The Piper Tomahawk II aircraft took off from Glasgow Airport on Friday afternoon at 16:17.
It stopped transmitting at 16:37, a few miles north east of Drymen in Stirling.
Earlier the plane had taken off from Cumbernauld Airport at 11:46 on Friday morning, before flying 15 minutes to Glasgow Airport.
It stayed there until around 13:00, before doing a two-hour flight north east to Newport on Tay before turning round and heading back to Glasgow.
It was on the ground at the airport for just over an hour before it took off again and started its final flight.
Gavin Birch-Williams, managing director of Glasgow Airport, said: “We are aware of an incident involving a light aircraft that departed from Glasgow Airport.
“This is a deeply tragic event, and the thoughts and heartfelt sympathies from all at Glasgow Airport are with the friends and families affected.”