The crash of a Leonardo AW169 that killed five people at Leicester City Football Club’s stadium in 2018 — including the club’s chairman, Vichai Srivaddhanaprabha — was set in motion by the seizure of a tail rotor duplex bearing, the final report into the accident has found.
That seizure began a sequence of failures in the tail rotor pitch control mechanism that “culminated in the unrecoverable loss of control of the tail rotor blade pitch angle,” the report, from the U.K.’s Air Accident Investigation Branch (AAIB), states.
The AAIB said the tail rotor duplex bearing likely experienced “a combination of dynamic axial and bending moment loads,” which generated enough internal contact pressures to cause lubrication breakdown. This ultimately caused the bearing to seize.
The unopposed main rotor torque and negative tail rotor blade pitch angle led to an increasing rate of yaw rotation — essentially putting the helicopter in an unrecoverable spin. The yaw rotation “made effective control of the helicopter’s flightpath impossible,” the AAIB said.
The aircraft crashed near the King Power Stadium in Leicester shortly after takeoff on Oct. 27, 2018, killing Srivaddhanaprabha, Nusara Suknamai and Kaveporn Punpare (two of his staff members), and pilot Eric Swaffer and his partner Izabela Roza Lechowicz.
It had lifted off from the center spot of the pitch at 7:37 p.m., after the stadium had been emptied following the conclusion of a game. The aircraft moved forward, and then began a climb out of the stadium on a rearward flightpath at a rate of between 600 and 700 feet per minute.
As the aircraft passed about 250 feet, the pilot began to transition to forward flight, pitching the helicopter nose-down and retracting the aircraft’s landing gear.
According to the AAIB’s report, the aircraft “briefly established” a right turn before the increasing right yaw rapidly developed, “despite the immediate application of corrective control inputs from the pilot.”
The aircraft’s flight recorder caught an exclamation of “Hey, hey hey,” from the rear cabin, after which the pilot said, “I’ve no idea what’s going on.”
The AW169 reached an altitude of 430 feet before descending with a high rotation rate. About 75 feet from the ground, the aircraft’s collective was fully raised in an attempt to cushion the touchdown.
The report praised the pilot’s actions in responding to the “irrecoverable” loss of yaw control.
“At night, in a highly unstable helicopter which was yawing uncontrollably and descending rapidly in close proximity to buildings, the pilot managed to cushion the descent sufficiently to render the initial impact survivable for at least four of the five occupants,” it stated.
The helicopter hit the ground “on a stepped concrete surface,” the report noted, coming to rest on its left side. The impact damaged the aircraft’s lower fuselage and fuel tanks, resulting in “a significant” fuel leak. The fuel ignited shortly after the helicopter came to rest, and an “intense post-impact fire” rapidly engulfed the fuselage.
In listing contributory factors, the AAIB highlighted several limitations in the certification process and regulatory requirements. For example, it noted that the helicopter manufacturer — Leonardo — was not required to (and did not) share the load survey flight test results with the bearing manufacturer to validate the original analysis of the theoretical load spectrum. Nor were there design or test requirements that explicitly addressed rolling contact fatigue in bearings identified as critical parts.
“While the certification testing of the duplex bearing met the airworthiness authority’s acceptable means of compliance, it was not sufficiently representative of operational demands to identify the failure mode,” the report stated.
The AAIB noted that Leonardo has issued 16 service bulletins since its investigation into the crash began, while the regulator — the European Union Aviation Safety Agency (EASA) — has published nine airworthiness directives for the continued airworthiness of the AW169, and the larger AW189.
The AAIB has made eight safety recommendations in its report to EASA, which it says “address weaknesses or omissions identified in the regulations for the certification of large helicopters.”
Responding to the report’s publication, Leonardo said it extended its sympathies and condolences to those affected by the accident, but highlighted that the AW169 “continues to be safe to fly.”
Leonardo said more than 150 AW169s are in operation in over 30 countries, logging over 150,000 flight hours across the global fleet. “The fleet has not been subject to any grounding or airworthiness restrictions since the accident,” Leonardo said in its statement.
The company noted that the AAIB has not directed any recommended actions to it, and that the report concludes the manufacturer complied with all regulatory requirements in the design and manufacture of the AW169.
“It is important to note that that the substantial work undertaken in five years of analysis, data gathering, investigation and tests of the AAIB’s investigation has been able to identify only a ‘likely’ cause of the failure,” the company added. “We have, together with the Agenzia Nazionale per la Sicurezza del Volo (ANSV), the Italian civil aviation safety investigation authority, made submissions to the AAIB and raised a number of additional points in respect of certain matters.”
Editor’s Note: This story has been updated to include Leonardo’s response to the AAIB report.
