Measures of helicopter pilot proficiency were obtained on several hundred student pilots in the Primary and Basic training phases. Measures were based on students' performance on 75 and 76 tasks (items), for the Primary and Basic phases, respectively. Zntercorrelations of tasks in each phase were subjected to factor analysis. The I2 factor rotation solutions were presented in detail for each phase, and the 18 and 24 factor rotations solutions were described briefly. In almost all cases the same tasks (e.g., RPM; Altitude) tended to cluster together across different maneuvers. The factors are interpreted in terms of the operations performed for each task, and the theoretical and practical implications of the findings are discussed. ' One of the most complex perceptual-motor tasks found in practice is that of flying a helicopter. With the increasing importance of the military role played by the helicopter, it becomes important to develop a better understanding of the factors contributing to proficiency in this complex skill. Initial steps toward this objective require a) the development of adequate measures of helicopter piloting proficiency and b) the identification of the critical components of this task which need to be measured.Considerable recent work has focused on the development of objective pilot proficiency measures (Greer, Smith and Hatfield, 1962;Heimstra, Louis and Young, 1962; Duffy and Colgan, 1963). The present study is the second in our series, which builds on this earlier work in an attempt to better understand the skill components of helicopter proficiency. Our first study (Zavala, Locke, Van Cott, and Fleishman, 1965) modified the procedures developed by Greer, et al and applied factor analysis techniques to the intercorrelations among "maneuver" proficiency scores developed from flights of helicopter pilots at two stages of training (Primary and Basic). This analysis of helicopter pilots followed an earlier study of fixed wing aircraft pilots (Fleishman and Ornstein, 1960). Both these studies identified factors common to the maneuver performances, and showed which maneuvers tend to depend on the same or different skills.A limitation of these previous analyses is that we start with maneuver scores which are already composites of many individual tasks. Definitions of the factors tend to be in more "molar" terms and are difficult to define' in terms of more generalizable behavioral categories. The present study attempts to analyze helicopter pilot proficiency data in terms of the individual tasks which comprise the maneuvers. As before, we will analyze pilot proficiency in both the Primary and Basic training phases. However, instead of factor analyzing the correlations among maneuver scores, we now examine the intercorrelations among items drawn from over 200 individual task scores. As far as we can determine, this more "mo!ecular" *