They didn't know about the torn-up doctor's note found in his home, or another sick note excusing him from flying the very day he crashed Germanwings Flight 9525 into the French Alps.
Lubitz had never come forward with any problems.- LIVE BLOG | Germanwings crash
How and why the 27-year-old apparently hid his illness is now the focus of investigators and is also putting renewed scrutiny on pilot screening, and whether mandatory psychological tests could have prevented Lubitz from downing the airliner, killing all 150 people on board, as is alleged.
All the rules governing international flights are based on standards set by the International Civil Aviation Organization, notes aviation safety expert Suzanne Kearns.
Must 'self-identify' psychological issues
But Kearns, an associate professor who teaches about human factors and aviation safety at Western University, says those regulations largely focus on physical well-being and what to do in the event a pilot becomes incapacitated or suffers a heart attack in the air.
"You would get an electrocardiogram for your heart, audiograms for your hearing, they'd check your vision for colour-blindness, check your weight," she said.
"But there's not been much of a focus on mental health."
Pilots are only required to "self-identify" if they've been seeing doctors for mental health issues, as well as declare whether they're taking medication or dealing with mental problems.
For most pilots, who have spent years of studying and between $50,000 and $100,000 spent on flight-school training, there would be little incentive to do that, though.
"The reality is they all know if they lose their medical, they have no careers," Kearns said.
Hard to test for mental illness
In Canada, annual physicals for commercial pilots are performed by Transport Canada-approved doctors.
Pilots 40 and older would be required to obtain a medical certificate every six months.
However, the most rigorous "category 1" medical certificates do not include a psychological testing component.
The international Aerospace Medical Association published a 2013 report recommending more mental health screening among pilots following the apparent mid-flight panic attack suffered by JetBlue captain Clayton Osbon.
While Philip Scarpa, president of the association, acknowledged "there's room for improvement" for mental health screening of pilots, he said "it's a nebulous topic because mental illness is hard to test for."
"Depression, anxiety, mania, alcohol and drug abuse -- those things can be asked about during periodic aeromedical exams," Scarpa said.
"The caveat is it needs to be effective, and trying to look for the serious sudden psychological diseases is not going to be effective."
Until psychological tests can be perfected and guarantee against false positives, he said, it would be difficult to begin grounding pilots.
Sick note not enough
During medical certificate assessments, a doctor can note down any suspected psychological triggers or symptoms in a "Remarks" section.
In Lubitz's case, however, doctor sick notes for an undisclosed illness would not have been enough to stop him from flying.
That might only have been possible had he outed himself or admitted he was suffering from anxiety – something Kearns said pilots have a hard time acknowledging.
For its part, the Aerospace Medical Association suggests the adoption of "safe zones" designed to encourage pilots under psychological distress to self-report. These could go a long way towards changing the stigma surrounding mental illness, it says.
When his mother passed away, James Phillips, the international affairs director with the German Pilots Association, relied on an aviation support line.
"I called and said, 'I'm not fit to be in the cockpit because I am concentrating on my mother,' and my airline said, 'Take two weeks off. Call us when you feel better,'" Phillips told CBC News Network.
"I think this should actually be the real way to go forward, but I realize it's based on a trust and honesty situation, which sometimes is very difficult."
Losing flight hours is another concern for younger pilots making meagre starting salaries, Kearns said.
If a pilot feels momentarily unsafe or unfit from a mental health perspective, it is hard to see how that wouldn't be perceived as a permanent career-ender, she said.
As for how rules surrounding a pilot's mental health status would square with privacy, Minister of Transport Lisa Raitt told CBC News Network that Canada's Aeronautics Act includes provisions to ensure the privacy of a pilot is protected in such cases.
"There will be information given to the airline as to why their pilot doesn't have a certificate of fitness, but really the medical treatment — the dossier itself — is kept very private between the individual and the Transport Canada-affiliated doctor," she assured.
One way or another, Kearns expects aviation safety management systems will increasingly consider mental health disclosure guidelines in light of the Germanwings disaster.
"The reality is the culture will have to shift before anything can change, though," she said.
"Pilots have to learn mental health is not something you can tough out, or just grin and bear. It's something we need to encourage people to seek treatment for."