What happened
On 10 August 2017, a Rotorsport UK Calidus, registration G-CPTR, was performing a private takeoff from a downward-sloping, wet grass runway at Popham Airfield. During the initial stages of the takeoff run, the pilot engaged the pre-rotator to 200 rpm. While attempting to manage the takeoff, the pilot noticed the aircraft's wheels began to slide forward despite the application of maximum wheel braking.
Distracted by this apparent loss of braking effectiveness, the pilot failed to move the control stick to the aft position before releasing the brakes. As the aircraft accelerated, the pilot eventually pulled the control stick back. This action triggered a rapid roll to the left. The rotor blades subsequently struck the ground, followed by the propeller, which caused the engine to cease operation. The aircraft came to rest on its left side. The pilot, who sustained minor injuries, was able to exit the aircraft by forcing open the canopy.
The investigation
The investigation focused on the sequence of control inputs and the environmental conditions at the time of the accident. Investigators examined the state of the runway, noting the grass was very wet. The investigation also reviewed the pilot's actions regarding the control stick position relative to the release of the wheel brakes. It was established that the pilot's attention was diverted by the sliding wheels, leading to a critical error in the takeoff procedure.