The Martin-Baker Aircraft Company has been fined £1.1m for failing to address a longstanding mechanical fault in the parachute mechanism of its ejector seats, a fault that led to the death of Red Arrows pilot Flight Lieutenant Sean Cunningham in 2011.
Cunningham was killed on 8 November 2011 when the Mark 10 B ejector seat accidentally deployed while he was making pre-flight checks of his Hawk jet, an accident that had been linked to confusion over the position of a safety pin.
But the parachute built into the seat should have saved his life, and the prosecution hinged on Martin-Baker’s failure to address a known fault with the deployment mechanism.
With no parachute to slow his descent, Cunningham fell from a height of around 60m. He suffered multiple serious injuries and was pronounced dead shortly after being airlifted to hospital.
The firm that pioneered the development of the ejector seat was sentenced this morning at Lincoln Crown Court, after pleading guilty to a breach of Section 3(1) of the Health and Safety at Work Act in January.
As well as the £1.1m fine, the Martin Baker Aircraft Company of Higher Denham, near Uxbridge, Middlesex, has to pay legal costs of £550,000.
In a pre-sentencing hearing last week, the prosecution had argued that the company had put many pilots at risk over the years by not addressing the parachute fault, while the defence suggested that the accident would only happen “once every 115 years”.
The HSE prosecution followed a number of inquiries into the incident, including an investigation by Lincolnshire Policy, a Ministry of Defence Military Aviation Authority investigation and an inquest.
HSE inspectors found that, in the 1990s, two aircraft manufacturers had made Martin-Baker Aircraft Company aware of issues with the mechanism – the drogue parachute shackle and a “scissor” shackle – that should have led to the deployment of the main parachute for the ejector seat.
Where a bolt had been fastened too tightly, then the two components would “jam” when the ejection seat was travelling at zero speed and zero altitude. This is known as a zero/zero ejection, designed to save the lives of pilots at very low speeds or in accidents on the ground.
The graphic below prepared by the HSE’s technical specialists in Buxton, highlights what took place.
The drogue parachute shackle, consisting of a bolt held between two lugs with nuts, is supposed to separate from the scissor shackle to deploy the main parachute. Post-ejection, once the seat is at a given velocity, a lock on the scissor shackle is released, allowing the drogue assembly to be withdrawn.
However, at the time of the accident, the lugs on the drogue shackle became caught on the scissor shackle, due to an “interference fit” between the two which then stopped the parachute being deployed.
An “interference fit” is jamming between two parts in which the external dimension of one part slightly exceeds the internal dimension of the part into which it has to fit.
According to the report by the Military Aviation Authority, the gap between the internal faces of the two lugs on the drogue shackle was 0.098 inches too small.
To overcome the jamming effect, greater force and speed would have been required, which the report put at 50 knots.
Alternatively, the jamming would not have been an issue in a zero/zero ejection if the bolt had been fitted to a “flush” position.
HSE operations manager Harvey Wild said: “Our investigation found that Martin-Baker Aircraft Company failed to take all reasonably practicable steps to protect users from the risk of harm after it was told of concerns regarding the shackles which deployed the main parachute.
“The death of Sean Cunningham was therefore avoidable. Our thoughts today are with his family, who are both devastated by these appalling events and proud of Sean for fulfilling his ambition of becoming a pilot with the Red Arrows.
“We understand that a great deal of time has passed since this tragic event. However, this was an extremely complex investigation and no prosecution could be initiated until after the inquest and other inquiries had concluded.
“We would like to publicly thank Sean’s family for their patience and support throughout.”
According to Martin-Baker, its ejector seats have “saved the lives of 1050 British Royal Air Force and Navy aircrew, with a further 6509 aircrew lives saved around the world”.
In a statement released on 22 January, at the time of its guilty plea, the company said: “This plea was entered following detailed and lengthy discussions with the Health and Safety Executive which have considerably narrowed the issues from when its investigation first started. It should be noted that this was an isolated failure relating to the tightening of a nut during maintenance procedures conducted by RAF Aerobatic Team (RAFAT) mechanics.
“Martin-Baker Aircraft Company has designed and manufactured ejection seats for 73 years and in that time these ejection seats have been flown by 92 air forces, with over 17,000 seats currently in use. Our ejection seats have saved the lives of 1050 British Royal Air Force and Navy aircrew, with a further 6509 aircrew lives saved around the world.
“Martin-Baker’s priority has and will always be the safety of the aircrew who sit on the Company’s seats. We appreciate that the Health and Safety Executive, during this process, has acknowledged this dedication and track record of saving lives.”