Introduction and background

Lack of sleep is a major contributor to fatigue which, in turn, can profoundly influence flight safety. Insufficient sleep can lead to poor concentration, increased irritability and lethargy. Most people have experienced these symptoms, but despite their experience, many continue to operate with a sleep decrement and therefore put others at risk.

A common misperception is that nocturnal sleep onset is simply a habit pattern based on external cues. However, when no direct time indicators (e.g., watch, radio, newspapers) or indirect time indicators (e.g., lighting, noise, temperature, vibrations) are present, a person will maintain a consistent sleep-wake cycle. The persistence of the sleep-wake cycle reflects the existence of an internal system, the biological clock, that can function autonomously when no time indicators are available.

This Briefing Note provides an overview of: