The inaugural flight of an Avelo Airlines Boeing 737-800 takes off from Hollywood Burbank Airport to Charles M. Schulz-Sonoma County Airport in Santa Rosa on April 28, 2021. Patrick T. Fallon | AFP | Getty Images In the nearly four years since the Covid-19 pandemic upended air travel, the largest U.S. airlines have returned to profitability. The CEOs of two upstart airlines that...