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Combine our fear of flying with ignorance about mental illness and you have a cocktail for global insecurity. So it's proved this week with the international focus on the psychiatric assessment of airline pilots following the Germanwings Flight 9525 tragedy, where co-pilot Andreas Lubitz apparently deliberately flew an Airbus A320 with 150 people on board into the French Alps.
Revelations that Lubitz, 27, had battled depression sparked calls for those with a history of the illness to be barred from flying commercial jets. Tabloids ran variations on "madman in the cockpit" headlines on the basis of his treatment for serious depression in 2009 and his apparent recent breakup with his girlfriend. Airlines and regulators worldwide have been besieged with questions about how they vet and monitor the mental health of the pilots who hold so many lives in their hands. And are they doing enough?
When it emerged Lubitz had locked the captain out after pressuring him to take a toilet break, New Zealand's Civil Aviation Authority insisted that airlines operating here must always maintain two staff on the flight deck, with cabin crew stepping in when needed.
In the United States, a Delta pilot felt compelled to assure passengers before take-off that he and his co-pilot were both happily married with kids and (how much this helped is debatable) were ex-military.
Mental health experts found themselves once again defending the millions who suffer from depression and still function perfectly well in society, often while on anti-depressants. They pointed out that though depression may sometimes lead to a lonely suicide, it brings no increased tendency towards mass murder. Whatever drove Lubitz (if the French investigators' theory is ultimately proved correct), it wasn't depression.
This doesn't mean passengers shouldn't be assured that airlines and civil aviation authorities do all they can to ensure those in charge are on top of their game, mentally and physically. The crash came just over a year after the disappearance of Malaysian Airlines Flight 370 after take-off from Kuala Lumpur; deliberate pilot action is the most popular explanation for that mystery. But experts say no amount of psychiatric screening can guarantee that a pilot bent on mass destruction will be picked up or thwarted.
"Can you 100 per cent ensure nothing like this would ever happen? I suspect not - humans are unpredictable," says Dr David Powell, an aviation medicine specialist and former chief medical officer with Air New Zealand.
In this country, as in most, there's a fair chance frequent fliers will have been flown by a pilot who has experienced a depressive illness.
"There will be people with depression flying airliners in most developed countries in the world and that's healthy," Powell says. Pilots diagnosed with depression are grounded but with treatment, and following assessment, they can be back in the cockpit in as little as three months. "If you don't have that in place you drive it underground."
Professor Craig Jackson of Birmingham City University told MailOnline that workplace suicide rarely occurred after someone had a bad day. "It happens when several very serious things have gone wrong," he said. "It is complex end-stage behaviour and it comes to a point when the person ... prefers death to life.
"They become completely tunnel-visioned and almost engage in a form of social protest by killing themselves while they are working - and their death becomes a symbol for their dislike for the company or job.
"[Lubitz's] mental health may have been fine but certain aspects in his personality coupled with some stress . . . could be a catalyst for the incident."
Jackson said Lubitz's actions resembled those of a spree-killer - "the type of person who goes on a shooting spree on a campus, school or army base as a social protest because they can't cope any more."
German prosecutors say Lubitz had undergone prolonged therapy for "suicidal tendencies" before getting his pilot's licence. But Lufthansa, the parent company of Germanwings, is regarded as an industry leader in vetting pilots. Lubitz had passed suitability tests after his break in training for depression six years ago and was classed as 100 per cent fit to fly.
Because of the responsibility they bear, pilots are one of the most scrutinised professions. The rigours of flight training, aptitude tests and airline hiring processes are considered highly likely to sift-out applicants with potential mental health issues. In service, regular flight simulator sessions and route checks (inflight assessment of the captain and co-pilot by a third party) should also reveal any concerns.
Under international civil aviation (ICAO) protocols, pilots undergo at least an annual medical (more frequent with age) by a doctor trained in aviation medicine. It's fair to say the medical examination focuses more on physical faculties - eyesight, hearing, heart health - than mental health. But questions must be asked and the ICAO's manual of civil aviation medicine has detailed guidelines on how to assess for drink and drug use, use of anti-depressants and the gamut of mental illnesses. A history of depression should prompt specific questions to ensure the illness has not recurred.
