Qantas cleared international pilot Paul Whyte to fly one month before police believe he deliberately crashed his light aircraft into the ocean off northern NSW.

The Lennox Head man passed a mental health check in February even though he had been struggling to deal with a marriage breakdown for nearly a year.

Qantas confirmed the father-of-two had flown Boeing 747 aircraft with a capacity of 467 passengers on the Brisbane to Los Angeles route as a first officer in the weeks before his death on Monday.

The Australian and International Pilots Association has repeatedly declined to comment saying "we are not obligated" to speak about the incident, despite Mr Whyte officially representing the union at Civil Aviation Safety Authority meetings in recent years.

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Revelations Mr Whyte was cleared for duty have raised questions from mental health experts about the quality and frequency of checks.

Griffith University psychiatrist Harry McConnell said mental health checks could not pick up sudden changes in stability and called for pilots to more readily report warning signs of their peers to managers.

"Even if he had a mental health screening, it would only have been valid at the time," he said.

"Even if he wasn't suicidal a month ago, obviously there was something that happened in the interim that has changed his way of thinking and his mental state.

"These peer programs like they have in North America are good for that and lets mates to look out for mates.

"It would allow airlines to keep track of mental health on a more immediate level."

A Qantas spokesman said all pilots had annual health checks which involved "a number of physical and psychological tests".

The tests rely heavily on pilots themselves reporting any "significant" change in their health to obtain a medical certificate.

"Pilots who have a history of psychosis, alcoholism, drug dependence, personality disorder, mental abnormality or neurosis are disqualified from holding a Class 1 medical certificate - therefore cannot be a commercial airline pilot," he said.

"As per CASA regulations, all Qantas pilots undergo annual medical evaluations in order to maintain their flying licence.

"This includes a number of physical and psychological tests conducted by a designated aviation medical doctor in a process overseen by CASA.

"Paul passed his annual medical check in February this year. He also passed his proficiency check in November 2015, which includes simulator testing."

The spokesman added: "There are a number of failsafes from a safety of flight perspective, including the 'two in the cockpit' rule that was introduced last year.

"On most international flights there are generally four pilots on board each flight."

Qantas Chief Pilot Captain Richard Tobiano told the Gold Coast Bulletin the tragedy was "very upsetting" for Mr Whyte's "family, friends and colleagues".

"It is with great sadness that I confirm that an off-duty Qantas pilot was flying a light aircraft which went missing off the northern coast of New South Wales on Monday evening," he said.

"As you can imagine this is a very upsetting time for his family, friends and colleagues, and we're providing them with as much support as we can.

"I ask you to respect their privacy at this time.

On Monday the father of two rented a Cessna 172 from the Northern Rivers Aero Club in Lismore, sent a final text message to his family and crashed the plane six nautical miles offshore from Byron Bay. Qantas has confirmed he was in cleared for active duty on the day he died.

Where to get help:

Lifeline: 0800 543 354 (available 24/7)
Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
Youth services: (06) 3555 906 (Palmerston North and Levin)
Youthline: 0800 376 633
Kidsline: 0800 543 754 (available 24/7)
Whatsup: 0800 942 8787 (1pm to 11pm)
Depression helpline: 0800 111 757 (available 24/7)
Samaritans: 0800 726 666 (available 24/7)
If it is an emergency and you feel like you or someone else is at risk, call 111.

- news.com.au