The AW169 at King Power Stadium minutes before the crash.
Authorities investigating the fatal crash of a Leonardo AW169 in Leicester on Oct. 27 are trying to determine what led to damage observed on the tail rotor duplex bearing, according to a Dec. 6 special bulletin by the U.K. Air Accidents Investigation Branch (AAIB).
"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 bulletin said. "Work continues to identify the cause of the damage observed to the duplex bearing and to establish its contribution to the failure sequence. The AAIB is working with relevant organisations to identify any other factors that may have contributed to the loss of tail rotor control."
On Nov. 21, the European Aviation Safety Agency (EASA) issued AD 2018-0252-E for the Leonardo AW169 and AW189 helicopters--a directive mandating inspections of tail rotor duplex bearings, the "inspection and reinstallation of the TR servo-actuator castellated nut and, depending on findings, accomplishment of applicable corrective action(s)." On Nov. 30, EASA issued AD 2018-0261-E mandating repetitive inspections of the tail rotor duplex bearing and the castellated nut that secures the tail rotor actuator control shaft to the actuator level mechanism.
The AAIB has zeroed in on the tail rotor system as the likely cause of the Leonardo AW169 helicopter crash outside King Power Stadium that killed the owner of Leicester City football club and four other people.
"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," according to the Dec. 6 AAIB bulletin. "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...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 [castellated] nut to become welded to the pin carrier."