With Flight Centre's origins being in Australia we have adapted the English spelling of Flight Centre as opposed to Flight Center worldwide. Even though we have close to 20 Flight Centres in Los Angeles and another couple in Chicago we still use the English spelling in the USA although the American spelling is Flight Center. 
Other countries such as South Africa, New Zealand, the United Kingdom, all use the English spelling as opposed to Flight Center. Although the difference is minor, America is the only country where we are located in that spells Flight Center with er as oppose to re which is why you will notice our branding, images and text on all of our web sites as well as all of our print advertising uses the spelling Flight Centre, not Flight Center.