Germany’s Bild newspaper reported that the co-pilot, Andreas Lubitz, suspected of deliberately crashing a plane in the French Alps told a former girlfriend he was planning a big gesture. (Reuters)

On the day he appeared to fly a commercial airliner into a chilly mountainside in France, Andreas Lubitz was hiding a potentially deadly secret: a chronic medical condition that a doctor had determined was serious enough to keep him out of the sky.

Among the pile of evidence seized by investigators in Lubitz’s belongings were torn and crumpled doctor’s notes excusing the pilot from work. The notes included a period extending to Tuesday, the day of the crash. The discovery came as investigators probe whether the 27-year-old’s health — including possible psychological problems and a suspected background of clinical depression — played a role in an air tragedy that claimed 150 lives.

Authorities would not reveal the exact nature of Lubitz’s illness. But an official from the German prosecutor’s office in Düsseldorf, speaking on the condition of anonymity because he was not authorized to reveal details beyond an official statement, said that the doctor’s notes were related to a “long-lasting condition.” Asked whether they were also related to psychiatric problems, he said, “Read between the lines.”

The comments came after Germany’s Bild newspaper reported that Lubitz had been treated for at least one “serious depressive episode” so bad that he had to suspend flight training for several months in 2009. On Friday, the Rheinische Post also reported that the medical notes discovered in Lubitz’s apartment came from at least two doctors — suggesting he may have been searching for a favorable diagnosis and possibly feared losing his medical certification to fly.

German aviation authorities said that Lubitz’s medical file, tied to his pilot’s license, contained a notation that he was required to have “special regular medical examinations.” Such citations can relate to a wide range of medical conditions.

The prospect that mental-health problems may have figured in the crash of the Germanwings plane additionally shined a spotlight on what critics call flaws in the regular medical checks required of airline pilots, who must pass as many as two exams per year. Such tests, however, are largely geared toward catching physical ailments, such as vision or heart problems, that could impair performance in a cockpit. Mental-health tests in fitness evaluations are often cursory, sometimes amounting to little more than a written questionnaire.

“Typically, there are no tests applied to identify psychological diseases,” said Andreas Adrian, an aviation doctor who evaluates Lufthansa’s and other airlines’ pilots in Bremen, Germany. “Maybe you are giving someone a questionnaire to answer, but of course, you can get a good actor and he can easily hide any issues.”

The debate intensified on Friday over whether mental health should be more deeply probed — an effort strongly opposed by some pilot groups and others who say that could add to the pressures of an already high-stress job.

More rigorous mental-health testing could “uncover thousands of people who are going through difficult times in their lives and prevent them flying when they are perfectly capable of carrying out their normal day jobs,” said Philip Baum, editor of the magazine Aviation Security International. “You will have to employ far more pilots, and it would be an additional stress and could make things worse.”

The possibility that Lubitz may have hidden his condition — a task that could have been made easier by strict medical privacy laws in Germany — might help explain how he passed his flight training program. Lufthansa chief executive Carsten Spohr said this week that his company, which owns Germanwings, was never informed of the reason for Lubitz’s medical leave in 2009, a period in which the newspaper Bild said Lubitz was suffering from clinical depression.

Yet, even if he did hide an illness, the fact that Lubitz — who lived much of the year with his parents in this quiet, picturesque town in southwest Germany — passed muster at Lufthansa’s demanding flight school with what Spohr called “flying colors” raised additional questions. The course is meant to weed out potentially troubled men and women, using role play scenarios in cockpits to measure reactions to conflict and stress, as well as highly personal lines of questioning to assess psychological balance.

“They have to expect questions about their personal histories,” said Michael Müller, chief executive of ATTC, a company that helps prepare pilot candidates for entering flight schools, including Lufthansa’s. “How did you grow up? Did your parents divorce? How did you feel when they did?”

Under existing aviation laws, any diagnosis of depression or other serious mental illness should have made it difficult for Lubitz to continue flying in Europe, and certainly not without extensive treatment. Even then, certain limitations are placed on pilots who are taking psychotropic medications — such as popular anti-depressants — including a stipulation that they not be alone in the cockpit.

Investigators, meanwhile, sought more answers about the man who German and French investigators believe brought down Flight 9525 on his own.

At Lubitz’s apartment in a leafy middle-class neighborhood on the outskirts of Düsseldorf, neighbors had affixed Germany’s black, gold and red flag at half-staff on a utility pole. Pink camellias bloomed near the entrance to the three-story building, and a small palm tree sat on Lubitz’s balcony.

On the doorbell, the name Goldbach appeared with Lubitz’s. Neighbors said Goldbach was the last name of the woman who lived with Lubitz in the apartment. It was not immediately clear whether they were married.

Lubitz and Goldbach were both reserved but friendly, and Lubitz would from time to time walk along the street in his pilot’s uniform, neighbors said, on at least one occasion stopping to play with a neighbor’s 3-year-old daughter.

A police spokesman outside the building said Friday that investigators had completed their searches a day earlier, spending 3 1/2 hours scouring the apartment and taking away two cardboard boxes and a large bag of Lubitz’s possessions.

The University Hospital Düsseldorf confirmed that Lubitz visited the facility in February and, for the last time, on March 10 for “diagnostic clarifications.” The hospital statement gave no further details, citing medical confidentiality. But it denied German media reports that Lubitz had been treated there for depression.

Its psychiatric and neurologic clinic is a 10-minute drive from Lubitz’s Düsseldorf home, on a rolling campus filled with Italianate buildings.

Birnbaum reported from Düsseldorf. Stephanie Kirchner in Montabaur and Karla Adam in London contributed to this report.

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