Michael Gallagher, 55, provided "vital" back-up to the Provisionals' active service unit which could have left hundreds dead if the bombs had gone off in the attack in March 1994.
The Glaswegian-born father of three was caught after a two-and-a-half year surveillance operation, involving the Anti-Terrorist Branch, Special Branch and MI5, which followed a tip off-from a neighbour who saw men wearing rubber gloves working in a garage.
Three batches of home-made missiles, packed with Semtex, were fired into the airport from remote-controlled launchers close to the perimeter fence, over five days. One landed on Terminal Four's roof, packed with travellers, while another narrowly missed six cleaners. They all failed to go off.
The attack was widely seen as a blunt verdict on the Downing Street peace declaration four months earlier.
A jury at Woolwich Crown Court, London, convicted Gallagher by 11-1 of conspiring to cause explosions. Mr Justice Richard Tucker told him: "This series of attacks resulted in enormous disruption of services and it was in my view purely fortuitous that there was no injury or loss of life or extensive damage to aircraft, to runways or to terminal buildings."
Gallagher had rented a garage in which a vehicle and bombs were prepared. "Your role may have been a lesser one but it was nevertheless an important one without which this operation could not have been mounted," the judge said.
He praised Mr Garneys, who notified the police after he became suspicious of activities at the lock-up garage near his home in West Hampstead.
An Irishman had knocked at his home and asked him to move his car, which was blocking a garage entrance.
Mr Garneys noticed that the men kept the garage doors closed to prevent him seeing inside. He saw a second man wearing blue rubber gloves holding the garage doors open.
He subsequently discovered the men were working there at night. It was later believed they had been assembling the missiles and launchers then.
Undercover officers staked out the premises and bugged a telephone line.
Gallagher was often tailed around London, and during frequent visits to Northern Ireland and on a trip to Dublin. On one day alone he was followed by 29 operatives as he headed across London to meet someone police are convinced was a leading Provisional.
Hundreds of his conversations at his flat were recorded. Forensic scientists had uncovered a wealth of circumstantial evidence and forensic evidence pointed to Gallagher being a contributor to the Heathrow attacks.
He was also a self-confessed benefit cheat.Reuse content