The Air Accidents Investigation Branch has revealed that the helicopter crash which caused the death of Leicester City chairman, Vichai Srivaddhanaprabha, and four others was caused by a pin which had come loose in the tail rotor control mechanism.
The AAIB said that the disconnected pin resulted in the helicopter becoming unstable and preventing the pilot from controlling it.
Investigators found the pilot’s pedals became disconnected from the tail rotor and caused the aircraft to make an uncontrollable right turn before it spun and fell, hitting the ground in a ball of flames.
The pedals and tail rotor are linked by a mechanism which failed after parts of it had become disconnected and there was a “build-up of black grease” on one component.
The failure led to the pitch of the tail rotor blades being changed “until they reached the physical limit of their travel”, investigators said.
The report stated:
“The initiating cause and exact sequence of the failure that resulted in the loss of tail rotor control is being investigated as a priority.”
“The tail rotor actuator control shaft became disconnected from the actuator lever mechanism.
“The disconnection stopped the feedback mechanism for the tail rotor actuator from operating and the tail rotor actuator from responding to yaw control inputs.”
This loss of the feedback mechanism meant the yaw stops were ineffective and the tail rotor actuator was able to continue changing the pitch of the tail rotor blades “until they reached the physical limit of their travel”.