As the key source of information for pilots, the human visual system has necessarily driven much of the evolution in cockpit technology. In contrast to the complicated, gauge-based systems of the past, the electronic flight displays of today's modern airliners are testament to advances in human factors engineering. The next step in flight instrumentation, although already used for some 50 years in the military, is just beginning to emerge in civil transport aircraft. Head-up displays (HUDs) allow pilots to see key flight instrumentation while viewing the outside world. The need to look down at the flight instruments is removed by the HUD, resulting in increased situational awareness and greater precision in aircraft control. While the head-up display is a welcome development, as with many instances of human-technology interface, the benefits provided by HUDs are not without potential drawbacks.