Image copyright ALAMY

The strain put on airline pilots has been in the spotlight since the co-pilot of a Germanwings flight crashed his plane into the French Alps in March.

French investigators say it was intentional and that Andreas Lubitz had practised a rapid descent on a previous flight. There have also been repeated questions about his mental state.

Meanwhile, the European Commission has announced it is setting up a taskforce of experts to review aviation safety regulation, including pilot health checks, following the crash.

So how much pressure are pilots under?

John (not his real name) found himself exhausted after 36 years in the industry.

He told the BBC: "I just found it impossible to go to work. I felt very close to tears, as I had done on various occasions at the end of shifts, without really understanding what was happening.

"I just couldn't really function on any level."

Multiple flights

His view is that rotas created by computerised rostering programmes to allow the minimum rest periods between shifts, and the pressure for a quick turnaround at airports, are creating unacceptable pressures on pilots.

John said: "We start work very early in the morning. We do very long duty days, with multiple flights during the day.

"The physiological effects on one's body of compression and decompression - it can be extremely stressful as the companies continue to ask for more and more."

Image caption The view from Nova Vida Recovery

We visited the holiday villa in southern Portugal that houses Nova Vida Recovery - a team of therapists that John turned to when he felt he could not go on.

About a fifth of the patients at Nova Vida are pilots and the number is increasing. One of the therapists who runs the clinic told how pilots often cover up a personal crisis.

Andrew Vincent, the centre's director, said: "The psychological testing or psychiatric testing is very limited and a lot of people who have depression or stress can quite easily give the answers they feel the doctor needs in order to tick them off.

"I think because of the stigma behind it, because of the fear of losing the job, a lot of people would keep that hidden."

That is a view echoed by John.

He said: "I think pilots are very go-minded people. They like to get the job done, so they do try to keep on going as long as they possibly can and then finally maybe something snaps."

'Serious'

John was in a minority who had to leave the cockpit for good. Around 90% of pilots who visit Nova Vida do eventually get back to work - but it takes time and continuing help from therapists and their employers.

The International Air Transport Association told the BBC: "The aviation industry takes the issue of pilots' mental health very seriously and is open to well-thought-out ways to make any aviation system even more robust.

"The industry will continue to look closely at its procedures."

Prof Robert Bor, a psychologist working with the aviation industry, believes the annual medical assessment for pilots should be more rigorous.

He said: "Whether it is a rogue trader in a bank, whether it is an airline pilot who is not simply suicidal but homicidal, there is always a risk that that person will literally go under the radar.

"However, with closer monitoring, and more scrutiny of pilots, it is less likely to happen."