History of the Flight
The private flight departed Swansea Airport and completed two circuits on Runway 28. The pilot then brought the helicopter to a hover beside a taxiway intersection and hover taxied clear of the runway on a north-easterly heading. The helicopter turned right onto an easterly heading to enter the apron for parking. Surface wind was reported as 300°/14 kt. During the turn from the taxiway onto the apron, the helicopter continued in an uncommanded turn to the right. The pilot attempted to correct with a left yaw pedal input, but despite full left pedal, the aircraft continued yawing right. During this manoeuvre, the nose pitched down and the main rotor struck the ground. The tail then struck the ground and broke off during the subsequent violent yaw.
The helicopter came to rest on its left side with substantial damage to the tail and rotors. There was no fire. The pilot vacated the aircraft unaided and then reached back into the cockpit to shut off the fuel. The passenger in the left rear seat was briefly trapped by her clothing but freed without great difficulty and helped out by the pilot. The passenger in the left front seat vacated unaided. Paramedics and the airfield fire and rescue service attended quickly.
Engineering Inspection
A subsequent engineering inspection did not reveal any evidence of a pre-existing mechanical fault that could have caused the accident.
Loss of Tail Rotor Effectiveness
A loss of tail rotor effectiveness (LTE) occurs when the tail rotor does not provide sufficient thrust to maintain directional control, allowing an uncommanded yaw that can result in loss of control. LTE causes a yaw opposite the main rotor's rotation; for the Robinson R44, whose main rotor rotates counter-clockwise when viewed from above, the yaw is to the right. LTE is likely while hovering or moving slowly with a quartering tailwind from more than 30° behind dead abeam and may be initiated by an intentional turn. Full opposite pedal input may not suffice unless applied positively and without delay. Increasing power to the main rotor increases the yaw tendency; reducing power assists recovery.
The recommended recovery technique for sudden unanticipated yaw is to apply full pedal to oppose the yaw while simultaneously moving cyclic forward to increase speed, and if altitude permits, reduce power. The tail rotor is not stalled.
Investigation Conclusion
The helicopter was hover taxiing in a light quartering tailwind, conditions that make a loss of tail rotor effectiveness more likely. Having initiated a right turn, the pilot did not maintain positive control, and an uncommanded yaw developed that could not be controlled before the helicopter struck the ground. In the absence of evidence of a pre-existing mechanical fault, the investigation determined the most likely cause was a loss of tail rotor effectiveness while hover taxiing at low speed with a tailwind.