On a sunny day in Montreal last October, Tom Enders emerged from a Bombardier C Series jet and descended the stairs, smiling and waving to a cheering crowd. The Airbus CEO’s management team had once vowed to crush the C Series and eliminate an emerging competitor. Now, in a surprise move, Airbus was taking a majority stake in the struggling Canadian program at no cost, essentially guaranteeing its survival, keeping it out of the hands of Chinese upstart Comac and upending a long-held ...