Photo courtesy of Leonardo
Leonardo is to inspect its fleets of AW169 and AW189 helicopters to ensure that tail rotor servo-actuators are correctly installed as the result of an emergency airworthiness directive issued by the European Aviation Safety Agency Nov. 7.
The U.K. Air Accidents Investigation Branch (AAIB) is investigating the first crash of an AW169 that occurred Oct. 27 outside the Leicester City football club — a crash that killed the team’s owner, billionaire Vichai Srivaddhanaprabha; the pilot; and three others on board.
The aircraft lifted off just after a game and cleared the stadium before spinning out of control, plummeting to the ground in a nearby industrial park and bursting into flames.
Witnesses told BBC that an apparent malfunction in the aircraft tail rotor caused the uncontrollable spinning descent, but AAIB has released no official cause. U.K. media reports have said that large pieces of the tail rotor came off during flight.
"An accident occurred on an AW169 helicopter, the root cause of which has not been identified and the technical investigation is still ongoing," according to the EASA emergency directive Nov. 7. "While the helicopter was on a takeoff phase at low forward speed, a loss of yaw control has been observed. As a precautionary measure, Leonardo issued ASB [alert service bulletin] 169-120 for AW169 helicopters to provide inspection instructions to check correct installation of the tail rotor (TR) servo-actuator and, subsequently, ASB 189-213 with the same instructions for AW189 helicopters, since these have a TR flight control system of similar design to AW169 helicopters."
"The incorrect installation of the TR servo-actuator, if not detected and corrected, depending on the flight condition, could possibly result in loss of control of the helicopter," the directive said. "For the reason described above, this AD requires a one-time visual inspection of the TR servo-actuator installation and, depending on findings, accomplishment of applicable corrective action(s). This AD also requires reporting of inspection results to Leonardo. This AD is considered to be an interim action and further AD action may follow."
In the past few years, Leonardo has employed simulators to train pilots how to recover from tail rotor failures.
In November 2016, Roberto Bianco-Mengotti, an engineer with Leonardo, discussed the company's efforts in a keynote address at the Rotorcraft Virtual Engineering (VE) Conference at the University of Liverpool.
"The Leonardo keynote (Bianco-Mengotti), The Advantages of Virtual Engineering in the Rotorcraft Flight Mechanics Design Process, introduced the triangle of advantages — safety, effectiveness and economy — that virtual engineering offers the aviation community, particularly helicopter manufacturers," Gareth Padfield, a professor of aerospace engineering at the University of Liverpool and the chairman of the conference, wrote earlier this year in a paper for Aeronautical Journal. "A success story for the safety advantage was described relating to tail rotor failure, considered in the design of the AW169 helicopter, to ensure recovery was possible, and to provide guidance on the recovery techniques for pilots."
Padfield told R&WI that Bianco-Mengotti was waiting to comment until after the AAIB finishes its investigation.
"I am not privy to the AW169 design features that impact tail rotor loss or indeed their recommended training practices," Padfield told R&WI asking what design features and training techniques Leonardo had employed to increase the chances of recovery on an AW169 after a tail rotor failure. Padfield said that from the video of the Oct. 27 crash, "it appears that the aircraft begins to rotate clockwise (viewed from above) about 40 seconds after takeoff, which would be consistent with a tail rotor drive failure or control failure with the tail rotor pitch failing at a low value."
"We will have to await the AAIB investigation and analysis to know the full story," Padfield said. "I led a project on tail rotor failures many years ago in response to our Ministry of Defense's concern that the frequency of tail rotor failures was unacceptably high."
Padfield's work in this regard is in Appendices 5A and 10E of the third edition of his 1996 book, Helicopter Flight Dynamics.