Sleep researchers have determined that the air traffic controller in the crash of a Lexington, Ky., commuter flight was substantially fatigued when he failed to detect that the plane was on the wrong runway and cleared it for takeoff. Writing in a new study, the researchers say their findings suggest that mathematical models predicting fatigue could lead to schedules that reduce the risk of accidents by taking advantage of workers' sleep schedules and biological, or circadian, clocks.