Sleep and Fatigue — Page 216, Lesson 348

I want to walk you through how jet lag affects aircrew differently depending on the direction of travel, and then the recovery techniques we use to manage it. Let's start with travelling westwards, using the example of London to New York. New York is 5 hours behind London, so noon in New York occurs 5 hours later than noon in London. This means that an aircrew flying from London to New York will experience a 29-hour day. Now, our free-running body clock — that's the natural internal rhythm our body follows when there are no external time cues — runs on a cycle of approximately 25 hours. Because the crew's day is 29 hours long, but their internal clock expects a 25-hour day, they will suffer from 4 hours of jet lag. Jet lag, in this context, is the mismatch between the local time and the body's internal clock. Now let's look at travelling eastwards, using New York to London. London is 5 hours ahead of New York, so noon occurs 5 hours earlier. This means the aircrew will experience a 19-hour day. Again, our free-running body clock is 25 hours. Because the day is 19 hours long — shorter than the internal clock's cycle — the crew will suffer from 6 hours of jet lag. So the key point here is that jet lag after travelling westwards is less than after travelling eastwards. That's the relationship shown in Figure 11.4. Now, the method of dealing with this circadian dysrhythmia — that's the medical term for the disruption of our body's natural daily rhythms, what we commonly call jet lag — is a major research area in aviation. Because individual pilots react differently to time zone changes and resynchronise at different rates, there cannot be any hard and fast rules. Each individual must work out their own methods for dealing with the problem. However, there are some generally accepted techniques, and I want to walk you through them based on the length of the stopover. First, a short stopover of less than 24 hours. If the stopover is short with a rapid return to base, it may be advisable to try to maintain home time in your activities. For example, eating breakfast at home base time rather than conforming to local time, and sleeping at your normal home time hours. The idea is to avoid shifting your body clock at all, since you'll be back home soon. Second, a 24-hour stopover — and this is described as one of the most difficult intervals. A 24-hour stopover does not allow time for two good sleep periods, but it is too long a period to cover with only a single sleep session. The recommended approach may involve taking a limited rest period on arrival, so that at a later time your body will be more ready to sleep for a longer period before the call for duty. As the text notes, the options open are not easy. Third, for a stopover of more than 24 hours, the recommendation is to plan to readjust to the new local time as soon as possible. This means shifting your sleep and meal schedule to match the local time zone, rather than trying to maintain home time. So to summarise: westbound travel gives you a longer day and less jet lag; eastbound gives you a shorter day and more jet lag. For recovery, short stopovers mean stick to home time, 24-hour stopovers require careful planning of rest periods, and longer stopovers mean adapt to local time quickly.