Manual tracking experiments were conducted to investigate aircraft operator responses. In these experiments, the operators. attempted to track a random reference input. Afterward, the operators specified the workload required for the task. Using this information, operator models were identified and an operator control philosophy was derived. This philosophy was used to develop a controller design method with the standard operator model to reduce the workload. A standard operator model and controller were developed to allow the operator to control the plant easily. This design method was applied to a plant, and a reduction in workload was confirmed.