In addition to suing Lubitz's doctor, the 61-year old man also filed against medical experts in Germanwings' parent company Lufthansa and German aviation authority officials.

German prosecutors were looking into the lawsuits, a spokesman confirmed on Monday.

The litigation comes over a year after the 27-year old Lubitz deliberately crashed a Germanwings plane into the French Alps, killing himself and 149 more people aboard. It was later revealed that the young co-pilot suffered from severe depression.

The crash, in which the daughter and grandson of the accuser were killed, prompted Germany to implement random drug and alcohol tests and boost safety requirements in the cockpit.

Dozens of doctors stayed silent

The plaintiff blames Lubitz's physician for not alerting the airline or the regulators about his mental issues.

"Confidentiality no longer applies, because she knew her patient was a pilot with mental issues that were repeatedly expressed," the man told the German newspaper Die Welt.

Investigators have stated that Lubitz had visited 41 doctors in the months before the crash, and none of them warned the Germanwings administration that he was struggling with depression. In addition, Lubitz himself had reportedly informed Lufthansa about a "severe depressive episode" in 2009, which forced him to put his pilot training on hold. He was later reinstated after doctors declared him fit.

The plaintiff believes that Lubitz should not have been allowed to fly a passenger plane with his history of depression, according to Die Welt.

Earlier this year, some 80 family members used similar arguments to put forward a lawsuit against the Airline Training Center of Arizona, where Lubitz received a part of his training.

Doctors decry Lufthansa

Last month, the head of Germany's doctor' association also criticized Lufthansa for allowing Lubitz to fly.

The association chief Frank Ulrich Montgomery blamed both the airline and the regulators for not monitoring his mental state more carefully.

"As doctors, we find it appalling that both the Federal Aviation Authority and Lufthansa knew that this pilot had records of severe depression but underwent no particular checks," he told Hamburger Abendblatt.

"An annual examination - as is the general rule - is insufficient in such cases," he added.

Montgomery also said that medical controls focused mostly on "physical findings and laboratory tests" but neglected psychological issues.