The prediction of pilot workload early in the design process is of primary importance. To develop a predictive model of pilot workload it is necessary to determine what information a pilot uses in rating the workload of a mission segment or tasks. Pilot ratings of workload may be influenced by the rate at which work is done or the amount of work that is done. Results from this study strongly suggest that pilots were sensitive to the rate at which work was done rather than the total amount of work accomplished. A second objective of the study was to predict the workload ratings obtained in the cruise and initial approach segments of simulated flight. Workload values obtained from previous research were combined utilizing a time-based algorithm. The results indicated that the time-weighted average of the component workload ratings were able to predict the obtained workload ratings accurately. This study showed the feasibility of predicting actual inflight workload by using a time-based algorithm to combine tasks and flight segment workload ratings from an empirically derived data base.