Aviation authorities in the US say it's not yet clear why aircraft mechanic Rich Russell stole a plane from an airport - before it crashed on a nearby island.

The 29-year-old died after flying the aircraft in a loop, before nose-diving into the ground near Seattle. 

READ MORE: Baggage handler who stole a plane remembered as 'nice guy'

Control tower operators had earlier tried to convince him to land safely - after he expressed interest in becoming a pilot.

"We'll see what we can do and get you in contact with somebody," the operators told Russell.

"I kinda want to do a couple of manoeuvres to see what [the plane] can do before I put [it] down," Russell replied.

No one else was injured in the incident and there was no one else in the plane with him.

Airforce jets were scrambled.

Richard Russell worked for Horizon Airlines, a sister carrier of Alaska Airlines, as a ground service agent who helped baggage handlers and was part of Horizon's tow team, which moved planes around on the tarmac.

He had said that a perk of the job was being able to take a plane and fly it to Alaska.