What happened
On 31 May 2000, two Piper PA-28-161 aircraft, registrations G-BSLE and G-BFZG, were involved in a mid-air collision at Oxford Airport. Both aircraft were engaged in training operations, each carrying an instructor and a student pilot.
One aircraft, G-BSLE, was performing an instrument flying approach to Runway 20. The aircraft, flying under the callsign Oxford 67, was utilizing specialized instrument screens to allow the student to fly solely by reference to instruments while the instructor maintained a view of the outside.
Simultaneously, G-BFZG (callsign Oxford 64) was operating in the left-hand visual circuit, performing circuits and landings. As the aircraft transitioned from the base leg to the final approach, the instructor observed the other aircraft above and behind at a distance estimated to be 2 nm. However, due to a speed differential of approximately 30 kt, the distance between the two aircraft closed rapidly.
During the final stages of the approach, the air traffic controller, facing a high workload and attempting to identify the aircraft in close proximity, intended to clear the lower aircraft, G-BFZG, to land. Instead, the controller mistakenly transmitted a landing clearance to G-sLE.
As the instructor of G-BFZG initiated a go-around, the aircraft climbed into the path of the descending G-BSLE. The collision occurred at an altitude of approximately 30 to 50 feet. The tail tie-down plate of G-BSLE struck the leading edge of the G-BFZG wing, while the propeller of G-BFZG struck the aileron and flap of G-BSLE. There were no fatalities and no injuries to the occupants of either aircraft.
The investigation
The AAIB investigation examined the air traffic control records, the aircraft's flight paths, and the controller's workload. The investigation established that the controller had recently transitioned to the Oxford unit and was managing a very busy circuit with multiple aircraft. The controller utilized a pin-board to track aircraft, which required manual updates that diverted attention from visual monitoring.
Investigators also analyzed the flight dynamics, noting that while the instructor of G-BFZG believed there was adequate separation, the speed difference between the descending instrument approach aircraft and the climbing circuit aircraft caused the separation to erode much faster than anticipated.