(Bloomberg Businessweek) -- Designing a new commercial aircraft requires huge financial outlays and years of engineering wizardry, and success isn’t assured, as the short-lived Airbus A380 jumbo can attest. Such missteps—the double-decker jet never recouped its $20 billion in development costs before being dropped in 2019—explain why the aerospace industry’s preferred route these days is to tweak, stretch and reconfigure existing mod...