Preface.

The article presents two papers on airlines, discussing two standard and fundamentally important problems of the industry, aircraft scheduling and crew scheduling. In recent years, the world's airlines have experienced several momentous changes in their operating environment: increased exposure to overt or covert market competition-especially in the U.S. following airline deregulation in 1978; dramatic shifts in cost structures with greatly increased fuel and station costs; much lower rates of demand growth in most parts of the world as the industry finally enters its "mature" phase; and increased emphasis on computer-intensive and data-intensive reservations and marketing systems. It is a safe guess that many of the existing planning methodologies and techniques will have to be revised in view of these changes, thus providing important opportunities for further innovative work in this area. It has been seen that airport capacity is fast becoming a scarce commodity at several major cities in North America and Western Europe. Much concern has also been expressed about the strains that the ATC system has been experiencing in the U.S. and about what that implies for aviation safety.