Lubitz, a co-pilot at Lufthansa's budget division Germanwings, is believed to have deliberately crashed a plane into the French Alps and killed 150 people.

The question of what Lufthansa knew about any psychiatric problems may be a factor in its liability in the crash. Germany's Allianz estimates that insurers will end up paying $300 million in claims and costs related to the crash.

Lubitz broke off pilot training for several months in 2009. When he resumed his training, he told the Lufthansa pilot instructors by email he had overcome a period of severe depression. He was first certified to fly commercial planes in 2012.

Under European regulations, pilots with psychiatric conditions should be referred to the licensing authority by aeromedical examiners, who may then decide to restrict the pilot’s licence.

The Luftfahrtbundesamt (LBA), the relevant German authority, on Sunday said it had "no information at all" before the crash about Lubitz's depression.

Lufthansa said that a provision in the new regulation, introduced in Germany in April 2013, safeguarded certain pre-existing fit-to-fly certificates and medical certificates issued by specialized aviation doctors.

Aeromedical centers or aviation doctors could therefore issue extensions to such medical certificates even after the new rules came into effect, the airline said.

"A general and separate duty to refer to the LBA did not therefore arise as a result of the change in the legal position," Lufthansa said.