What happened
On 28 September 2016, a Rotorsport UK MTO Sport gyroplane, registration G-CFVG, was performing a private takeoff from Northrepps (Crollmer) Aerodrome in Norfolk. Following a standard pre-flight inspection and engine start, the pilot taxied to Runway 22 and aligned the aircraft for departure. The wind conditions were reported as 8-10 knots, blowing straight down the runway.
The pilot initiated the takeoff sequence by pre-rotating the rotor to 200 rpm, trimming the aircraft fully forward, and applying full aft stick while opening the throttle. While the initial phase of the takeoff appeared normal, the pilot soon sensed an irregularity in the aircraft's handling. Shortly thereafter, the gyroplane rolled to the left and crashed onto its side. The impact caused extensive damage to the propeller, rotor blades, and the cockpit pod. The pilot sustained serious injuries and became trapped within the cockpit until emergency services arrived to extricate him.
The investigation
The investigation focused on the aircraft's pneumatic trim system, which uses compressed air to manage the rotor brake and longitudinal trim. This system utilizes an electric pump and solenoid valves to actuate cylinders. During the pre-rotation phase, air pressure is applied to the nose-up side of the trim cylinder, which moves the control stick aft.
Investigators examined whether a malfunction in this system or an error in the pilot's trim management contributed to the roll. It was noted that while the flight manual does not explicitly require it, standard training at the time suggested pilots should trim forward after releasing the pre-rotator to release any residual pressure. The manufacturer noted that while a pneumatic fault is unlikely to generate enough force to cause such an event, maintaining precise pitch control is critical during takeoff to prevent the rotor blades from striking the ground.
Findings
- The aircraft experienced an uncontrolled roll to the left during the takeoff roll.
- A possible intermittent fault in the pneumatic trim system or the presence of moisture in a solenoid valve may have caused the trim cylinder to receive pressure exceeding the intended 2 bar.
- It was also considered that the pilot may have failed to release the trim pressure by trimming forward after the pre-rotator was released.
- The investigation ruled out retreating blade stall, as the vertical stabilizers remained intact and showed no signs of rotor blade impact.