The coronavirus has suddenly and unexpectedly created the biggest challenge for the global airline industry since 9/11. Bookings around the world are falling sharply. U.S. carriers are following Asian and European airlines in cutting flights, grounding planes and enacting draconian cost reductions, such as hiring freezes and unpaid leave. Foreign airlines are looking for help from governments, banks and investors. Major airlines are trying to reassure passengers with promises of scrubbed cabins, filtered air and free-flowing…