Introduction
On 6 April 2015, a Robinson R22 helicopter, registered F-GLHC, was destroyed during an engine start at Plessis-Belleville aerodrome (60). The helicopter was operated by a company for a local personal convenience flight with a pilot and one passenger on board. The following information is based on the pilot's testimony.
Flight Sequence
The pilot initiated the engine start for a local flight. The collective was in the low position and braked, and the cyclic was also braked. He performed magneto checks at 75% engine rpm and verified the freewheel operation. Upon engaging the governor, which maintains constant rotor rpm by regulating engine power, the helicopter began moving to the left. The pilot confirmed the collective remained braked and at full low pitch, but the movements intensified. He pulled up on the collective, observed no improvement, then lowered it. The helicopter then tipped over onto its left side.
Pilot Information
The pilot, aged 61, held a private helicopter pilot license and had accumulated 81 flight hours on the Robinson R22 at the time of the accident. He reported being surprised by the rapid engine rpm increase after governor engagement and stated he did not think to reduce the throttle.
Conclusion
According to the investigation, the pilot's decision to increase collective pitch while the helicopter was experiencing likely vibratory movements may have amplified these movements or induced ground resonance, leading to loss of control. Vibratory phenomena can occur during engine start due to factors such as uneven ground surface, rotor adjustments, or drag damper condition. Typically, such vibrations cease once the rotor and engine exceed a certain rpm. If they intensify, it is generally recommended to abort the start.