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Pilots are supposed to be a pretty healthy lot, but even the finest human specimens have off days.

On these days, the safe pilot stays on the ground. Even though you may be an experienced pilot, flying with any sort of impairment must be avoided. Piloting requires rapid and frequent decision making and this means one must be feeling fit and well rested.

It is up to the individual to assess one's fitness to fly on any given day.

Do not fly if­

  • you are tired or feel weary.
  • you have a hangover.
  • you are drunk or drugged.
  • you are on any medication (consult your doctor).
  • you have a stomach upset or headache.
  • you have been to a dentist and had a local anaesthetic.
  • you have a lot on your mind.
  • you have a cold, cough or flu etc.
  • you are recovering from an illness.
  • you have had a concussion or accident causing shock (consult your doctor).

If there is the slightest doubt about your fitness, forget flying until you are better.

When on any medication, see your doctor and ask how you might be affected, and when you might be fit to fly again.



Human Factors is the term which broadly encompasses the study of human performance and limitations pertaining to operating an aircraft.

We have not evolved with the ability to fly. As a species we lack the physique, the physiology and a number of perception skills which are inherent in birds and other creatures which have evolved to fly. As aircraft have improved in reliability and ease of operation, the pilot has become an increasingly important component in aircraft accidents. Sadly, recent research has indicated that some 75% of aircraft accidents have significant human causal effect. Understanding our own human limitations is as important as knowing the limitations of the aircraft we fly.

Man evolved and adapted to a world which provides moderate temperatures, sea level atmosphere, a gravitational force of 1, good visual references and moderate speeds. If any of those conditions are disturbed the human being is placed in a potentially very hostile environment.

In the aviation environment we have to deal with a three dimensional world which is dynamic and at times requires a lot of ourselves as individuals to manage. That we can do this with comparative ease is not only due to aeroplanes which are relatively simple to operate, not only due to the sophistication of instruments and electronics, but also to the most important part of the equation - ourselves .

You have been, or are about to, be well trained in how to fly aeroplanes, and how to operate in the sky. And that learning will be on going for as long as you fly. Human Factors is about making sure that you are aware of your own physical and mental limits and how to manage them.

As pilots we require our machines to be in top order, our instruments to be reliable and accurate and such is the technology this is nearly always so. We also need to be in good order ourselves, and to understand some of the stresses (and how to deal with them) that are unique to going out and committing aviation.

We all have regular medicals, but what is presented to the clinician is only a snapshot of ourselves, and for most of us in the micro-lighting world our medical is a declaration with a general examination. All doctors will do more than that if you ask them. Get yourself checked out when you do your next medical. It's a comfortable feeling walking out of the surgery knowing all is well, and this is the common experience.

In the meantime, between medicals, what can we do to pre-flight the most important component - you? As a simple starter, before you pre-flight the aeroplane, run through the following check on yourself. Its simply called I'MSAFE: do it each time you fly. Be honest about it -

  • ILLNESS. Don't fly when you're ill. Even if its only a cold. All illnesses have the potential to cause visual and sense of balance problems. And give yourself suitable time to recover from an illness. Make sure you're fit. 'Do I have any symptoms?'
  • MEDICATION. Very few medications, including over the counter medications are designed with the pilot in mind. All medications have side-effects with drowsiness and suppression of primary senses being common. If your in doubt check it out. Your doctor, practice nurse, or chemist can tell you. And don't fly until you do. 'Have I been taking prescrtiption or over the counter drugs?'
  • STRESS. Its said and its very true that some stress in life is a good thing, but we know that there is an optimum amount, and we all know what its like if we exceed those very individual limits. Don't think that flying is a good stress-reliever - it is supposed to be relaxing, but you need to be able to operate if things become stressful in the cockpit, so, if its that bad, work it out somewhere else rather than in the air. 'Am I under pressure from the job? Do I have money, health or family problems?'
  • ALCOHOL or DRUGS. Both are especially bad news for judgement, decision making and balance. . Don't fly with a hangover - and if you smoke dope, choose another hobby. 'Have I been drinking with 8 hours? Within 24 hours?'
  • FATIGUE. All of us are aware of our degraded performance when we are tired. Flying can be very demanding. Make sure you are well rested. 'Am I tired or not adequately rested?'
  • EATING. Have a good breakfast before you fly. If your away on a x-country, take a bite to eat and take sufficient water. Altitude increases the rate of dehydration. And dehydration will impair judgement. 'Have I eaten enough of the proper foods to keep adequately nourished for the entire flight?'

