Pasadena-based Tetra Tech Inc. announced that it has signed a contract with the U.S. Air Force Air Mobility Command to provide environmental engineering services. The five-year contract is valued at $100 million. . . . Washington-based Host Marriott Corp. said it completed the previously announced sale of 26 Fairfield Inns for about $115 million to a venture formed by Sage Hospitality Resources Inc. and Carlyle Group. . . . Mexico’s Grupo Dina consortium has completed the purchase of Phoenix-based bus maker Motor Coach Industries International in a $300-million deal.