The helicopter carrying the owner of Leicester City span out of control after the pilot's pedals became disconnected from the tail rotor, investigators have revealed.
This caused the aircraft to turn uncontrollably before it crashed, according to a special bulletin by the Air Accidents Investigation Branch (AAIB).
Thai billionaire Vichai Srivaddhanaprabha and four others were killed in the accident on October 27.
The AAIB report revealed that a system linking the pilot's pedals with the tail rotor failed.
An inspection at the crash site found parts of a mechanism had become disconnected. 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 eight-page 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.
Mr Vichai’s employees Nursara Suknamai and Kaveporn Punpare and professional pilots Eric Swaffer and his partner, Izabela Roza Lechowicz, also died in the crash.
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.