But mental illness still carries a stigma and many sufferers are reluctant to seek help. Experts say the media's tendency to link mass violence to mental illness doesn't help. Though Lufthansa knew of Lubitz's medical background, his ex-girlfriend has suggested more recent problems may have been hidden because they would jeopardise "his big dream of a job at Lufthansa, as captain and as a long-haul pilot".
Yet airlines in most countries have moved to destigmatise mental illness. Admitting to a problem need not be career-threatening - most airlines have generous sick leave provisions and "pathways" so unwell pilots are kept on the payroll and allowed back after treatment and assessment.
Pilots are legally required to disclose any physical or mental condition - and most take their professional obligation seriously. There are exceptions, of course. Tristan Loraine, a former BA captain who campaigns on pilot welfare in Britain, told the BBC pilots and cabin staff didn't always report personal problems. "I've flown with people who were in no state to be flying. They had domestic problems or financial problems and that would put more pressure on me. You land and say 'maybe you should take a few days off'. You remember those people."
There's been criticism that pilots are not routinely subjected to formal psychological testing but commentators say this would be practically impossible and any assessments can be fallible. "If someone dissimulates - that is, they don't want other people to notice - it's very, very difficult," Reiner Kemmler, a psychologist who specialises in training pilots, told German radio.
Even psychometric testing won't tell you about the person who wakes up different one day, clinical psychologist Professor Robert Bor, author of Aviation Mental Health, told BBC News.
The ICAO manual says psychological testing of crew members is rarely of value as a screening tool. "Personality tests alone have not been proven to be reliable tools to predict mental disorders or to assess with any degree of certainty an applicant's suitability for an aviation career."
Which leaves peer review as perhaps the best backstop: pilots look out for each other, knowing the consequences of staying silent can be catastrophic.
New Zealand's Air Line Pilots Association has just launched an assistance programme, in which a trained psychologist and pilot volunteers will offer help to colleagues identified as under stress. "Things like low mood, stress and anxiety have become more prevalent in society," says medical and welfare director Captain Herwin Bongers. "What we are trying to do is normalise a mental health issue as no different to a blood pressure or vision problem."
Peers are often best-placed to notice any deterioration in mood or performance, Bongers says.
Even so, French air accident investigators say their inquiry will include recommendations on changes to psychological examinations for all airline pilots. Their report will cover "criteria and procedures to identify specific psychological profiles". It will also look at "the logic of locking systems for cockpit doors and procedures for entering and leaving the cockpit".
Meanwhile, airlines and aviation authorities worldwide have moved to ensure two people are on the flight deck at all times, with cabin crew standing in during toilet breaks.
Commercial plane crashes where the pilot or co-pilot is suspected of deliberately bringing down an airliner are rare, but not unprecedented.
March 2014: In the absence of any other explanation for the disappearance of MH370, a Malaysian Airlines flight bound for Beijing with 239 people on board, attention focused on the state of mind of Captain Zaharie Ahmad Shah, whose world was said to be crumbling. He had separated from his wife and his relationship with another woman was reportedly in trouble.
Nov 2013: A flight between Mozambique and Angola crashed in Namibia, killing 33 people. Investigations suggested the accident was deliberately caused by the captain shortly after his co-pilot had left the flight deck.
Oct 1999: An EgyptAir Boeing 767 went into rapid descent after taking off from New York, killing 217. An investigation suggested the crash was caused by the relief first officer, although the evidence was not conclusive.
Dec 1997: 104 people were killed when a Silk Air flight from Indonesia to Singapore crashed into the Musi River in Sumatra. The pilot, said to be suffering from "multiple work-related difficulties", was suspected of switching off the flight recorders and putting the plane into a dive.
1994: An Air Morocco regional jet plunged to the ground, killing 51. Investigators concluded the captain deliberately steered the plane into the ground.
The participant's death was unrelated to the pilot, according to Oranga Tamariki.