A report into the helicopter crash which killed five people including Leicester City owner Vichai Srivaddhanaprabha has revealed there was significant damage to the tail rotor system.
The helicopter crashed shortly after take-off following Leicester's game against West Ham at the King Power Stadium on October 27.
The Air Accident Investigation Branch (AAIB), who published the report had already revealed they were focusing their investigation on the helicopter's tail rotor.
Video footage of the helicopter carrying the Leicester owner showed the aircraft going into a spin moments before it crashed outside the stadium.
Experts already suspected there had been a mechanical failure that affected the tail rotor - in the days following the crash investigators discovered the levers meant to connect the cockpit pedals to the control shaft of the tail rotor were not attached.
Also, the pin and one of the locating bearings were missing from the lever and the locking nut and pin carrier were found loose in the tail rotator and were bonded together - they should be separate.
The report states that "the evidence gathered shows that the loss of control of the helicopter resulted from the tail rotator actuator control shaft becoming disconnected from the actuator lever mechanism."
The control shaft was found to have a build-up of black grease on it, which had been burnt on not by the fire. The AAIB then scanned some of the components and found some of them had been friction welded together and one of the pins had parts sheared off. There was a build-up of debris, black dust and metallic particles - no grease in its original form was present, which in a hydraulic system is crucial.
The investigation is still ongoing and no definite cause has been established as yet - but the report confirms a severe mechanical fault did occur.