The 2016 Leonardo AW169 had just taken off mid-pitch and was climbing out of Leicester City’s King Power Stadium. As it cleared the roof, it entered an accelerating and uncommanded right yaw. A rear-seat passenger began to panic.
Pilot Eric Swaffer applied full left pedal to no effect, confessing, “I’ve no idea what’s going on.” He then lowered the collective. Seconds later, spinning out of control, the helicopter crashed into the parking lot next door, killing Swaffer and his four passengers. Thanks to Swaffer’s last-second lift of the collective, the initial impact was survivable, but the post-crash fire was not.
This week the UK’s Air Accidents Investigation Branch (AAIB) concluded that the Oct. 27, 2018 accident was likely caused by the failure of the helicopter’s tail rotor duplex bearing, leading to loss of tail rotor control that “was sudden and irrecoverable.” The bearing connected the control shaft to the tail rotor blades. The AAIB found that the bearing seized due to fatigue, cracking, pitting, shearing, friction, grease degradation, and heat generation.
But was the accident avoidable? Stewarts, a UK law firm representing the families of the deceased, is making a case that it was.
In a statement, the firm charged that the AAIB report revealed that Leonardo did not share flight test results with the bearing manufacturer to confirm the bearing was actually suitable for the application as opposed to a different design. Furthermore, Leonardo did not require routine inspection of critical parts removed from service, including the duplex bearing, to confirm condition and design assumptions as to suitability, and it did not thoroughly consider risk reduction and mitigation for the duplex bearing while fully understanding the implications of bearing failure.
The firm noted that related litigation already has commenced in Italy on behalf of Swaffer and Izabela Lechowicz, a non-rated pilot passenger aboard the accident flight.
Peter Neenan, a partner at Stewarts, charged that mitigating the risk from bearing failure was as “simple as changing the thread direction on component parts”—a measure already implemented on the AW139. Specifically, a left thread on the nut connecting the tail rotor shaft to the actuator lever would have prevented those parts from separating if the duplex bearing failed. Leonardo’s new version of the assembly incorporates that change.
What Stewarts's statement does not mention, and as the AAIB points out in its report, Leonardo had fully satisfied existing Part 29 certification requirements for the AW169. In a statement issued after the AAIB published its report, Leonardo noted that, following the accident, it voluntarily implemented “precautionary inspection and part replacement measures” with regard to the bearing and the AW169, and that the fleet of approximately 150 AW169s “has not been subject to any grounding or airworthiness restrictions since the accident.”
Many of those precautionary measures were later incorporated into mandatory special bulletins by EASA. The AAIB noted, “During the course of this investigation and as a result of findings made, the helicopter manufacturer has issued 16 Service Bulletins and EASA has published nine Airworthiness Directives for the continued airworthiness of the AW169 and AW189 helicopter types.”
The AAIB report illuminates what could be interpreted as a variety of contributory shortcomings in the Part 29 certification process, including:
- No regulatory requirement for Leonardo to share load survey flight test results with the bearing manufacturer.
- No design or test requirements that address rolling contact fatigue in bearings identified as critical parts, even though “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.”
- No routine inspection requirement for critical part bearings removed from service to review for condition and compare against design and certification assumptions.
- No requirement to fully evaluate various failure sequences and possible risk reduction and mitigation measures within the wider tail rotor control system within the certification process.
The duplex bearing that failed on the AW169 was also installed on the larger AW139. After the AW169 accident, the AAIB evaluated AW139 operator records provided by UK and EU airworthiness authorities and found that “a number of bearings were being rejected across a range of operating hours for roughness and axial play” upon mandated inspections.
On Aug. 4, 2020, Leonardo issued Service Bulletins 169-162 and 189-254 that mandated the replacement of a new design duplex bearing within 400 flight hours or four calendar months. The new bearing replaced ceramic balls with steel balls and had an introductory life limit of 400 flight hours.