A pilot yesterday claimed that the type of helicopter which crashed killing a nine-year-old boy had the worst air conditioning system of all the single-seater aircraft he had flown.

Captain Paul Smith was one of the helicopter pilots at an event at Glamis Castle last year, involving the Noel Edmonds charity Airborne, which ended in tragedy when Garry Malley from Dundee died.

Mr Smith was giving evidence at the trial of fellow pilot Robert Hobson at Forfar Sheriff Court yesterday.

Mr Hobson, 56, Nether Moss, Howgate, Penicuik, faces two charges of contravening Air Navigation Orders on July 13 last year at Glamis Castle and Newhouse of Glamis Farm.

One alleges he endangered the helicopter by taking off when visibility was restricted by the misted windows. The second alleges he had six passengers on board when he was only licensed for five.

The court was told that Mr Smith, who was flying a Squirrel helicopter on the day, had 3500 flying hours' experience in Bell Jet Ranger helicopters like the one that crashed when it was being flown by Mr Hobson.

Mr Smith said he had experienced a number of misting up problems in the helicopter and on three occasions it had been so severe that he found himself in an emergency situation.

He said: ''It always happened after take-off with people on board, who were wet and the outside conditions were wet - similar to the conditions on July 13 last year. Prior to take off the conditions would be clear, but as soon as you get airborne it does not take too long before the screen mists up completely and you can't see.''

Mr Smith, who restarted his evidence after the trial had been delayed for a legal technicality, said those conditions were ''very, very infrequent'' and were not dealt with in any flight manual.

He described how he had to take one hand off the controls and use a chamois to wipe the windscreen. After 20 seconds it became clear that wiping was not making any difference and he had to carry out an emergency landing.

Under cross examination from Mr Mike Jones QC, Mr Smith said he was under the impression that another pilot, Captain Frank Noakes of helicopter company Forth and Clyde, was in command of the flying operation.

He claimed Mr Noakes wanted to start flying without briefing the pilots, but, along with Mr Hobson, he had objected.

The trial before Sheriff James Scott continues.