In 1980, NASA-Ames Research Center, Moffett Field, CA, initiated a program to assess flight crew fatigue, determine its potential operational consequences, and provide practical countermeasure suggestions. To assess the extent of the problem, crewmembers were monitored before, during, and after commercial short-haul (fixed-wing and helicopter aircraft), overnight cargo, and long-haul operations. A total of 197 volunteers were studied on 94 trip patterns with 1299 flight segments and 2046 h of flying time. The present paper outlines the program and describes the common methodology used in these studies, which are then presented in detail in the four subsequent papers. The sixth paper offers a synthesis of this work, reviewing the major causes of flight crew fatigue and making specific suggestions about ways to manage it in different operations.