We will not eradicate human error, but we can and should work towards managing it and reducing its negative consequences: Graham Wardell, CFI, Auckland Aero Club .

Normal human functions of vision, hearing, balance and orientation, respiration and mental capacity can all be adversely effected when we fly. In addition, we must cope with G forces, pressure changes, temperature changes, and humidity changes. Adverse medical factors such as alcohol, drugs, dehydration, hypoxia, disease and illness will also come into play.

The following explanations and strategies are discussed because when they are taken into account, they will enhance the pleasure we all get from going out to the airfield and safely committing aviation.


Good vision, both inside and outside the cockpit is obviously essential for safe flight. It tells us where we are going, where we have been and what is sharing our immediate airspace with us. It also plays a major role in balance and orientation. In fact our eyes provide about 80% of the orientation information received by the brain. Visual function requires about 30% of our oxygen requirements which may explain why this mechanism is so sensitive to hypoxia (lack of oxygen).

There are factors adversely affecting vision:

Blind spot - Small nerves behind the retina carry light stimulated nerve signals to the brain via the optic nerve, an area at the stalk of the eye where there are no light receptors. Any light falling on this area does not reach the visual centre of the brain. People generally are not aware of their blind spot, as the brain tends to fill in what it thinks should be there.

Time lag - The time lag in the visual process is very important when considering reaction times. Look out for pilots is not only a process of looking and seeing, but also a process of recognising, deciding and responding. Even in ideal conditions a time lag of up to 7 seconds may elapse between seeing and responding. How far can two converging aircraft travel in this time? The following two tables may provide food for thought.

PhaseResponseTimeTotal time
LookingIs there something out there?0.2 seconds0.2 seconds
SeeingYes indeed there is!0.3 seconds0.5 seconds
RecognisingIts another aircraft!!1.0 seconds1.5 seconds
EvaluatingAnd its coming this way!!!3.0 seconds4.5 seconds
RespondingManeuvering to avoid danger3.0 seconds7.5 seconds
At 120 knots closure they will travel towards each other 432 meters in 7 seconds
At 150 knots closure they will travel towards each other 540 meters in 7 seconds
At 180 knots closure they will travel towards each other 648 meters in 7 seconds

Scanning - Because of the way the human eye is structured, the area of acute visual perception for most of us is about a 20 degree cone around the retina, giving us a 20 degree arc of accurate vision. Because it takes about 1.5 seconds under normal circumstances for the process of looking, seeing and recognising to occur (glare and contrast factors can delay this process even further) we need to develop a scan that maximises our ability to keep a good lookout. Hence the development of the 20 degrees - 2 seconds rule. Divide the sky off into 20 degree segments and scan each for at least 2 seconds. You can apply the same rule to scan back in the cockpit.

If the view outside the cockpit is relatively unbroken by distinctive features, a type of short-sightedness can occur. This may happen when flying in hazy conditions, or over a smooth sea for example. This short-sightedness occurs because the eyes take up a relaxed state which causes them to be focused at a point 3 to 4 meters distance. You may think you are keeping a good lookout, but you are in fact focusing just outside the cockpit.! Empty visual field blindness can be overcome by periodically focusing on some distant feature, which will exercise the eye.

Effect of hypoxia (oxygen deprivation) on vision - As discussed the visual system requires about 30% of our oxygen requirements and is there fore extremely susceptible to oxygen deprivation . Sharpness of vision, colour perception, peripheral vision will all be affected.

