Accident Overview
On 17 November 2017 at 1201 UTC, a Cessna 152 (registration G-WACG) and a Guimbal Cabri G2 helicopter (registration G-JAMM) collided in mid-air near Waddesdon, Buckinghamshire. Both aircraft were engaged in training flights and were operating in Class G airspace without an Air Traffic Control service. The collision resulted in the destruction of both aircraft and fatal injuries to all four occupants.
Aircraft and Flight Details
The Cessna 152, manufactured in 1982, was operated by a flying club and powered by a single Lycoming O-235-L2C engine. The aircraft was on its second training flight of the day, with an instructor and student on board. The flight plan included exercises on best rate of climb and glide descent. The Guimbal Cabri G2, manufactured in 2017, was also on a training flight with an instructor and student. It was powered by a single Lycoming O-360-J2A engine and had been conducting a navigation exercise earlier that morning.
Sequence of Events
The Cessna took off from Wycombe Air Park’s Runway 24 at 1146 hrs. It climbed to 4,000 ft, then turned left onto a north-westerly course and began a sustained descent. The helicopter departed at 1147 hrs, climbed to approximately 1,500 ft, and tracked north-west toward Silverstone. Both aircraft followed similar paths, with the Cessna descending from above. Radar data showed that the vertical and horizontal separation progressively decreased until the collision occurred at approximately 1201 hrs.
Witness and Recorded Data
A witness located about 0.5 nautical miles south-west observed the two aircraft just before the collision, estimating they were about 20 m apart. The witness described the Cessna as “gliding down slightly” and the helicopter as “directly underneath” and “rising underneath it.” Radar and ADS-B data from NATS and other receivers provided positions and altitudes. The Cessna’s transponder reported altitude to the nearest 100 ft, while the helicopter’s ADS-B provided more precise data to the nearest 25 ft. The final recorded radar position for the Cessna was at 1201:02 hrs at 1,030 ft; the helicopter’s ADS-B data continued until 1201:03 hrs, with the final altitude near ground level. The accident site elevation was approximately 450 ft amsl, and a debris trail of about 300 m was observed.
Contributing Factors
The investigation noted that the opportunity for the occupants to see the other aircraft was limited because both were following a similar track and were not within each other’s field of view, despite being in proximity for a significant period. Neither aircraft was receiving an ATC service. The AAIB highlighted ongoing work led by the CAA to promote electronic conspicuity aids to mitigate the limitations of ‘see and avoid’. The flying club operating the Cessna issued an Instructor Notice emphasizing the importance of maintaining an effective lookout and performing regular heading changes during prolonged descents.