What happened
On June 28, 2003, a Schempp Standard Austria SH glider, registration PH-1069, departed from Woensdrecht Air Base for a local flight. The pilot, an experienced aviator with over 1,400 hours of glider flight time, was flying this specific aircraft type for the first time. Approximately fifteen minutes into the flight, witnesses south of the air base observed the aircraft undergoing significant altitude changes, characterized by a sharp descent followed by a steep climb while the fuselage remained nearly horizontal.
As the pilot initiated a sharp left turn, the aircraft's left wing dropped, leading into a semi-spin. Although witnesses noted an attempt to recover the aircraft after two full rotations, the maneuver failed. The glider crashed into a field, resulting in one fatality.
The investigation
The investigation focused on the aircraft's flight characteristics and the environmental conditions at the time of the accident. The aircraft featured a V-tail configuration, which combines elevator and rudder functions. While the owner had briefed the pilot on the cockpit layout, takeoff procedures, and the unique handling characteristics of the V-tail, the investigation looked into whether these characteristics contributed to the loss of control.
Technical inspections of the wreckage revealed no mechanical failures. The total mass of the PH-1069 was approximately 8 kg (2.3%) above the maximum allowable weight, but this margin was considered too negligible to be a contributing factor. The center of gravity was found to be within the standard limits, meaning the pilot's position would not have required specialized recovery procedures.
Findings
- The investigation identified that the pilot likely encountered strong localized thermic activity or unexpected air currents. A sudden transition from a downdraft to a strong updraft may have increased the wing's angle of attack significantly.
- During the subsequent turn, this increased angle of attack likely led to an aerodynamic stall.
- The V-tail design presents a specific challenge: the maximum rudder deflection is limited when full elevator is applied, and vice versa. Furthermore, in a spin, one part of the V-tail can enter the fuselage's wake, reducing rudder effectiveness.
- The pilot's attempt to recover the aircraft was likely hindered by the high angle of attack and the specific aerodynamic limitations of the V-tail during a stall-induced spin.
Safety action
No specific safety recommendations were issued as no mechanical or procedural failures were identified as the primary cause.