Rest is not sleep: what a crew rest period really gives you

A rest period is time off duty. Sleep is what you manage to do with part of it. The rules guarantee the first and only try to protect the second, and the gap between the two is where most crew fatigue comes from. Below is how the rules define rest, what eats into it, why the time of day matters as much as the number of hours, and how to plan a layover so the sleep actually happens.

What the rules give you

Under the FAA's pilot rest rule, 14 CFR 117.25, a flight duty period must be preceded by at least 10 consecutive hours of rest, measured from release. Those 10 hours "must provide the flightcrew member with a minimum of 8 uninterrupted hours of sleep opportunity." If you can see that the rest won't give you those 8 hours, you must tell the airline, and you can't report until you've had a rest period that does. The same section requires 30 consecutive hours free from all duty in any 168 hours, and 56 hours, including three physiological nights, back at home base after more than a week away on a trip across more than 60° of longitude.

Flight attendants in the US have had 10 consecutive hours of rest between duty periods, with no reduction, since the FAA's 2022 rule, up from 9.

In Europe, ORO.FTL.235 sets rest before a duty away from base at least as long as the duty before it, or 10 hours, whichever is greater. The rule spells out what that has to contain: an 8-hour sleep opportunity in addition to the time for travel and physiological needs. At home base the minimum is 12 hours. Crews also get a recurrent extended recovery rest of 36 hours, including two local nights, at least every 168 hours.

Both sides of the Atlantic use the same word, opportunity, because a rule can't make anyone sleep. All it can do is leave enough room in the schedule for it.

Where the hours go

Ten hours from release is not ten hours in bed. Walk a typical international layover through:

• Release to the room. Passengers off, customs, the crew bus and its traffic, check-in. At a big airport this easily takes an hour or more, longer if the bus waits for another crew.
• Winding down. A shower, something to eat, a message home. Almost nobody falls asleep the minute the door closes.
• Getting ready. An alarm, a shower, breakfast, packing: plan on being up at least an hour before the pickup; less than that is a rush.
• The pickup. Usually an hour or more before the report, to allow for the drive.

Say it takes 90 minutes at each end and half an hour to wind down. Take those from 10 hours and the 8-hour sleep opportunity is already down to about six and a half. That's why the rules talk about an uninterrupted 8-hour opportunity and not just 10 hours. When the bus is late or the hotel is far, the opportunity is what shrinks.

The same eight hours aren't worth the same everywhere

How long you sleep depends on when in your body's day you try. Sleep is regulated by two processes: sleep pressure, which builds the longer you're awake, and the body clock, which opens a window for sleep at night and holds it shut during the day (the two-process model). In your body's night both push the same way. In your body's daytime the clock works against you, and you wake early even with the curtains drawn.

The size of the effect is well measured in shift workers. In a review by Åkerstedt and Wright, EEG recordings of rotating shift workers show that day sleep is 1 to 4 hours shorter than night sleep.

For crews this is the usual case, not the exception. After flying east, a local night of 23:00 to 07:00 can fall largely in your body's afternoon. Eight hours in bed may give five or six hours of sleep. To get eight hours asleep, you need more time in bed, which means starting earlier, and that only works if the arrival nap left enough sleep pressure.

How much sleep, and why it matters

The American Academy of Sleep Medicine and the Sleep Research Society recommend that adults sleep 7 or more hours a night on a regular basis. Less than that, night after night, builds a debt that one long sleep doesn't fully repay.

Time awake matters too. In a well-known study by Dawson and Reid, 17 hours of sustained wakefulness impaired performance about as much as a blood alcohol concentration of 0.05%, and 24 hours about as much as 0.10%. A crew member who got up at 06:00 for an overnight flight east has often been awake 20 hours by block in.

The body clock also has a weakest point. The FAA defines the window of circadian low as 02:00 to 05:59 in the time zone you're acclimated to. Alertness is at its lowest then whatever you do, which is why the timing of breaks in flight matters.

What a break in flight is worth

On long flights the break is the main sleep opportunity, and it is worth less than its length. In a study by Signal, Gander and colleagues, pilots on long-haul flights had a 7-hour break. On average they spent 4.7 hours trying to sleep and slept 3.3 hours, less than half the break. The sleep was lighter and more broken than in a hotel: 70% efficiency against 88%, more awakenings, and almost no deep sleep. Older crew members slept less and more fitfully. Breaks taken early in the flight gave less sleep than later ones.

So count the sleep you actually got, not the length of the break. A break in the bunk takes the edge off the hours awake at block in. It doesn't replace the night.

Planning a layover so the sleep happens

Put together, a few rules of thumb follow.

Count backward from the report. Start from the pickup or report, take off the time to get ready, and you have the latest time to wake. Then decide when to be in bed so that the sleep you need fits before it, allowing more time in bed when the night falls in your body's day.

Keep the arrival nap short when the night is short. After a night flight east you arrive with a lot of sleep pressure. A long sleep on arrival feels good and leaves too little pressure for the night that matters. One sleep cycle of about 90 minutes, with an alarm, is often the compromise. When bedtime will fall in your body's day, even shorter is better.

Go to bed earlier after a long day. If you'd pass about 20 hours awake by your usual bedtime, bring bedtime forward rather than pushing through.

Before a night duty, nap in the afternoon. Sleep in that morning if you can, then nap once more, ending well before you need to get ready, so the grogginess of waking (sleep inertia) has passed by the report.

Speak up when the rest won't work. Under 117.25(f), a pilot who sees that a rest period won't give 8 uninterrupted hours of sleep opportunity must say so, and can't report until it does. Many company fatigue programs have their own way to report it. Use it.

How LogAloft uses this

Every layover before your next duty gets a Rest plan, named for its city. It counts your hours awake at block in from when you got up the day you flew, less the sleep you got in flight. Both are dials at the top of the plan: the first is estimated from your usual hour, the pickup or the report, and the second from your break. Set them to what really happened. It then walks the layover from block in to the report:

• the time to the room;
• a short arrival sleep, or none;
• when to be in bed so that the sleep you can expect reaches 8 hours when the layover allows it, with more time in bed when the night falls in your body's day;
• meals fitted to the hours you're awake;
• getting ready, up at least 60 minutes before the pickup;
• before a night flight, a nap that ends in good time.

Your body clock comes from where you've actually been over the last three weeks, and if you commute it starts on home time. The trip briefing prints the plan for each layover on one page, next to the schedule, the hotel and the pickup.

The plan is for planning, not medical advice. People differ, and it doesn't replace your judgment, your company's fatigue policy or the rules you fly under.

Sources

1. 14 CFR 117.25, Rest period, Electronic Code of Federal Regulations
2. Biden-Harris Administration Extends Rest Periods for Flight Attendants, FAA, October 4, 2022
3. ORO.FTL.235 Rest periods, Regulation (EU) No 965/2012 as amended (text and guidance)
4. The two-process model of sleep regulation: a reappraisal (Borbély, Daan, Wirz-Justice and Deboer), Journal of Sleep Research, 2016
5. Sleep loss and fatigue in shift work and shift work disorder (Åkerstedt and Wright), Sleep Medicine Clinics, 2009
6. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society (Watson et al.), Journal of Clinical Sleep Medicine, 2015
7. Fatigue, alcohol and performance impairment (Dawson and Reid), Nature, 1997
8. In-flight sleep of flight crew during a 7-hour rest break: implications for research and flight safety (Signal, Gander, van den Berg and Graeber), Sleep, 2013
9. Sleep inertia: current insights (Hilditch and McHill), Nature and Science of Sleep, 2019