What goes through a pilots mind when he has exhausted his checklist with no improvement to his current condition? A pilots pathway tosafety is his checklista series of simple, linear steps that bring the comfort of years of knowledge to the cockpit environment during panic and crisis. Pilots who experienced aircraft emergencies when a checklist failed recall the surge of adrenaline and pounding heart-thumpingaccompanying the panicked thought of What now? Now imagine the emergency your checklist failed to address is physiological. Imagine the visceral fear as you feel increasingly dizzy and light-headed with your vision darkening and limbs going numb. Combine the fear with the psychological panic that ensues when you reach that last step of your procedure, and you only feel worse. Mentally put yourself in this moment, and you will understand what numerous fighter pilots in the past decade have called an unidentified physiological event (UPE). Listen to their stories, and you will hear them describe an environment where nothing they were taught worked to save them. High-performance aircraft were built to train and fight. At the advent of fighter aviation, high-performance aircraft flight envelopes stayed well within the human physiological envelope.2 One hundred years later, the F-22 joined the ranks of fighter aircraft with an unaugmented flight envelope that well exceeds the human limits in g-force and altitude.3 Only flight control limiters prevent the inconvenient F-22 passenger from routinely outperforming himself with the pull of a stick. Yet despite the meteoric advancements in aircraft performance during the past 100-plus years, hypotheses about human performance in flight remain largely unchanged.4 Put simply, aerospace physiology has not kept up with high-performance aircraft. As a result, even our most modern fighter aircraft feature life support systems designed against an oversimplified set of assumptions: