ValuJet, the low-cost Atlanta-based airline, promised "fun and friendly service" when its super-cheap service began Thursday. Depends how you define fun. On the initial flight to Boston, passengers had to assume the "crash position" when the landing gear malfunctioned. The first flight to Miami caught fire when the engine on the aging DC-9 exploded. All 60 passengers escaped with minor injuries, and maybe a new appreciation for the joys of driving.