DALLAS — Sleep is essential to everyone's well-being and growth. It involves the body refraining from physical activities and interacting with its surroundings. The brain organizes vital mental functions when you sleep, repairs bodily tissues, and replicates DNA for growth, among other things.

For cognitive abilities, including speech, memory, creativity, and flexibility, to remain at normal levels, adequate sleep is essential. A person who doesn't get enough sleep may work less effectively, be less focused, make more mistakes, become irritable, and possibly become a weak link in any team's performance.

If a significant amount of sleep is lost, it will result in fatigue, depression, digestive problems, and an increased chance of errors.

Of course, such issues for aviation workers could have catastrophic consequences, which is why aircrews' sleep, rest, and fatigue patterns are so closely monitored.

In this article, we'll take a look at the chemistry of sleep, sleep planning, time zones, jet lag recovery, and pilots' and flight attendants' perspectives on the matter.

How Do We Fall Asleep?

The human sleep/wake cycle, known as a Circadian rhythm, is the body's internal biological clock. It lasts 24 hours in a stable environment but extends to 25 hours when the environment changes, such as crossing time zones. 

It is controlled by a cluster of nerve cells (neurons) called the Suprachiasmatic nucleus (SCN) located in the hypothalamus, a brain region below the cerebellum. 

The SCN gives the information to the pineal gland to secrete melatonin, the hormone responsible for us falling asleep. 

The SCN has the same path as photo-responsive ganglion cells (melanopsin) found in the retina of the eyes. So when daylight falls, the melanopsin signals are picked up by the SCN, telling the pineal gland to secrete melatonin, making a person fall asleep. [1]

Body temperature also affects our circadian rhythms. As our body temperature drops, the desire to sleep increases. When it rises, the desire decreases. Therefore, it's crucial to consider the timing of physical temperature drops while making sleep plans rather than just the length of the sleep.

To manage and reduce fatigue in the aviation environment, aircrew, including pilots, must carefully organize their schedules and get enough sleep. As aircrew flight schedules vary, there are several acceptable ways to plan their rest.

Setting up your sleep environment to give optimum rest is also advisable. Make the bed cozy and ensure there is enough ventilation or an air conditioner to help the body temperature drop. 

It's also important to exclude daylight from the room with darkness or blue light because melatonin is very sensitive to such light conditions.

Sleep Planning

The sleep/wake cycle is conceptualized as a credit and debt system. This means that a person receives two hours of credit for each hour spent sleeping and one hour of sleep debt for each hour spent awake. The maximum credit allowed is 16. Therefore you can only obtain up to 16 hours of awake time by sleeping for longer than eight hours.

For example, to stay awake for 12 hours, you would need a sleep credit of six hours.

Staying awake beyond this period results in sleep debt or deprivation, which is linked to decreased performance and gets worse with altitude.

Airline crews would aim to sleep for eight hours before a duty so that they could work for 16 hours.

Napping, Micro-Sleeps

A nap is a short amount of sleep that can last anywhere between 10 and 30 minutes. A micro-sleep is an extremely brief sleep period that can last between a fraction of a second and two to three seconds.

Depending on routings and flight times, Pilots are allowed to nap periodically throughout a flight, which improves performance. However, after a nap, they must wait five minutes to gather their thoughts before returning to their duties. They must also be awake for at least an hour before starting a descent.

While naps are encouraged, micro-sleeps are strongly discouraged for pilots. This is because they are risky and do not help with fatigue. [1]

Arranging Sleep for a Night Flight

Aircrews will often have to fly when their bodies would rather be sleeping, and occasionally they will have to sleep when they would rather fly. This creates circadian rhythm disruption and alters body temperature cycles, resulting in sleep issues becoming an occupational hazard for those in commercial aviation.

While operating a night flight, some crew members may try to catch some rest in the afternoon before reporting for duty. However, it will be challenging to acquire any restful sleep because of a sound sleep credit (if the person had achieved a typical night's sleep the night before) and an elevated body temperature that interferes with sleep.

