‍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.

Adequate sleep is essential for cognitive abilities, including speech, memory, creativity, and flexibility, to remain at normal levels. A person who doesn't get enough sleep may work less effectively, be less focused, make more mistakes, become irritable, and 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 examine 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, 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 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 rather than just the length of the sleep while making sleep plans.

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

Setting up your sleep environment to give optimum rest is also advisable. Make the bed cozy and ensure 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, sleeping for longer than eight hours can only obtain up to 16 hours of awake time.

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 worsens 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 sleep lasting between 10 and 30 minutes. A micro-sleep is a highly brief sleep period lasting 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. They are risky and do not help with fatigue.

Arranging Sleep for a Night Flight

Aircrews often have to fly when their bodies would rather be sleeping, and occasionally, they 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, their bodies will approach a 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 get enough sleep for the night shift.

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

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; their body clocks will be out of synchronization again when they return. 

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, up to 29 hours a day. Our free-running body clock is 25 hours, so the crew suffers from four hours of jet lag.

Jet Lag Recovery

Everyone finds their 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, such as eating breakfast and going to bed at home to avoid observing local time.

2) A 24-hour layover

This is the most challenging stopover because it only allows 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

Pilots plan to readjust to the new local time as soon as possible for longer stops.

'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 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.

For example, an Air Tanzania (TC) pilot flies a Boeing 787 directly from DAR (UTC+3) to CAN (UTC+8) for a 24-hour layover. She lands and parks at the gate at 21:15 hours (local time), is driven to the hotel, and arrives at her room at 22:00 hours with no sleep credit. 

The following duty is scheduled to begin at 20:00 hours, giving the pilot 22 hours before her next duty.

For this sleep plan, the pilot requires eight hours of sleep (Rule 1) for the duty day ahead, which must be taken immediately before the wake-up call (Rule 2). The last sleep will begin at (20:00 hours—0800) 1200 hours. 

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

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 of 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. It can result from sleep loss or extended awake periods. Fatigue 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 a 'Fatigue Risk Management System' (FRMS) would investigate any such incidents. The system observes factors including Flight Time Limits (FTL), duty hours, home rest, workload, etc., and then issues a report 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 informative 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.'