RIO DE JANEIRO — Airplane engine makers have fallen short of what they promised airlines, major carriers' CEOs say, a problem vexing an industry that has struggled for years with aircraft shortages and more recently, a doubling of fuel prices. It's a paradox: Engine makers dazzled carriers with more fuel-efficient options for new planes from Boeing and Airbus. But production shortfalls and disappointing reliability with those engines are becoming costly problems, CEOs said in interviews at the