The effect of g forces on vision - Pulling (positive) g will reduce blood flow and therefore oxygen supply to the brain. The pilot may notice loss of colour perception, loss of peripheral vision, blurring, and total loss of vision (black out). Black out is not the same as unconsciousness, but unconsciousness may quickly follow if the g force is maintained.

The effect of fatigue on vision - Our eyes are largely muscles which can be affected by fatigue. Although focusing is largely an automatic function, it still requires a certain amount of energy and the eyes can be among the first bodily function to become tired if the body is tired. We are all familiar with the need to rub, close and rest the eyes when we are tired. When we are tired, vision clearly suffers.

Canopies and vision - Think of your canopy as a visual aid - and treat it as if it were a good pair of sunglasses. Clean canopies are a delight, dirty or scratched ones are not. Clean the canopy inside and out before each flight with a non-abrasive cleaner and a soft lint free cloth. Wiping needs to be done vertically rather then horizontally.

Visual illusions - The visual system is not always accurate and can play tricks which can fool the unwary. We have already discussed the blind spot. A pilot in a cockpit with window and door frames needs to be aware that there is a tendency for the brain to fill in these gaps in vision without the pilot being aware of what is happening. We could be seeing a continuously empty sky, with that door frame hiding an approaching aircraft if it is in the pilots blind spot. Use the degrees - 2 seconds rule.

The brain is not always good at making visual comparisons, especially in conditions of poor viability, distracting line features and lack of familiar surrounding objects and features. A classic example is when a pilot familiar with trees of a certain height at his home field travels to a different area where the trees are smaller. The pilot will fly lower if he is judging airfield height by trees alone. Fatal accidents have been caused by this.


Respiration is the process of molecular exchange of oxygen and carbon dioxide within the body's tissues, from the lungs to cellular oxidation processes. The process is usually involuntary.

In the lungs are minute air sacs (about 300 million) called alveoli. The walls of the alveoli are very thin and semi-permeable. There is a pressure gradient across them which allows oxygen to pass into the bloodstream via very fine capillaries, and carbon dioxide to come out of solution in the blood and into the alveoli where it is then exhaled. The oxygen is able to combine with haemoglobin in the blood and is then transported to every cell in the body. The air we breath is a combination of gases comprising 78% nitrogen, 21% oxygen and 1% other gases . Nitrogen plays no part in respiration. Respiration depends entirely on the amount of available oxygen.

The ratio of oxygen to other gases remains constant at the altitudes we fly but pressure reduces with altitude. It is a general rule that total pressure of air has halved by 18000 feet and halved again by 34000 feet. The actual amount of oxygen available reduces with altitude in the same proportion as the other gases.

Dalton's Law of Partial Pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases.

So, how much oxygen do we need? The standard atmosphere assumes a sea-level pressure of 1013.25 millibars, or 14.7 psi, or 760 mm of mercury (Hg). The partial pressure of oxygen at sea-level is approximately 150mmHg. Once inhaled, this partial pressure of oxygen is further reduced because of the continual presence of CO2 and water vapour in the lungs. Thus, 102 mm Hg is the required partial pressure of oxygen in the lungs for normal functioning, and any major reduction of this pressure will have adverse consequences.

As we ascend in the atmosphere, the quantity and pressure of oxygen available is reduced below the required 102mm Hg. Adverse effects of this reduction are not especially noticeable below 8000 feet, but can become critical above 10000 feet. Above 10000 feet we must have supplemental oxygen available.

The legal requirement is as follows : During any time an aircraft is being operated between 10000 feet and 13000 feet AMSL for a period of more than 30 minutes, or above 13000 feet AMSL, each crew member and each passenger must use supplemental oxygen. Any passengers carried when supplemental oxygen is required must have been briefed on the normal and emergency use of the oxygen equipment used. The Civil Aviation Rules prescribe detailed requirements for the type of oxygen and equipment to be used, and for its use.

