Definition
Brief, involuntary lapses of consciousness lasting from a fraction of a second up to about 30 seconds, during which a fatigued person stops processing external information even though their eyes may remain open. The person is typically unaware the lapse occurred.
Plain English
Very short moments where a tired person's brain switches off without them realising it. They look awake, but for a second or two they are not actually taking anything in.
Context Anchor
Seen in human factors and fatigue discussions, especially when studying obstacles to staying aware in the cockpit.
Derivation
From 'micro' (Latin/Greek root meaning very small) and 'sleep'. The name captures the key idea: these are tiny episodes of sleep that intrude into waking activity.
Why Pilots Care
A pilot in a microsleep can miss radio calls, altitude deviations, or traffic without any awareness that awareness was lost.
Grounding Statement
A pilot can be looking forward with eyes open and still have the brain briefly drop into sleep for a moment.
Intuition Check
Microsleeps are not just feeling tired. They are actual short sleep episodes that can happen without warning or memory of the event.
Example Sentence 1
After three early-morning legs in a row, the captain caught himself having microsleeps during cruise and asked the first officer to take the controls.
Example Sentence 2
The instructor warned the student to watch for signs of microsleeps when flying late at night after a full day of training.