Concerns about the assembly of parts of an ejector seat parachute were raised with the manufacturer more than two decades before the death of a Red Arrows pilot, an inquest has heard.

The inquest into the death of Flight Lieutenant Sean Cunningham has heard evidence that over- tightening crucial nuts and bolts in the mechanism of the seat could cause the parachute not to deploy properly. Flt Lt Cunningham was killed after he was ejected from his Hawk T1 aircraft while on the ground at RAF Scampton in Lincolnshire and propelled 200 to 300ft in the air, on November 8, 2011.

The main parachute on the Mk10 Martin Baker-built ejector seat did not deploy and the 35-year-old South African-born airman later died in hospital as a result of multiple injuries.

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The inquest has heard that instructions given to those fitting the seats was to tighten a shackle nut and bolt with one or one-and-a-half threads showing.

To over-tighten could prevent the parachute from opening, though some witnesses giving evidence to the inquest, which included RAF staff who worked on or with the fighter jets, said they were not aware of this.

The inquest into Flt Lt Cunningham's death in Lincoln heard from Neil Mackie, who was a reliability support engineer in the quality assurance department at Martin Baker. He has since retired.

The hearing was told that, in 1991, he received a fax from an employee at British Aerospace (BA) about the assembly of the ejector seats. It said: "We've found that it is impossible to achieve a normal one-and-a-half threads through the self-locking nut even when pinching the shackle."

Richard Seabrook, counsel to coroner Stuart Fisher, asked Mr Mackie what he made of the message. He said: "My question was, 'Why are they doing one-and-a-half threads?' Then I realised it was one-and-a-half threads everywhere."

Mr Mackie said he thought "what a silly thing to do", in relation to pinching the shackle because this could also hamper the parachute's effectiveness.

He said he was sure he would have communicated in a phone call to BA that the drogue shackle nut and bolt should not be over-tightened and should not be pinching, and he raised the matter internally with Martin Baker that there could be a "serious tolerance problem and aircraft awaiting delivery".

Asked if he thought the instruction to tighten to one/one-and-a-half threads was incorrect, Mr Mackie answered: "Yes, I would not be happy with that."

The inquest continues.