General symptoms of hypoxia include:

  • euphoria
  • target fixation
  • personality changes
  • loss of judgement
  • 'fuzziness'
  • amnesia
  • lethargy
  • confusion
  • heat/cold sensitivity
  • cyanosis (blueing of extremities)
  • unconsciousness
  • death

Visual symptoms of hypoxia include:

  • decrease in colour perception
  • decrease in peripheral awareness
  • decrease in visual acuity.

Neuro Muscular symptoms of hypoxia include:

  • clumsiness
  • fine tremor
  • speech slurring
  • slow movements

There are two very important and rather sobering aspects of hypoxia that should make pilots especially wary: The insidious effects of hypoxia and the time of useful consciousness. Although its not usual for micro lights to fly much above 10000 feet, it is reported that it is increasingly common for them to do so. The following table may be of interest:

Time of useful consciousness
Altitude (feet)SittingModerate Activity
1800020-30 minutes10-15 minutes
2100010 minutes5 minutes
250003 minutes2 minutes
300001.25 minutes45 seconds

Factors influencing onset, intensity and tolerance of hypoxia - Altitude attained, rate of ascent, time at altitude, physical activity, ambient temp., illness, fatigue, drugs/alcohol, smoking, stress/workload level of fitness.

Action in the event of suspecting hypoxia -

  1. Go on to oxygen and select full flow (beware the Oxygen Paradox - next)
  2. Check oxygen system for leaks, kinks and contents.
  3. Reduce power, extend flaps and trim aircraft for maximum descent rate.
  4. Get below 10000 feet
  5. Report what is happening.
  6. Unless absolutely sure why the problem occurred, return and land.
  7. In returning, be cautious ; you will be fatigued by the incident so don't rush and DO listen to advice from the ground.

If you suspect hypoxia in a pilot in an other aircraft, get them to do the above: talk slowly - they may not be aware they are hypoxic and reluctant to listen - if they can hear at all. And watch from a safe distance - they will have visual problems!

Oxygen Paradox - This is a temporary worsening of symptoms when oxygen is restored to someone who is hypoxic. It is caused by a reflex which constricts momentarily the arteries to the brain. The danger is that you may feel worse momentarily when you first go on oxygen, you then suspect it isn't working and turn it off!!

Common causes of Oxygen deficiency include not using supplemental oxygen when its required, failure to turn on the system, poor fitting masks, mask removal, system failure. If your going to fly at these kinds of altitudes, PRE-FLIGHT THE OXYGEN SYSTEM JUST LIKE YOU WOULD THE AIRCRAFT!!

Hyperventilation is a condition where an abnormal increase in the breathing rate results in an excess loss of CO2 which in turn raises the alkalinity of the blood. This pH change causes a number of adverse effects :

  • Rapid pulse
  • Feelings of unreality
  • dizziness or faintness
  • tightness of the chest
  • Numbness or tingling in the hands, feet and around the mouth
  • increased anxiety
  • clumsiness and tremors
  • fainting in severe cases
  • feelings of shortness of breath

Causes of hyperventilation include

  • excessive worry or anxiety
  • pain
  • loud noise
  • vibration
  • heat
  • motion sickness
  • hypoxia
  • G loading

Treatment of hyperventilation -

  • Encourage deep and slow breathing (12 - 16 breaths per minute).
  • Use oxygen if available
  • Be reassuring
  • Re-breathing (cup hands or use a bag)
  • Do not hold your breath!!

Remember, hyperventilation may be a symptom of hypoxia, but this is unlikely at lower altitudes (below 10000 feet). A person who is hyperventilating will not be harmed by breathing 100% oxygen whereas telling a person who is hypoxic to slow their breathing could kill them.


As we climb and gain altitude, atmospheric pressure continuously decreases. According to Boyle's Law, at a constant temperature if the pressure of a gas is halved, its volume will double. The opposite is so on descent. There are several areas in the body where gas is trapped , for example the stomach and the gut, the middle ear, the sinuses, and the teeth. As these gases expand and contract with altitude changes, they can cause some issues.

Stomach and gut - These areas seldom cause problems as there is ample room for the gases to expand. However, some may feel discomfort. The rule here is simple - Flex, Airate, Relax, Tell. And then smile!

