The light aircraft which crashed into a Perthshire hill side on Sunday afternoon may have been travelling to Dundee for engineering work.
Two men named as experienced pilot Andy Thompson and John MacKinnon died in the tragedy.
The plane disappeared from radar shortly after midday. It was en-route from Inverness to Dundee.
The police, coastguard, RNLI and RAF were all tasked with searching land and water in the Carse of Gowrie area.
The wreckage of the plane was later discovered on a hillside between Kinnaird and Abernyte.
Its two male occupants were confirmed dead by Police Scotland shortly afterwards.
It is understood that neither man flying the plane is the owner, who is believed to be contractor James Jack, of Invergordon.
A source at the airport said it was “possible” the plane was heading to Dundee for routine maintenance.
He said: “These aircraft come down every six months, which would be due about now.
“We didn’t know it was coming,” the source added.
“Sometimes they come early and the pilot parks them up.”
Conditions in Tayside at the time of the crash were poor, with low visibility and heavy rain.
The source said he did not know why the pair was flying in such difficult weather.
He said: “It’s very surprising (that they were flying).
“The weather was awful and no one at Dundee was flying at all due to it.
“I can only wonder if weather could have been a factor.
“There are so many things it could have been but the weather would have been particularly challenging.”
A source at Inverness airport said weather conditions in the north of the country had been better than those experienced near Dundee.
He said: “It was a bit better here we had flights going up throughout the day.”
Air accident investigators have begun the hunt for clues to determine the cause of the crash.
A team from the Air Accidents Investigation Branch carried out a search of the hillside at Abernyte.