The helicopter involved in a crash which killed the owner of Leicester City lost control after the pilot's pedals became disconnected from the tail rotor, investigators said.
This resulted in the aircraft making an uncontrollable right turn before it spun and crashed, according to a special bulletin by the Air Accidents Investigation Branch (AAIB).
The report revealed that a system linking the pilot's pedals with the tail rotor failed, according to the Telegraph.
An inspection at the crash site found parts of a mechanism had become disconnected and there was a "build-up of black grease" on one component.
The failure of the system led to the pitch of the tail rotor blades being changed "until they reached the physical limit of their travel", investigators noted.
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."
Footage of the incident appears to show that sections of the tail rotor may have fallen off in mid-air.
The AW169 helicopter reached an altitude of approximately 430ft before plummeting to the ground near Leicester City's King Power Stadium.
It was rapidly engulfed in a post-impact fire and all five people on board were killed.
Leicester City owner Vichai Srivaddhanaprabha, employees Nursara Suknamai and Kaveporn Punpare, pilot Eric Swaffer and his partner, Izabela Roza Lechowicz - who was also a professional pilot - were all killed in the accident on October 27.
Following the crash, the European Aviation Safety Agency ordered that safety checks should be carried out on the tail rotors of AW169 helicopters and similar models