Middle ear - Gas trapped in this area usually escapes through the Eustachian tubes (tubes which connect between the middle ear and the throat, which enable the pressure in the middle ear to be equalised). Those tubes could well be blocked if you have a cold or the flu. Ear pain on descent is common, uncomfortable and can have serious implications. Clear the Eustachian tubes by swallowing, moving your jaw or using the Valsalva Manoeuvre (pinch the nose, tilt the head back slightly and momentarily pressurise the throat by forcing air up from the lungs, causing the ears to pop). Sudden descents with blocked Eustachian tubes can cause damaged eardrums, permanent hearing impairment and inner ear infections.

Sinuses - these can cause pain on ascent if the sinuses are blocked. Normal rates of ascent shouldn't cause problems. Flying with a cold is not recommended because of the difficulty you will have clearing your ears and sinuses.

Teeth - Tiny pockets of air under fillings etc will expand and may even cause fillings to dislodge. Pain will normally be relieved on landing. Take some pain relief and go visit your dentist.

Nitrogen and the bends

As we have already discussed, nitrogen makes up about 80% of the earths atmosphere. Although not required for respiration, it may be found in solution in the bloodstream as well as organs. Normally these dissolved gases don#t pose a problem for pilots below 10,000 ft. Prolonged high altitude flight however can allow the dissolved nitrogen to come out of solution, form small bubbles which are then free to move about the body. A serious attack can cause serious and permanent problems.

Symptoms include :

  • Joint pain
  • Itchiness
  • Numbness
  • Tingling
  • Paralysis of parts of the body
  • Poor co-ordination and movement
  • Mental confusion
  • Visual disorders
  • Inner ear problems
  • Shortness of breath
  • Tight or painful chest
  • Painful coughing
  • Unconsciousness

So why are we discussing an issue which is well known in the scuba diving community? Very few of us fly above 10, 000 ft. But some of us fly as well as dive, and pilots flying too soon after a dive are especially susceptible. A good rule is to allow at least 24 hours between the last dive and flying, and if your dive has exceeded 35 meters depth, 48 hours would be wise. The bends is a serious medical emergency and urgent compression in a recompression chamber is imperative. And if you happen to be flying the patient to medical assistance, do not fly above 500ft AMSL. Doing so will SERIOUSLY aggravate the condition.


Orientation is essentially the ability to know which way is up, and where we are positioned relative to the sky and the ground. This a largely automatic process which we take for granted. At least 80% of the orientation information is provided by vision with the rest provided by movement sensors in the body. In conditions of 1g, at slow speeds , we can easily confirm our position or orientation by visual reference.

In flying however, things can be quite different. We may have poor visual references. We may be trying to cope with a wide range of speeds and accelerations. Things can and do go awry.

The visual system - The importance of the visual system cannot be over-emphasised. It is as important in flying as it is on the ground. As pilots, we are taught from our first lesson to fly an aircraft by relating its attitude relative to the horizon.

The balance organs - These comprise of two main organs: the Semicircular Canals and the Otolith Organs. Both are contained in the inner ear.

The semicircular canals are three fluid filled tubes mounted at right angles to one another so as to sense accelerations in 3 planes of movement. Once the acceleration has stopped they will cease to sense it. A steady state turn may therefore not be detected. Although sensitive, the canals have a threshold to cut out minor accelerations. Problems can occur where these sub-threshold accelerations are suddenly detected or if they are misinterpreted. An extreme example might be where a pilot in cloud or at night believes himself to be in a dive with wings level, but in fact the aircraft is in a dive with bank. The turn is completely undetected, and if the pilot attempts to pull out of the dive with elevator only, matters are made worse. This particular situation has sadly killed many pilots - John Kennedy Jnr being amongst them.

The Otolith Organs sense both tilt and longitudinal acceleration. They can give erroneous information and in particular they can misinterpret a forwards acceleration as a steep climb with severe consequences if a pilot attempts to correct a steep climb that is not there, near the ground.

