LONDON—Bernard Gustin was in the office early March 22 for a regularly scheduled Brussels Airlines management meeting when two bombs exploded at Brussels Airport, devastating his airline’s hub.

Two hundred of the airline’s 230 daily flights had yet to leave when the airport was closed indefinitely. Mr. Gustin and other Brussels Airlines executives scrambled to transition from what promised to be a typical day in the office to extreme-crisis management. They set about rerouting domestic and short-haul flight through nearby...