What happened
On the morning of July 26, 1998, a Schleicher ASK 23 B glider, registration PH-765, was prepared for its first flight of the day at Hilversum Airport. Due to a local market being held near runway 13, the airport service had relocated glider operations to runway 18, moving the winch position to the south side of the field.
Following a successful winch launch, the pilot began a circuit flight. However, during the maneuver, the pilot became disoriented regarding which runway and circuit were currently active. Based on the perceived location of the winch, the pilot incorrectly concluded that runway 1 and 25 were not in use and that only runway 13 remained valid for a left-hand circuit.
In an attempt to correct the flight path, the pilot flew past the landing point on the runway 18 circuit and executed a 180-degree turn. This maneuver took the aircraft across the final approach path of runway 18 twice. The pilot continued toward Loosdrecht at a very low altitude, eventually turning back toward the airfield. During this low-altitude turn, the aircraft struck the treetops at the edge of the field and struck the ground with high vertical velocity.
The investigation
The investigation examined the pilot's preparation and the operational changes at the airfield. It was noted that the pilot was accustomed to flying on Wednesdays when powered aircraft towing was standard, rather than the Sunday winch-launching setup experienced that day. The investigation found that the pilot had bypassed thorough pre-flight preparations because the instructor had signaled that the aircraft was ready for immediate takeoff.
Investigators also looked into the airfield's layout, noting that the grass runways at Hilversum lack high contrast with the surrounding environment. The pilot's confusion was linked to the unusual position of the winch, which the pilot mistakenly associated with previous evening visits to the field when the runway configuration was different.
Findings
- The pilot suffered a broken spinal vertebra and other injuries, while the Schleicher ASK 23 B sustained heavy damage to the fuselage and wingtip.
- The pilot's lack of adequate preparation for the specific day's operational changes led to disorientation.
- The pilot's incorrect assumption regarding the winch position caused a miscalculation of the active runway and circuit.
- The accident became unavoidable once the pilot attempted to turn back to the field at an altitude too low to clear the surrounding trees.