Club boss Vichai Srivaddhanaprabha, 60, and four others were killed in the crash outside the King Power Stadium following a game against West Ham.
Investigators said the fault caused the aircraft to make an uncontrollable right turn before it spun and crashed on October 27.
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 Air Accidents Investigation Branch (AAIB) 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 eight-page report, released today, said: "The tail rotor system was first inspected at the crash site.
"This identified that the input lever mechanism was not attached to the control shaft.
"The pin, spacers and one of the locating bearings were missing from the lever.
"The locking nut and pin carrier were found loose in the tail rotor fairing and were bonded together (they should be separate components)."
The eight-page report concluded the failure of the rotor caused the helicopter to violently veer to the right which led to it crashing in a fireball.
It said: "Loss of the feedback mechanism rendered the yaw stops ineffective, allowing the tail rotor to continue changing the pitch of the tail rotor blades until they reached the physical limit of their travel.
"This resulted in an uncontrollable right yaw.
"Whilst the shaft was rotating and a yaw control input was applied, the shaft 'unscrewed' from the nut, disconnecting the shaft from the actuator lever mechanism, and causing the nut to become welded to the pin carrier."
The report also recommended five safety requirements be made to all AW169 helicopters to prevent future tragedies.
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 Srivaddhanaprabha's employees Nursara Suknamai and Kaveporn Punpare, pilot Eric Swaffer and his partner, Izabela Roza Lechowicz – who was also a professional pilot – were also killed in the disaster.
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.
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