A trainee pilot was unconscious at the controls of his light plane for 55 minutes as it flew 250km on autopilot over Adelaide and out to sea, an investigation has revealed.

The Australian Transport Safety Bureau's report said the young pilot - who has been suspended from flying - woke to find he had overshot the city's Parafield airport and was heading out to sea.

The Middle Eastern man, who studied with Flight Training Adelaide for a year on an Emirates Airlines scholarship, has returned home after the incident ended his career, the Advertiser newspaper reported.

The pilot, in his early 20s, reported feeling hot and sweaty after the sun began to glare into the cockpit.

"He stated that the sun was directly in his eyes and he found it difficult to look out of the windscreen," the report said.

He climbed to prevent the glare, but blacked out soon after.

"[He] regained consciousness about 55 minutes later over the water and uncertain of his position," the report detailed.

The aircraft appeared on air traffic control radar at 3:30 p.m. "outside controlled airspace" to the northeast of Adelaide.

The plane was on its way out to the Great Australian Bight.

Air traffic control tried several times to contact the man by radio but had no luck.

The pilot finally responded at 4:35 p.m. and was guided back to Parafield.

Flight Training Adelaide chief executive Pine Pienaar said the man was "lucky to survive" the ordeal.

He had 60 minutes of fuel left when he came to.

The pilot later told Mr Pienaar of his "scary experience" when he came to, saying: "I looked up and didn't know where I was."

Mr Pienaar said the trainee pilot's blackout was baffling, given he had previously passed a medical examination for aviators.

"Every now and then a guy has an anomaly no one knows about," Mr Pienaar said.