Two amateur pilots were killed when a plane assembled from a kit disintegrated in mid-air, an inquest heard today.

William Mills was flying back to his South Wales home from Cornwall with friend Paul Sweeting when the accident happened.

Newport Coroners Court was told a fault in the way the light aircraft was constructed, which caused it to break up, was invisible to the naked eye.

Civil engineer Mr Mills, 60, of Pontypool, South Wales, bought the Europa Classic in 2000, his wife Diana said.

He was returning from an annual aircraft inspection in Bodmin on the afternoon of June 1, 2007, when the accident occurred.

Mrs Mills said safety was a "top priority’’ for her husband, and that he would not have flown the plane if he knew there was a problem.

She said he was "most fastidious’’ about the maintenance of the plane, and added: "My husband was an extremely keen flyer.

"When the weather permitted it, he was off flying, no matter what.’’ The first Mrs Mills knew of the crash, which happened in a field about a mile from the M4 at Magor, South Wales, was when she saw television news coverage.

"It didn't take me many seconds to realise it was my husband's aircraft that was involved,’’ she added.

Mr Sweeting, a 33-year-old IT consultant from Tredegar, South Wales, was a fellow air enthusiast, his mother Susan Haines said.

She told the hearing the trip to Bodmin was arranged "at the last minute’’, and that she did not know he had gone.

In a statement read to the court, witness Sarah Poole described how she was showing the aeroplane to her son when she saw it "crumble’’ and fall to the ground.

A report by the Air Accident Investigation Branch revealed that the aircraft was at a height of 500ft when its tail was seen to "move up and down rapidly’’ before there was "an explosion without fire and smoke’’ and the engine stopped.

Pathologist Stephen Leadbeatter said the men died from injuries after falling from the plane. Nothing in the men's medical histories contributed to the crash.

Safety warnings were made in light of the crash to stop such an accident happening again, the inquest was told.

Gwent coroner David Bowen said: "Hopefully lessons will have been learned from this tragedy.’’ He said the cause of the incident was a "structural fault in the right wing retaining pin’’.

A hole for a pin had been accidentally drilled off centre, he added, causing gradual distortion of the plane's structure.

Mr Bowen said said: "Until the catastrophic failure took place, Mr Mills would have had no inkling there was anything wrong with the aircraft at all.

"It's particularly tragic this should have resulted in the deaths of two enthusiastic flyers whose above all concern was their safety, and that of the aircraft.’’ He recorded verdicts of accidental death on both men, adding: "If any good has come out of it, it's that lessons have been learned that may prevent future fatalities.’’ Speaking after the inquest, Mrs Mills said: "We are satisfied with the findings from the Air Accident Investigation Branch.

"It was the most tragic accident which we hope will never be repeated.’’