly the control stick was pulled from his grasp and vibrated back and forth, banging against its stops. He managed to regain his hold on the stick and began to raise the nose of the aircraft to reduce airspeed. At this point the glider rolled into an inverted attitude.

Believing that the aircraft had suffered a major structural failure, the pilot elected to escape from the cockpit and make a parachute descent. Initially, he experienced difficulty in releasing the canopy, but once open he fell freely from the glider. The pilot made a successful parachute descent, whilst the glider proceeded to land in bushes, sustaining minimal damage.

During a subsequent airworthiness inspection by the gliding authority, it was found that the mass balance of the tailplane was beyond limits. The out of balance condition had apparently occurred some three years previously when the glider had been rebuilt. As a result, elevator flutter had occurred as the aircraft reached its maximum airspeed limit. Under normal circumstances the critical airspeed for the onset of elevator flutter should have been well in excess of the maximum airspeed limit. 

The gliding authority has advised that it has taken action to prevent a recurrence by issuing an airworthiness directive, and conducting surveillance of the maintenance organisation concerned.