What happened
On 28 May 2009, a Robinson R4ly R44 Clipper II, registration G-CLPR, was performing a solo navigation training exercise at Goodwood Aerodrome. As the student pilot transitioned to a low hover on a concrete apron near several hangars, the aircraft began to rock from left to right. During the descent, the helicopter experienced a sudden swing to the left, eventually entering a nose-low, right-skid-low attitude.
As the aircraft spun, the main rotor blades struck the ground, causing the blades to disintegrate. The impact sent debris across the apron, where a 1.1 kg fragment of the rotor blade breached a fence and struck a workman, causing serious injuries. The helicopter eventually came to rest on its right side with extensive damage to the airframe and rotor system.
The investigation
Investigators examined the flight sequence and witness accounts to determine the cause of the instability. A witness, a licensed commercial pilot, observed the aircraft rocking and noted that the skids appeared to touch the concrete alternately before the sudden leftward yaw occurred.
Analysis of the flight controls suggested that the pilot may have inadvertently lowered the collective lever, which would have caused the aircraft to swing. The investigation also considered whether the pilot's subsequent attempt to lift the aircraft by raising the collective contributed to the instability. The findings indicated that as the aircraft tilted, the rotor thrust shifted, increasing the roll rate and leading to a dynamic rollover.
Findings
- The aircraft experienced a dynamic rollover triggered by the main rotor blades contacting the ground.
- The sudden leftward swing may have been caused by an inadvertent application of the left yaw pedal or a change in collective pitch.
- The subsequent attempt to recover the hover by raising the collective likely increased the roll rate and angular momentum, making the situation unrecoverable.
- A piece of debris from the disintegrating rotor blade caused a serious injury to a person on the ground.
Safety action
Following the accident, the airfield operator implemented new regulations for the use of the concrete apron near the hangars. Use of this area is now restricted to licensed pilots and experienced students, while less experienced students are required to perform landings on the grass.