Some may go to bed early the night before and rise early the following day to ensure that by the afternoon, the body will approach sleep deficit and be ready for sleep. This will ensure they have enough sleep credit when scheduled for night shift duty. Alternatively, they may stay up late the night before, sleep later, try to relax in the afternoon, and yet get enough sleep for the night shift.

Airline rostering teams organize shift patterns by assigning personnel to the early, late, night, and so on.

Sleep and Time Zones

Crossing multiple time zones is a way of life for long-haul airline crews. These shifts can lead to cumulative sleep deprivation as they constantly adjust and readjust their circadian rhythm to synchronize with the local time and environment at the destination.

This disruption of an individual's typical body clock (circadian rhythm) by changing the time zones is known as Circadian Dysrhythmia or 'jet lag,' which has many unpleasant effects. These can include inadequate sleep, a lack of concentration, irritability, bowel and stomach disorders, and tiredness. [2]

With the aid of zeitgebers (time givers such as ambient light, body temperature, meal schedule, and street noise), a person's body clock naturally synchronizes to the new local time while changing time zones. However, this lengthy process typically takes approximately 90 minutes per day.

For example, a shift of six hours in the local time on a ten-hour flight from Dar es Salaam (DAR), Tanzania, to Guangzhou (CAN), China, will require about four days for the body to adjust to the Guangzhou local time. Pilots may only have two days before returning to DAR; when they return, their body clocks will be out of synchronization again. 

Also, the effects of jet lag and its recovery depend on the direction of travel, whether west or east. The mnemonic 'West is best, and East is least' as used in navigation is pertinent to this case. It is easier to adjust to jet lag when traveling westward than eastward.

Traveling East (DAR to CUN): CUN is five hours ahead of DAR. This means aircrew will experience a 19-hour day instead of 24 hours. Our Circadian rhythm is 25 hours, meaning the aircrew will suffer from six hours of jet lag. 

Traveling West (CUN to DAR): DAR is five hours behind CUN. Therefore aircrew operating this route will experience more than five hours, making up to 29 hours a day. Our free-running body clock is 25 hours, making the crew suffer from four hours of jet lag.

Jet Lag Recovery

Everyone finds their own strategy for overcoming jet lag, although the following are some techniques that are commonly accepted:

1) A short layover (less than 24 hours)

If the stay is brief and the crew returns to base quickly, they continue their hometime routines, for instance, by avoiding observing local time by eating breakfast and going to bed at home.

2) A 24-hour layover

This is the most challenging stopover because it does not allow for two good sleep periods but is too long to complete in one. With this, crews should relax briefly when they arrive so that their bodies will be better prepared to sleep for an extended time before reporting for duty.

3) More than 24 hours of layover

For longer stops, pilots plan to readjust to the new local time as soon as possible.

'Three in One Rule'

It is advised that aircrew base their sleep calculations on the 'Three-in-One' rule to guarantee that they get the maximum amount of beneficial sleep before reporting to work to fly. Three straightforward guidelines make up the rule - 

Rule 1: One hour of sleep results in two hours of being awake.

Rule 2: The required sleep must be taken immediately before the wake-up call for duty.

Rule 3: Three in one rule, (Rule 1 gives units of three hours which we can use to calculate the required amount of sleep needed.

As an example, an Air Tanzania (TC) pilot flies a Boeing 787 direct from DAR (UTC+3) to CAN (UTC+8) for a 24-hour layover. He lands and parks at the gate at 21:15 hours (local time) is driven to the hotel and arrives at his room at 22:00 hours local time with no sleep credit. The following duty is scheduled to begin at 20:00 hours, giving the pilot 22 hours before their next duty.

For this sleep plan, the pilot requires eight hours of sleep (Rule 1) for the duty day ahead, and this must be taken immediately prior to the wake-up call (Rule 2).

Last sleep will begin at (20:00 hours - 0800) 1200 hours. 

The pilot has (2200 hours - 1200 hours) 10 hours before he/she must go to sleep to ensure the maximum amount of sleep credit.

