US investigators are scrambling to understand how a young mechanic was able to steal an empty passenger plane from Seattle’s main airport, fly for more than an hour doing tricks and then crash into a forest, killing himself.

The FBI, National Transportation Safety Board and Federal Aviation Administration were all attempting to work out how the 29-year-old ground service agent for the airline Horizon Air was able to carry out the incident.

The 76-seat plane had taken off from Seattle-Tacoma Airport, in the northwestern US state of Washington, on Friday night and was soon accompanied by two F-15 fighter jets which were scrambled into the air.

Attempts were made over radio transmissions to the convince the pilot - named locally as Richard Russell, who had worked for the airline for three and a half years - to land. However he ultimately crashed into Ketron Island, a sparsely-populated area of the state.

Recordings of the conversation between the man and control tower officials captured him sounding excitable, at one point saying he had “a few screws loose” and apologising to his relatives.