What could have prompted Lubitz to deliberately destroy the aircraft, killing everyone on board, remained the focus of investigations in Germany.

Officials said Lubitz was not known to be on any terrorism list, and his religion was not immediately known.

He had passed medical and psychological testing when he was hired in 2013, said Carsten Spohr, CEO of Lufthansa, which owns Germanwings.

While the ailment Lubitz had sought treatment for hasn’t been revealed, that he was declared unfit for work is an important detail, aviation analysts say. Pilots are required to maintain their fitness to fly and must tell their airline if they’re found unfit, CNN aviation analyst David Soucie said.

Adapted from http://edition.cnn.com/2015/03/27/europe/francegermanwings- plane-crash-main/

In the sentence “Pilots (…) must tell their airline if they’re found unfit.”, the expression in bold can be replaced by: