P ROCESSING-SPEED theory proposes that much of the age-related decline observed in measures of fluid cognition can be accounted for by age-related slowing in the speed of elementary cognitive operations (Salthouse, 1996). A large body of research shows that both behavioral and brain measures of processing speed can account for a substantial proportion of age-related variance in fluid cognitive abilities (e.g., Birren & Fisher, 1995;Bucur et al., 2008;Kwong See & Ryan, 1995;Lindenberger, Mayr, & Kliegl, 1993;Salthouse, 1991;Taylor, O'Hara, Mumenthaler, Rosen, & Yesavage, 2005;Walhovd et al., 2005). Recently, a large study of twins confirmed that genetic variance for processing speed was a leading indicator of variation in a number of age-related cognitive changes (Finkel, Reynolds, McArdle, Hamagami, & Pedersen, 2009).Nonetheless, a processing speed model alone does not necessarily explain certain aspects of normal age-related decline in fluid abilities (Bugg, Zook, DeLosh, Davalos, & Davis, 2006;Schaie, 1989;Schretlen et al., 2000). In particular, decline in executive function has been proposed as a second mechanism underlying age-related decline in fluid cognition (Buckner, 2004;Dempster, 1992; Hasher & Zacks, 1988;Hasher, Zacks, & May, 1999;West, 1996).Although the best way to measure executive function remains a challenge, it has been suggested that executive function be characterized as a collection of related cognitive control processes, in particular, "updating" working memory representations, "shifting" mental set, "inhibiting" automatic or prepotent response to irrelevant information, and "coordinating" complex, sequential behaviors to reach a goal (Friedman et al., 2008). A number of behavioral and neuroimaging studies have demonstrated links among executive control processes and age-related differences in performance of working memory and episodic memory tasks that stress interference, temporal processing, recollection, or contextual binding (Gray, Chabris, & Braver, 2003;Gunning-Dixon & Raz, 2003;Head, Kennedy, Rodrigue, & Raz, 2009;Hedden & Park, 2001;Kwong See & Ryan, 1995;Taylor et al., 2005). Together the results of these studies imply that when examining the explanatory power of processing speed, it may be advantageous to also examine other cognitive abilities, such as executive function.Relatively few studies have examined the processingspeed theory from a longitudinal perspective (Hertzog, Dixon, Hultsch, & MacDonald, 2003;Schaie, 1989;Zimprich & Martin, 2002 Objectives. The goal of the study was to improve prediction of longitudinal flight simulator performance by studying cognitive factors that may moderate the influence of chronological age.Method. We examined age-related change in aviation performance in aircraft pilots in relation to baseline cognitive ability measures and aviation expertise. Participants were aircraft pilots (N = 276) aged 40-77.9. Flight simulator performance and cognition were tested yearly; there were an average of 4.3 (± 2.7; range 1-13) data points per participant. ...