A short period of time (seconds) when the brain disengages from the environment (it stops processing visual information and sounds) and slips uncontrollably into light non-REM sleep. Micro-sleeps are a sign of extreme physiological sleepiness.

Source: ICAO Doc 9966: Manual for the Oversight of Fatigue Management Approaches


Micro-sleep is normally defined as a sleep episode lasting 15 seconds or less. The person may or may not close their eyes during that time but in any case the processing of external information is interrupted. Also, the person is normally not aware of what they have just experienced and has no memory of their actions (or lack thereof) during the episode. They often assume that they stopped paying attention to their environment rather than recognizing that they have fallen asleep for a short time.

Common symptoms of micro-sleep include:

  • Closing of the eyes
  • Nodding of the head
  • Reduced response to external stimuli, such as sounds or visuals

Micro-sleeps are most likely to occur after sleep deprivation. Therefore, shift workers, such as pilots, air traffic controllers and aviation maintenance personnel are particularly vulnerable.

The primary risk, associated with micro-sleep is the lack of attention in a situation that requires it urgently. For example, a pilot may omit an action required by a check-list and an air traffic controller may not be able to detect a conflict or react appropriately to a system warning (such as an MTCD or STCA alert).

Additionally, a person's situational awareness is often degraded after a micro-sleep episode. This happens because the recent changes in the environment have not been absorbed. 

During a micro-sleep the affected person is likely to not respond to a teammate. If the teammate does not persist in obtaining an appropriate response (which they may be unwilling to do due to e.g. workload or authority gradient) and assume their message has been appropriately received. This poor coordination may later evolve in not following a plan (since one of the participants is not aware that there is one).


Currently, there is no universal treatment recommended for micro-sleep, nor is micro-sleep identified as a sleep disorder or among the diagnostic criteria for any sleep disorder. The following measures can mitigate the issue:

  • Fatigue management. Getting enough sleep or rest before duty is the optimal mitigation against micro-sleep. This includes taking a short nap before a night duty. While this does not guarantee that such an episode could not happen, it greatly reduces the risk.
  • Awareness of the issue. Knowing how and why micro-sleep happens can help people identify symptoms in themselves or in their colleagues.
  • Dual person operations. Pilots and air traffic controllers generally work in teams of two (a PF and PNF in the former case and an EXE and PLN in the latter). Among other benefits, this provides some mitigation against mircro-sleep as well, by e.g.:
    • Detecting symtoms of micro-sleep in a colleague. 
    • Maintaining a conversation. This increases brain activity and thus reduces the risk.
    • Switching roles if appropriate.
  • Taking a break if circumstances permit. Pilots may consider taking in-seat rest in accordance with company policy. 

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