Air safety officials say a pilot had been drinking the night before an incident in which a passenger was forced to take the controls.

The pilot of the Piper PA-28 Cherokee appeared to have a seizure and lose consciousness soon after 1:00pm on January 25, about 10 minutes after taking off from Forbes in central western New South Wales.

The sole passenger on board took the controls, turned the plane around and radioed for help.

The Australian Transport Safety Bureau (ATSB) has now released its final report on the incident.

The report details how another pilot towing gliders nearby cleared the surrounding airspace and helped keep the passenger calm and advise him on how to keep the plane airborne.

The Piper circled the aerodrome it had taken off from for more than 20 minutes until the pilot regained consciousness and was able to land the plane.

The ATSB says the pilot advised investigators that he had consumed a moderate amount of alcohol the night before the flight and only slept for five or six hours.

The pilot felt unwell on the morning of the flight and had a cup of coffee but no other drink or food before taking off.

He told ATSB investigators that a doctor advised the most probable cause for him losing consciousness was dehydration.

The report notes guidelines from the US Federal Aviation Authority (FAA) on alcohol.

"The minimum guidelines from the FAA are to wait for at least eight hours after drinking alcohol before commencing a flight," the report said.

"However, a more conservative approach is to wait 24 hours from the last use of alcohol before flying.

"The symptoms of hangovers include headache, dizziness and impaired judgment."