SASLess, it just might have, as they do, been away on the ground for a wee while in between jobs. So, your question of how long it had been in flight is relevant. The AAIB have given a departure time from base but, as yet, no details of where they went or what they did for two hours.
The Scottish Daily Record reported
It’s thought the rail alert was a false alarm as last night, British Transport Police confirmed that no trespasser was found.The chopper was scrambled just after 8.20pm when a train driver reported that he may have struck a man he saw on the line near Larkfield junction at Eglinton Toll.
An emergency services source said: “The police helicopter was looking for a body said to be on a railway line. There is a suggestion that it may have run out of fuel.
I am sure one of the Highland newspapers said that they had been taking part in a search near Inverness earlier in the day, refuelled and returned to base and changed crew.