History of Flight
The student pilot, authorized to perform pre-flight checks and start the aircraft, engaged the rotors and accelerated them to 100% RPM. While checking the low RPM horn and caution light, he raised the collective lever slightly and reduced throttle, but the horn and light did not activate at 97% RPM as expected. After lowering the collective and regaining 100% RPM, he repeated the procedure. As RPM approached 97%, the aircraft began to rotate anticlockwise (as recalled by the pilot) or clockwise (as observed by an external witness). The yaw pedals were centralised. The rate of rotation increased, and the aircraft lifted off the ground. It rotated three or four times, lifted into a two-foot hover, then rolled right and descended onto its right side. The low RPM horn sounded, and the pilot shut off the fuel and master switch before exiting. He sustained minor injuries; no fire occurred.
The accident was observed by a passenger in a nearby helicopter, who reported the R22 rotating clockwise while on the ground, then lifting into an estimated 10-foot hover, pitching and rolling erratically before falling onto its right side. The weather was warm and dry, surface wind from 160° at 13 kt; the aircraft was heading approximately 240°.
Procedures
The Pilot's Operating Handbook (POH) checklist for 'STARTING ENGINE AND RUN UP' includes the final items: cyclic/collective friction Off, governor On at 102-104% RPM, and lift collective slightly while reducing throttle to check horn/light at 97% RPM. A caution warns of nose right rotation on slippery surfaces. The operator's procedure, however, specified cyclic and collective frictions ON and governor OFF for the low RPM check.
Analysis
The aircraft lifted off due to sufficient torque, which would cause a right-yaw tendency unless counteracted by left pedal input; no such input was reported. The surface wind from the left would have provided some weathercocking effect but not overcome the yaw. The external witness observed clockwise rotation, consistent with this torque effect. With collective friction applied, the pilot's ability to make fine inputs was degraded. Once the aircraft became light on its skids and rotating, the applied frictions severely restricted control. With the governor off, rotor RPM was under direct twist-grip control, increasing pilot workload.
The pilot concluded that tight collective friction might have prevented fully lowering the lever after the first attempt, and on repetition, he may have raised it enough to make the aircraft light on its skids, enabling rotation. He noted that tight frictions made control difficult during rotation and liftoff.
Recommendation
The AAIB recommended that Patriot Aviation (the operator) amend their low RPM check procedure to reflect the manufacturer's POH, specifically to have frictions off and governor on. The operator subsequently amended starting procedures to include a radio call to ATC for clearance to start.