‘They were so beat that they could not understand words even if an order was clearly expressed. I was too tired to talk straight. Nothing I heard made a firm impression on me. I spoke jerkily in phrases because I could not remember the thoughts which had preceded what I said.’ CPT AJ Patch, Paratroop Company Commander, US Army, Normandy Invasion, June 1944
Paratroopers at Normandy participated in a sustained operation which resulted in debilitating fatigue and a remarkable decrease in their ability to perform.. Even a 30-minute flop on the turf would have doubled the power of these men and quickened the minds of their leaders to ideas that they had blanked out. But no one thought to take that precaution. The military can be indifferent toward commonsense rules by which the energy of men may be conserved in combat.
Operational aircrews also participate in continuous operations with periods of sustained operations. Unlike a ground war missions, aircraft availability and flight duration limit periods of flight. Back on the ground, however, flight planning, management responsibilities or lack of crew rest may generate significant fatigue after returning from the last mission or starting the next one.
Fatigue can result from extended periods of anxiety and exposure to harsh environments. Boring or monotonous tasks may increase feelings of fatigue. It interrupts attention and impairs performance. Short-term or acute fatigue can usually be reduced or eliminated after brief rest periods. However, chronic fatigue is more persistent, produces a wider array of effects, and requires longer recovery periods. For accidents, the overall risk seems to remain fairly constant for the first 8 hours of work (including meal breaks.) Beyond this timeframe, the risk rises steeply, until it is approximately doubled after 12 hours, and trebled after 14 hours. However, trends in alertness and accident data often do not correlate well. On many occasions, performance may be severely impaired without this resulting in an accident. For example, a driver may miss an important sign or even fall asleep at the wheel without being involved in a road traffic accident. However one can readily imagine the effect on mission capability of such lapses.
Sleep, like nutrition, is an absolute necessity for life. In fact, it is possible to die from the stress of sleep deprivation sooner than that from food deprivation. Without sleep or with an inefficient or disrupted sleep we can suffer vigilance problems which can also be life threatening. When denied sleep it becomes one of the most demanding and pervasive drives, eventually forcing us to succumb. In addition to the danger of microsleep (short bursts of unintentional sleep lasting from seconds to minutes), the lack of sleep or consistently poor sleep results in increasingly slowed reaction time, error prone performance and irritability.
It is vitally important to recognize early symptoms of sleep loss, as deprivation will lead to confusion, frequent mental lapses, and even hallucinations. Chronic sleep deprivation is even associated with a lowered immune response.
Sleep is most efficient during the night time phase of one’s circadian sleep/wake cycle. Crews attempting to operate during the sleep phase, normally at night, risk an increased probability of accidents due to decreased vigilance. Every effort should be made to remind crews to be extremely careful during this circadian performance nadir (0200-0600). It makes good sense to permit brief naps to help crews function more effectively, particularly at night. However, it is even more sensible to give crews adequate rest before and after their mission to assure a successful flight.
Short naps of even only ten minutes can make a difference. However, there is the risk of some level of “sleep inertia” or mental sluggishness that can occur after awakening from a nap. This can last from 5 to 20 minutes and tends to be worse with naps extending over 30 minutes. The use of caffeine is not a useful countermeasure to sleep inertia. Some research suggests that training can lessen sleep inertia; this means that the more you nap, the better you get at it. The best time to nap is in the early afternoon and at the usual sleep time.
Sleep optimisation means managing your environment. This includes a properly prepared sleeping area. The sleeping quarters should be dark (i.e. no sunlight!) quiet, cool and absent of any daytime social cues. Mealtimes and meal types are also important factors and must be adjusted for crews on odd shifts or reverse cycle.
The optimum amount of sleep for individuals varies greatly from person to person as well as varying with age. Additionally, one can also “suffer” from too much sleep. Sleeping more than ten hours may cause “sleep drunkenness” and should be discouraged, even after a period of sleep deprivation. This level of sleep inertia usually clears after several minutes but can lead to performance problems after awakening.
Negative moods most often reported are:
• Tiredness, decreased willingness to work
• Depression, less cheerful
• Irritability, decreased initiative
• Feelings of persecution, less sociable
• Inability to concentrate, reduced motivation
Some Basic Principles:
• Aircrews are normally tired before sustained operations begin (preload).
• Sleep cannot be stored or built up prior to continuous or sustained operations but sleep deficit can be reduced (allow 8-10 hours of sleep for a few days before a long mission or period of night time vigilance).
• Performance fluctuates predictably over the day (your circadian rhythm).
• Sleep loss, circadian rhythm disruption, poor nutrition and hard work combine to produce fatigue.
• Fatigue is not due to lack of motivation or attitude.
• Vary duty tasks among individuals and give short breaks whenever possible.
• Poor performance is the ultimate price of fatigue in continuous operations.
• We manage maintenance, fuel and weapons; we can also manage fatigue.
Tips on Creating the Sleep Environment:
• Make it dark! Use black out curtains, no sun exposure.
• Bed should be as comfortable as possible.
• Remove any distracters. TV, radio, computers and telephones.
• Air conditioning (remember you can’t open a window!)
• Soundproofing walls, doors, and windows – consider white noise.
• Assure proper room labelling so no one is unnecessarily awakened.
• Assure mealtimes and meal types are adjusted, repeated sandwiches do not constitute proper nutrition