What happened
On 13 February 2015, a Robinson R22 Beta, registration G-THLA, was conducting a training flight near Snargate Lane, Romney Marsh, Kent. The session was intended to prepare a student for a General Flying Test, focusing on various autorotation techniques. Following a successful demonstration of a 360° autorotation by the instructor, the student attempted the same manoeuvre.
During the student's turn, the aircraft's airspeed and altitude began to decrease, triggering a low rotor RPM warning. Although the student adjusted the collective pitch to address the RPM drop, the instructor had to intervene by applying power to attempt a go-around. Despite applying full power and pushing the nose down to regain speed, the aircraft continued to descend rapidly. As the helicopter approached a ploughed field at approximately 40 ft, the instructor attempted a flare for a low-speed landing. The rear of the skids struck the ground, causing the front of the skids to dig into the furrows. This caused the rotor system to strike the earth, resulting in the aircraft rolling onto its right side. There were no fatalities and no injuries to the two occupants.
The investigation
Investigators examined the sequence of events leading to the loss of control. The instructor noted that the aircraft encountered a 25-30 kt wind during the flight. The investigation looked into whether the rapid descent was caused by the reduction in collective pitch following the low RPM warning or by environmental factors such as windshear.
Additionally, the investigators considered the possibility of the aircraft entering a 'vortex ring' state, a condition characterized by a high rate of descent, applied power, and low airspeed. However, the instructor's assessment indicated that the go-around was initiated at a speed that should have been sufficient to arrest the descent, leading to the conclusion that vortex ring state was not a contributing factor.
Findings
- The aircraft experienced a significant increase in the rate of descent following the student's attempt to manage the low rotor RPM warning.
- The instructor's decision to lower the nose to regain airspeed further contributed to the rapidly increasing rate of descent.
- The landing site, a ploughed field, contributed to the impact as the skids dug into the earth, leading to the rotor strike and subsequent roll.