Every heavy transport aircraft has over a hundred gauges and lights that quantify the aircraft's performance. But what about the crew's performance? One of the most important factors in a safe and effective mission is FATIGUE. It shows up as the inability to react physically and mentally to cues inside and outside the aircraft. Approximately 80% of post-accident investigations have identified human factors as a cause of the mishap and, as the following chart illustrates, the majority of accidents.
That last 15% of the flight typically arrives at the end of a 10 to 12 hour crew day. The crew has spent about eight hours seated in a dry, noisy, confined aircraft at a cabin altitude of 6000 feet. Their body rhythms are at their lowest ebb (between 0300 and 0600 hours departure base local time). In addition, the trip is often conducted through the night and into the morning with a glaring dose of rising sun just to enhance that "sand in the eyeballs" effect.
Like hypoxia, fatigue is insidious and every crew member must recognize the symptoms. The aircraft commander must be acutely aware not only of his own fatigue but that of the entire crew. The most visible clue is a change in behaviour. Most people can probably describe the "who" they change into when they're tired. Unfortunately, this change doesn't always head in the same direction. That congenial, co-operative sort of fellow can run the behavioural gamut from becoming positively comatose to a testy, monosyllabic person you wouldn't trust with anything sharper than a Flight Comment magazine. In effect, fatigue becomes a mood altering drug that no flight surgeon would prescribe. Fortunately, there are things aircrew can do to counter the effects of fatigue on their minds and bodies and the mission.
Fatigue is primarily due to a lack or disruption of normal sleep patterns but it can be mitigated through proper pre-flight rest. To gear up for a night mission, a nap is in order. It isn't easy to snooze from 1300 to 1600 while the rest of the world is going about mowing lawns or building a new deck right outside your bedroom window. Foam earplugs and a sleeping mask can help. So does an understanding mate who can field phone calls and intercept the kid's enroute to your room to show you a new toy. Studies have shown that the average sleep cycle runs about ninety minutes with the beneficial REM state at the end of this period. If you can, try multiples of this and if you wake up with less than ninety minutes remaining; walk, run or play with aforementioned new toy.
All long haul drivers have their own enroute maintenance techniques and should continue with what works best for them. Current research indicates that small snacks rich in complex carbohydrates (fruit, salad and grains) are beneficial. Coffee and tea are initially stimulating but, being diuretics; they eventually rob the body of water. Drinking water or fruit juice instead will reduce this problem and help counteract the dry cabin air. A few minutes of stretching or isometrics are also worthwhile. Such actions assist the movement of blood out of the lower body back to the head. Performed regularly, or at least once prior to the top of descent, will help keep that tired ol'body alert for the last 15% of the flight. The cobwebs are sometimes difficult to shake, though, as performance during this time period (0300 – 0600 hrs local time at the departure base) has been estimated to be at the same level as someone having a blood alcohol level of .09%. Incidentally, that would provoke an impaired driving charge in most provinces.
Normally, getting eight hours of sleep after a flight is not a problem. However, if scheduled ground time between missions is 24 hours the benefits of that sleep will be wearing thin by departure time. Your departure will be, once again, smack in the middle of your biorhythmic low. "High to Low, lookout below..."
Fatigue can, and does, accumulate, not only throughout each mission, but also from flying several missions over a certain period of time. Each day (and night) brings increasingly challenging demands to perform safely. Cockpit discipline and professionalism will help but, with a biorhythmic clock that's gone digital, aircrew must learn to gauge their fatigue to ensure performance levels remain within safe parameters.
This article was first published in 1990 - Issue 4 of Flight Comment. This issue as well as all other issues of Flight Comment can be viewed on the DFS website.