A catastrophic failure of the rear rotor mechanism was the cause of the helicopter crash outside King Power Stadium that killed five people, including Leicester City chairman Vichai Srivaddhanaprabha, a report has determined.
The Air Accidents Investigation Branch (AAIB)’s final detailed report into the tragedy, which also claimed the lives of pilots Eric Swaffer and his girlfriend, Izabela Lechowicz, plus members of Khun Vichai’s staff, Kaveporn Punpare and Nusara Suknamai, on October 27, 2018, is published today.
The report states there was “seizure of the tail rotor duplex bearing” which initiated a sequence of failures in the tail rotor pitch control mechanism, sending the Leonardo AW169 into an uncontrollable spin, or yaw, which was impossible to recover.
Helicopter Crash Cause Revealed
The helicopter had climbed to 430 feet as it left the centre circle of the stadium at 7.37pm following Leicester’s 1-1 home draw with West Ham United when Swaffer lost control as he began to try to turn right towards the direction of travel. Despite Swaffer applying all the corrective control inputs, the unstoppable spin began and the aircraft began to descend.
Even in an uncontrollable spin and in darkness, Swaffer tried to cushion the landing at 75 feet by raising the collective, the control that determines lift, but the helicopter landed on a stepped concrete surface, which made it come to rest on its left side.
A summary of the report said: “The impact, which likely exceeded the helicopter’s design requirements, damaged the lower fuselage and the helicopter’s fuel tanks which resulted 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.”
The investigation found that flight survey test results by the helicopter manufacturers were not shared with the manufacturers of the tail rotor duplex bearings which failed to assess their suitability, or that the manufacturer did not implement a routine inspection requirement for critical part bearings removed from services for review, but the report noted in both cases the manufacturer were not required to by the regulatory process.
The report also noted there were no design or test requirements that specifically tested for “rolling contact fatigue” in the bearings identified as critical parts and “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 also identified failings in possible risk assessment and mitigation measures within the wider tail rotor control system not fully considered in the certification process, but that the regulatory guidance stated that this was not required.
Preventing Future Tragedies
The investigation involved a multi-disciplinary team of skilled investigators from the AAIB, supported by a wide range of experts from industry, academia, and safety investigation authorities from around the world, and identified the failings on the craft as well as making eight recommendations to the European Union Aviation Safety Agency to avoid future tragedy.
The recommendations include validation of design data by suppliers post-test; premature rolling contact fatigue in bearings; life limits, load spectrum safety margins and inspection programmes for critical parts; and assessment and mitigation of catastrophic failure modes in systems.
“This was a tragic accident in which five people sadly lost their lives,” said Crispin Orr, the chief inspector of Air Accidents. “Our thoughts are with their loved ones, and everyone affected.”
The findings of the report shed light on the specific mechanical failures that led to the helicopter crash. The seizure of the tail rotor duplex bearing initiated a series of failures in the tail rotor pitch control mechanism, causing the helicopter to enter an uncontrollable spin. Despite the pilot’s efforts to regain control, the aircraft descended and ultimately crashed.
The impact of the crash exceeded the helicopter’s design requirements, resulting in damage to the lower fuselage and fuel tanks. A significant fuel leak occurred, which ignited shortly after the helicopter came to rest, leading to an intense post-impact fire.
The investigation revealed several shortcomings in the manufacturing and certification processes. Flight survey test results were not shared with the manufacturers of the failed bearings, preventing a proper assessment of their suitability. Additionally, there were no specific design or test requirements to address the potential failure mode of “rolling contact fatigue” in critical parts.
Furthermore, the report identified deficiencies in risk assessment and mitigation measures within the tail rotor control system. These issues were not adequately considered during the certification process, despite regulatory guidance stating otherwise.
To prevent similar tragedies in the future, the report made eight recommendations to the European Union Aviation Safety Agency. These recommendations include post-test validation of design data by suppliers, addressing premature rolling contact fatigue in bearings, implementing life limits and inspection programs for critical parts, and assessing and mitigating catastrophic failure modes in systems.
The investigation involved a team of skilled investigators from the AAIB, supported by experts from various fields. Their comprehensive analysis of the crash not only identified the specific failures that led to the accident but also provided valuable insights for improving safety measures in the aviation industry.
In conclusion, the helicopter crash outside King Power Stadium was caused by a catastrophic failure of the rear rotor mechanism. The investigation report highlighted various shortcomings in the manufacturing and certification processes, as well as deficiencies in risk assessment and mitigation measures. By implementing the recommendations outlined in the report, future tragedies can be avoided, ensuring the safety of air travel.