What happened
On 16 October 2006, a Robinson R44 II, registration G-CDJZ, was involved in an accident at Denham Airfield during a training flight. The flight was intended as a training exercise where the student pilot was instructed to perform the engine start-up and initial checklist procedures alone, with the instructor planning to board once the engine was running and the rotors were stable.
After successfully starting the engine, the student proceeded through the 'starting engine and run-up' checklist. The final step required setting the rotor RPM to between 101-102%, then lifting the collective lever and reducing the RPM to 97% to verify the low rotor RPM warning light and horn. As the student lifted the collective, the helicopter unexpectedly became airborne. The resulting attempt to regain control led to violent control inputs, which caused the main rotor to strike and sever the tail boom. The aircraft remained upright following the impact, and the student pilot sustained no injuries.
The investigation
The investigation examined the sequence of the checklist execution and the student's actions relative to the instructor's briefing. It was established that while the student had performed several starts previously, this was the first time they had managed the entire process without the instructor present. The investigation also noted that the student had exceeded the scope of the briefing by continuing with checklist items beyond the point where the instructor was meant to intervene.
Findings
- The helicopter became airborne unexpectedly during the verification of the low rotor RPM warning system.
- The student pilot's response to the unplanned movement involved violent control inputs.
- The tail boom was severed by the main rotor due to these inputs.
- The student pilot proceeded with checklist items that went beyond the specific instructions provided by the instructor for the solo start-up phase.