The helicopter, which was involved in a crash in which the owner of the Leicester City was killed, lost control after the pilot's pedals were separated from the tail rotor, the investigators said.
As a result, the aircraft made an uncontrollable right turn before spinning and falling, as stated in a special bulletin from the Air Accidents Investigation Branch (AAIB).
The report found that a system connecting the pilot's pedals to the tail rotor failed.
During an inspection at the site of the crash, it was found that parts of a mechanism were disconnected, and "black grease" was deposited on one component.
The failure of the system meant that the tilt of the tail rotor blades "was changed until they reached the physical limit of their stroke," the investigators said.
The report states: "The initial cause and the exact order of the failure that led to the loss of the tail rotor control is a priority."
Images of the incident seem to show that parts of the tail rotor have fallen off in the air.
The AW169 helicopter reached a height of about 300 meters before it fell to the ground near the King Power Stadium of Leicester City.
It was quickly involved in a fire after the impact and all five people on board were killed.
Owners of Leicester City, 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 27 October.
Following the crash, the European Aviation Safety Agency ordered that safety tests on the tail rotors of AW169 helicopters and similar models should be carried out.
In November, the AAIB published its first results in the crash, detailing the movements of the helicopter on October 27.
The helicopter trip