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Fatigue & Flying


Flying can be terrifying when the pilot is tired. I recall one very sunny cloudless morning I woke up over the English Channel at 6000 feet over the blue still waters. I cannot recall how long I was asleep at the controls while the Shadow microlight, I thought I was in command of, was flying by itself. It must have been the late night before and the few days of touring in France with students and friends in a gaggle of 6 aircraft that caused the tiredness. The combination of the steady drone of the engine, the laminar air and the cool breeze coming through the air vent put me to sleep.

As we all might know Fatigue is cumulative, that’s why we all need holidays every week, every season, every year. In fact we need to rest after every few hours every day just to function normally. Sleep is the time when the body and mind is able rest and refresh for another day’s work or flying. A few hours of sleep daily, is akin to allowing the aircraft engine to cool down and refueling after a flight.

Normally we don’t mention fatigue affecting Private Pilots because they don’t have to fly if they don’t feel like it. It is another matter for Commercial Pilots as they are obliged to fly for work and to follow time schedules, across many time zones when their circadian rhythm is disturbed, causing loss of sleep.

The longer day light hours during the British Summer will reduce sleep hours because one wakes earlier with the sunshine and goes to bed late, as it turns dark later.

For instance, in London, the mid summer daylight hours are from 0340 till 2020 (17 hours 40 minutes of daylight) and the mid winter daylight hours are from 0810 till 1550 (7 hours and 40 minutes of day light), a difference of about 10 hours.

Private Pilots are as affected by tiredness and lack of sleep from their normal work schedules, as well as the stress caused at the work place. The daily commute to work can add up to quite a lot of time spent on the busy roads, with the potential to cause “road rage”.

Someone I know, collected his newly manufactured aircraft from the factory and flew it back to his home field. After a flight of about 8 hours, with several stops for food and fuel, during one long summer day, they crashed on the last landing and badly damaged the brand new aircraft, fortunately not sustaining any injuries themselves. I suspect the major cause of this “landing and subsequent crash” was cumulative fatigue and the desire to get home as soon as possible, combined with poor handling of the aircraft.

Fatigue and tiredness seriously deteriorates your decision making ability and can thus cause a crash due to the series of poor decisions taken in the most stressful parts of the flight; Take off and Landing.

In the pilot personal checks we tend to use the “IMSAFE” list, but not every pilot is diligent in applying it to themselves.

I have witnessed a friend of mine, a highly experienced flight instructor, make his final approach in his aircraft with which he was very familiar, in calm conditions, too high and too slow. He landed with a bang, bounced up and down a few times and finally came to a halt by the side of the runway with a bent aircraft. My friend and his new lady friend had not had enough sleep the previous 3 nights and this had led directly to delayed reactions on what should have been a normal approach to a normal uneventful landing.

We can describe Fatigue as a condition where capacity for work is reduced; efficiency of accomplishment is reduced; capacity to respond to stimulation is reduced and is accompanied by a feeling of weariness and tiredness.

Fatigue can be both physical tiredness and mental tiredness. Physical tiredness can cause discomfort or pain or cramp in a group of muscles, which can cause a very slow response or no response at all; resulting in a loss of control of aircraft.

There was one very memorable instance for me when a young energetic chap came for his first flight lesson one morning. I asked him, as I usually ask all my students, whether he had eaten breakfast; he hadn’t as he was on a fitness week with his wife and was on a diet. After about 15 minutes of flight, he started feeling nauseous, even though the air was calm. We quickly returned to the airfield and landed. He then mentioned he had been to the Gym early morning and was feeling very tired but was reluctant to admit this before take off. The combination of not eating properly and physical tiredness caused the nausea. Usually Hunger and Fatigue go hand in hand. The body and brain need sufficient fuel for flight, just like the aircraft does.

An unfit pilot will feel the effects of tiredness earlier than a fit pilot. Regular physical activity is required to build up stamina for work and similarly regular flight sessions are required to build up stamina for flying leading towards safer flights.

Mental tiredness can cause a feeling of lethargy, complacency and inability to perform normal tasks. When high intensity tasks and multiple tasks need to be performed, mental fatigue will cause loss of alertness and inability to respond correctly. For example I notice that after 40 minutes of a flight lesson, on occasion, some of my students turn left when I instruct them to turn right. This immediately tells me that I must terminate the training session and return to base and land.

Many flight students tell me they feel “drained of energy” and “completely exhausted” after a one-hour flight training session. This varies from person to person and depends on their individual circumstances, regardless of their fitness or age.

The Human Brain, even though a non-muscular, non-moving organ, is a high-energy consumption organ. Any intellectual or problem solving tasks, especially when learning to aviate whether on the ground or in flight, will consume energy and make one feel “brain-dead” after even a short time. The Brain consumes about 20% of the total energy needs of the human body. Much of this energy is used to fire the micro electrical currents between the millions of Neurons to process new information data.

Learning to fly involves a large amount of new information and stimulation and motion in 3 dimensions. This creates a lot of new visual, aural and problem solving data, which has to be processed and sorted, thus consuming much energy in a short time period. When resting, the brain consumes energy to re-organize the data and also to repair and regenerate brain cells. Thus healthy eating is essential for all pilots as well as good resting periods before and after flights, recharging your internal battery so to speak.

Many private pilots may not wish to acknowledge their mental or physical tiredness to their peers and passengers due to “loss of face” and may make the wrong decision to fly despite their anxiety, thus getting into more trouble in the air.

During this year’s unusually hot English summer where we have had 35 C temperatures, I felt the debilitating effects of heat-induced fatigue, especially during training flights in the aircraft with large clear windscreens. These allow the solar radiation to shine with full power on the body and cook you with ultra violet and infrared radiation. Wearing full sleeved white shirts and dark glasses reduced the heat a little bit and the small but powerful air vents kept one from over heating immediately in flight. But the few minutes on the ground whilst warming up the engine and performing pre take off checks, I found the most tiring and uncomfortable, leading me to cut short the time spent on ground.

A method to stay cool whilst on the ground is to maneuver the aircraft so that the sun is behind the cockpit rather than ahead; even though this may be not into the wind. (Thanks to the coolant stabilized Rotax engine; we don’t have to worry about “cold” seizures of the pistons). If you operate out of a grass strip, park the aircraft under the shade of a convenient tree when going through your pre take off checks.

Unusually, this summer has had a prolonged period of dry, hot weather in the UK due to the weakening of the jet stream. This was very good for my flight training work and I made the best of it while I could; however logging up more than 100 hours in about 30 days with daily flights, I could feel the fatigue build up. Long day light hours with an early sunrise, meant I could not sleep for more than 5 hours. Taking students flying in the middle of the day during hot temperatures and accepting flights after 6 pm in the evenings soon took its toll on my (60 years plus) body and brain.

After about 3 weeks, I reverted to a rhythm of flying only in the morning and evening and taking a break and siesta during the hot afternoons. This certainly averted poor decision-making due to cumulative fatigue. When operating my flight school in India, we flew early mornings from sunrise till about 10 am then broke off for ground school, lunch, siesta and did a couple of flights from 4 pm till sunset. This daily rhythm allowed for adequate rest periods despite the intense flying routine.

Many private pilots in the UK are allowed the privilege of a “self-declared” medical fitness to fly. I see this as a major disadvantage for the pilots as they may not realize that unchecked by a Doctor, they may be more likely to be affected by fatigue caused by some undetected underlying illness, especially if they are not as fit as they used to be or think themselves to be.

This article should be read in conjunction with my articles on “Flying in Turbulent Weather” and “Flying in Unusual Weather” available as iBooks.

Deepak Mahajan

August 2018

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