A senior crash investigator said a thorough examination of the aircraft's wreckage had found no evidence of any malfunction.

Andrew Robinson, 59, an inspector with the Department of Transport's Air Accidents Investigation Branch (AAIB), told a hearing at LAnark Sheriff Court he was shocked at the devastation left by the crash impact.

Mr Robinson was giving evidence at the fatal accident inquiry into the deaths of Mr McRae, 39, his son Johnny, five, and family friends Ben Porcelli, six, and Graeme Duncan, 37.

The chopper came down in a wooded valley near Mr McRae's Jerviswood home just outside Lanark in September 2007.

Under questioning from depute fiscal Kate Meikle, Mr Robinson, who has more than 30 years' experience and helped investigate the Lockerbie disaster, said he had found no fault in the Eurocopter Squirrel. He said: "From the wreckage we concluded that it wasn't a structural failure. We were convinced the aircraft's engine was delivering power.

"There was only a very narrow window of time in which a technical problem could have occurred and we found no evidence of this.

"We were confident that nothing had come off the aircraft prior to hitting the trees. It raised questions why the helicopter was flying in that direction. The flight was on a trajectory that really didn't make any sense."

Mr Robinson said the crash had occurred after the helicopter's tail rotor struck a tree 50 metres from the ground. He said an exam- ination of the scene showed the chopper had been travelling at "high speed".

He added: "We were told the aircraft was preparing to land and I was expecting to see a low-speed accident but the amount of damage suggested a high-speed impact.There was damage to the airframe, the gearbox had been torn out, and the main body was burnt out in an intense fire. The aircraft ceased to be a flying machine as soon as it hit the tree."

Mr Robinson added that the possibility a jammed valve connected to the aircraft's controls contributed to the crash was "extremely remote".

The inquiry before Sheriff Nikola Stewart continues.