Investigators have established the cause of the fatal Leicester City helicopter crash, and revealed a faulty mechanical connection linking the pilot’s pedals to the aircraft’s tail rotor was to blame.
Leicester City owner Vichai Srivaddhanaprabha, members of his staff Nusara Suknamai and Kaveporn Punpare, pilot Eric Swaffer and another passenger, Izabela Roza Lechowicz, died on 27 October after the businessman’s helicopter crashed following take-off.
The aircraft, a £6.7m 2016 Augusta AW169, reached an altitude of approximately 430ft before plummeting to the ground in a car park next to the King Power Stadium and was “rapidly engulfed in an intense post-impact fire”, authorities said at the time.
Following a six-week investigation, the Air Accidents Investigation Branch (AAIB) concluded the tail rotor failure caused the helicopter to violently veer to the right, resulting in the crash.
Footage of the incident appeared to show sections of the tail rotor may have fallen off in mid-air.
“The evidence gathered to date shows that the loss of control of the helicopter resulted from the tail rotor actuator control shaft becoming disconnected from the actuator lever mechanism,” the AAIB said in its eight-page report.
“Disconnection of the control shaft from the lever prevented the feedback mechanism for the tail rotor actuator from operating, and the tail rotor actuator from responding to yaw control inputs.
“Loss of the feedback mechanism rendered the yaw stops ineffective, allowing the tail rotor actuator 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.
“Sufficient force and torque had been applied to the castellated nut on the actuator end of the control shaft to friction weld it to the pin carrier and to shear the installed split pin.
“The observed condition of the duplex bearing and the increased torque load on the castellated nut that remained on the spider end of the shaft is consistent with rotation of the tail rotor actuator control shaft.
Leicester owner Vichai Srivaddhanaprabha’s helicopter crashed on 27 October outside the King Power Stadium (Reuters)
“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 added burnt-on grease was discovered on a key part of the control system.
It stated: “The control shaft, the locking nut and pin carrier and the duplex bearing/sliding unit assembly were removed from the wreckage and inspected in detail.
“The locking nut on the bearing end of the control shaft was found to have a torque load significantly higher than the required assembly value.
“The inner races of the bearing could only be rotated a few degrees in either direction by hand.
The tail rotor control yaw stopped responding ( AAIB)
“There was a build-up of black grease inside the slider unit around the inboard face of the duplex bearing.
“The section of the control shaft adjacent to this bearing face showed evidence of burnt-on grease and was discoloured along its length.”
In the aftermath of the crash, the European Aviation Safety Agency ordered safety checks on the tail rotors of AW169 helicopters and similar models.
The incident was the first time an AW169 helicopter has been involved in a recorded accident.
The AAIB said it would be continuing to investigate the October crash.