Limits for long haul flights at night

In 1997, researchers affiliated with NASA Ames Research Center studied fatigue in long-haul operations.

This study considered a number of factors – duty period, flight delays, sleep prior to flight, workload, pilots own assessment of their fatigue levels, in addition to physiological measurements gathered from pilots during flights via electroencephalogram (EEG), electrooculogram (EOG) and electrocardiogram (ECT).

Microsleeps occurred in flight

The study found that pilots experienced “spontaneous micro-sleeps increased with progressing flight duty.”

In addition:

“During night duty, micro-sleeps were 1.2 per pilot per hour during the first 4 hours, and increased to more than 2.4 during the residual of the flight. A maximum was observed after 7 hours.”

“The correlation between ongoing flight time and number of microsleeps was significant.”

“Episodes of extended microsleeps, that is, alpha-activity lasting longer than 30 seconds, were observed in two cases during the outgoing flight and six cases during the return flight.”

The study’s conclusions and recommendations:

“Flight duty periods of <12 hours during normal daytime can be accepted under the conditions investigated.”

“As a second conclusion, night duty is associated with lower alertness and vigilance than daytime duty. The mainly contributing factors are:

  1. Night duty, since human functioning is depressed during the trough in circadian rhythmicity;
  2. Sleep deprivation, because normal sleep is not possible during day-light hours; and
  3. A long duty period which does not allow breaks for recuperation.

“During night hours, fatigue increases faster with ongoing duty. This leads to the conclusion that 10 hours of work should be the maximum for night flying.”