What happened
On 14 September 2001, a Piper PA-25-235 Pawnee, registration G-ASLK, was performing aerotow operations at Aston Down Airfield. Due to a winch failure earlier that morning, the aircraft had been ferried from Nympsfield to assist the local gliding club. During the afternoon, the pilot had completed several successful launches.
As the aircraft returned to the airfield, the tug was executing a left-hand base leg, intending to cross the extended centerline of Runway 03 and land diagonally across the southern grass area. Simultaneously, a Cirrus glider was performing a right-hand circuit for a landing on the same grass area.
At an altitude estimated between 150 and 400 feet, the two aircraft converged. The glider was in a slight right bank, while the tug was in a 20-degree left bank. Neither pilot took evasive action before the aircraft collided. The impact caused the glider's left wing tip and aileron to separate and the tug's propeller to strike the glider's tailplane. Both aircraft entered uncontrolled descents, and both pilots were fatally injured upon impact with the ground.
The investigation
Investigators examined the wreckage of both aircraft, which lay in ploughed fields approximately 160m apart. The investigation established that the tug's left wing struts had suffered heavy damage from the collision, leading to a structural failure where the left wing folded upward. This caused the tug to enter a steep, spiralling dive.
On the glider, the investigation found distinct chordwise cuts on the left tailplane, consistent with strikes from the tug's propeller. The glider's left wing tip had also been cleaved by the collision. Analysis of the flight paths using 3D computer models revealed that while neither aircraft was physically obscured by the other's structure, the opposing aircraft presented a very small profile. If either pilot was focused on the landing area rather than scanning the periphery, the other aircraft would have been difficult to detect.
Findings
- The tug aircraft's flight path crossed the final approach path of the glider.
- The collision was caused by the convergence of the two aircraft on opposing tracks while approaching a common landing area.
- The impact caused significant structural damage to both aircraft, including the failure of the tug's left wing struts and the loss of the glider's left wing tip and tailplane sections.
- The small visual profile of the converging aircraft made them difficult to identify in the peripheral field of vision if the pilots were concentrating on the landing zone.
Safety action
- The BGA was recommended to advise gliding clubs to review procedures to ensure separation between powered aircraft and gliders and to improve the use of external lighting on tugs.
- A recommendation was made to review radio procedures to improve situational awareness during glider operations.
- It was recommended that the BGA oversee a standard core syllabus for tug pilot training and ensure regular competency assessments.