Background
On the morning of 24 April 2005, an instructor parked a Robinson R22 Beta, registration G-CDBG, at the refuelling area at Sherburn-in-Elmet. Another instructor parked a Robinson R44 Astro, registration G-OLOW, next to the R22. The R22 was intended for local training, and the R44 was to be used for type conversion training with another pilot.
Accident Details
Later, the instructor who had parked the R44 briefed a student to pre-flight and start the R22. After the student started the R22, the instructor joined him. Just prior to lift off, a sudden bang and a massive vertical vibration occurred. The instructor of the R22 then shut down the helicopter and realized that the main rotor blades of his helicopter had collided with those of the R44, which had just started up.
Meanwhile, for the R44 flight, when the instructor and the conversion pilot arrived, they found the checklist missing. The instructor went to find it while the conversion pilot performed the external pre-flight check. As part of that check, the conversion pilot rotated the main rotor blades through 180° to ensure sufficient tip clearance from the adjacent R22, which at that time had not been started. The instructor returned with the checklist, completed internal checks, and proceeded to start the R44. As the R44's rotor blades began rotating, they contacted the blades of the now-running R22. The R44 was then shut down. The R44 instructor later stated that he had wrongly assumed that the pilot who had previously parked the R44 had left adequate clearance between the two helicopters.
Aftermath
No injuries were sustained by any crew members. Both helicopters sustained damage: the main rotor blades were damaged and the engines were shock loaded. The operator subsequently painted measured parking spots in the refuelling area to prevent similar occurrences.