Airlines fly around the globe, mostly with their native crew. Singapore Airlines and Malaysia Airlines are relatively small airlines, but they serve dozens of differentcountries. If a crewmember is ill on route, there is a problem of finding, quickly, areplacement. This is just one example why crew scheduling may be complex, es-pecially when it is subject to regulatory constraints, contract agreements and crewpreferences. Disturbance such as weather conditions, maintenance problems etc.also make crew management difficult.