Using the 'Three in One Rule,' divide ten hours by three and find that three hours and 20 minutes of sleep are required.

So the sleep can be planned and taken as shown in the table below:

StateLocal time Sleep/ Wake Hours Sleep Credit Sleep 2200 - 01203:20 hours sleep 6:40 hoursAwake 0120 - 120010:40 hours awake0Sleep1200 - 20008:00 hours sleep 16:00 hours

Captain Chesley "Sully" Sullenberger, said that without adequate rest, his emergency landing in the Hudson River on January 15, 2009, may not have been successful.

During an interview with ABC News on February 9, 2011, he commented, "I'm convinced that had we been tired, had we not gotten sufficient rest the night before, we could not have performed at the same level. The fact that we got so much right so quickly under that sudden stress is a testament, not only to our training but also to the fact that we had a chance to get sufficient rest." [4]

View from the Flight Deck

Chris Smith, a commercial pilot with over twenty years experience explained, "When it comes to managing fatigue while flying professionally, the key is to be tired when you need to be. I can assure you that getting enough sleep before a red-eye flight or a night flight is easier said than done. Adding changing time zones to the mix can further complicate your body clock. Everyone handles fatigue differently, and changing your diet and getting some exercise can significantly impact your alertness during the flight. The effects can be even more noticeable when flying long distances.

"When exposed to multiple time zones, there are two schools of thought. Should you adhere to your home time zone or adjust to the time zone of your destination? Different people prefer different methods, but I always try to adapt to the local time zone because I believe it is easier to change my eating times to correspond with the local time at my destination. Aside from diet and exercise, exposing your body to daylight, and even better, direct sunlight works wonders in resetting your body clock to your new time zone. Few aircrews can claim to have mastered the art of flying at odd hours or across multiple time zones. Rather, it is something that requires continuous improvement!"

A Flight Attendant's Perspective

Lee Cross is a Flight Attendant for a UK airline. He explains how rest is managed within his company, "As aircrew, we must have enough rest between our duties to ensure that the safety of our flight will not be affected."

"Our airline scheduling teams are there to build our rosters to give us sufficient rest between flights. However, it is down to the individual crew member to ensure that this rest is adequate for us to be 'fit to fly' for our next duty."

"If we feel that our workload may have been excessive and that we are not sufficiently rested, then there is always the option of reporting fatigued or unfit."

Fatigue is a physiological state of reduced mental or physical performance. This can be a result of sleep loss or extended awake periods. It is a serious issue that can lead to impairment of a crew member's levels of alertness and, therefore, their ability to safely operate an aircraft or perform safety-related duties.

Lee went on to explain how any such incidents would then be investigated by a 'Fatigue Risk Management System' (FRMS). The system observes factors including Flight Time Limitations (FTL), duty hours, home rest, workload, etc., with a report then issued to the crew member. All notifications of fatigue are also sent to the UK's Civil Aviation Authority (CAA).

Disclaimer

Rest periods for air crews vary from country to country, and individual regulators and operators issue guidance and rules.

However, the standard period is 12 hours rest, or the length of the preceding duty if it was longer than 12 hours. For example, if a crew member were on duty for ten hours, they would need 12 hours of rest. However, if they were on duty for 15 hours, they would require a 15-hour rest period.

This article was written as an informative piece and is not meant to be taken as medical advice. Sources:

[1] International Civil Aviation Organization (ICAO), 'Manual for Oversight of Fatigue Management Approaches - Doc 9966, Second Edition 2016.' Pages 2-18.

[2] United States. U.S. Department of Transportation, Federal Aviation Administration, 'Circadian Rhythm Disruption and Flying.' Pages 2 -4.

[3] Oxford Aviation Academy: ATPL Ground Training, 'Human Performance and Limitations, fourth edition.' Page 212.

[4] BRIAN ROSS and DAN LIEBERMAN, 'Capt. Sully Exclusive: Airline Industry Must Take Care of Tired Pilots.'