We also have a nervous system which detects pressure on the body, stretch and body position. An example is pressure on the buttocks when sitting. Remember however that the body without visual reference cannot distinguish between a +3G loop and a +3g turn.

Persons on the ground will not often become disorientated as all 3 balance and orientation systems tend to work together to confirm the information that each is passing to the brain. In the air however there is a high potential for confusing and conflicting information to be passed to the brain and if we try to rely on seat of the pants or the feel of things# without proper training, the results can be catastrophic.

  • Stay in visual conditions unless you can fly on instruments.
  • You will have less than 180 seconds before you will loose control.
  • Micro light Aircraft are not permitted to fly either at night or in cloud under any circumstances.
  • This is why.

There are two other manifestations of disorientation - flicker vertigo and motion sickness distracting and if prolonged can cause a person to feel dizzy and quite unwell. Re-position the aircraft to avoid the effect.

Motion Sickness is caused by prolonged (also sudden) unaccustomed motion of the body which upsets the orientation system. Motion sickness can be aggravated by anxiety and low cockpit activity. And it tends to be more common among passengers and trainee pilots than amongst the experienced. For trainee pilots, gain air experience as soon as possible. This will reduce both the anxiety while increasing confidence levels. Keep fit, rest well and eat sensibly before flying. Instructors: allow the student to do as much of the flying as possible - this will do much to reduce the chances of motion sickness occurring

Passengers should be given warning of any manoeuvres and unnecessary manoeuvres should be avoided. And if it happens, might I suggest that bi-carbonate of soda in a bucket of water is probably as effective as any of the commercial cleaners. Stow a suitable disposable bag in the cockpit for those less than smooth days.


Exposure to high environmental temperatures is clearly the most common cause of overheating or heat stress. Breathing dry air, or oxygen, may exacerbate this along with wind, exertion, dehydration and fatigue. The prevention of heat stress and its related condition, dehydration, is particularly important for pilots especially pilots involved in long cross-country flights.

Heatstroke occurs when the body's internal temperature control system becomes stressed. The body responds by increasing blood flow to the skin, which then uses sweat glands to produce moisture which cools the body by a process of evaporation. In extreme conditions of temperature and/or humidity, the body may have difficulty dissipating enough heat by these methods, and internal temperatures can rise to dangerous levels.

Mild episodes may produce little more than a headache, cramps or a rash. If allowed to continue, or to worsen, hallucinations and collapse may result. In the case of severe dehydration, the body may stop sweating in which case you are also dealing with a serious medical emergency which requires immediate medical attention.

Dehydration is related to heat stress and may share many of the same symptoms. Essentially, you need to ingest between 250-300 mls/hr simply to cover fluids lost by respiration. 5-600 mls/hr is recommended, especially on hot days. Carry water in the aeroplane with you when you are going on a cross country. Drink plenty of fluids and avoid diuretics (fluids which make you pee) such as coffee.

All the aircraft in my club have transparencies in their roofs (one doesn't actually have a roof). Wear suitable head wear. Wear loose fitting clothing which will allow some air to circulate around your body.

Ensure the body is well watered and fit. And for those of you who do long duration flights, remember that there have been emergency landings made in such haste that bladders have ruptured and major medical emergencies have happened. Carry a suitable receptacle. What goes in does go out. Lets all ensure its via the normal route.

Symptoms of heat stress:

  • Heat rash
  • Muscle cramps
  • Headache
  • Nausea (and vomiting)
  • Dryness of mouth, eyes and nose
  • Poor coordination
  • Poor concentration
  • Drowsiness
  • Weakness
  • Lethargy
  • Slurred speech
  • Confusion
  • Hallucination

Overcooling This is just as much as a problem as overheating. The direct cause is low environmental temperatures. Contributing factors include:

  • Insufficient correct clothing (greatest heat lose occurs through the head)
  • Hypoxia
  • Fatigue
  • Food - not enough or the wrong kind
  • Anxiety
  • Injury
  • Recent illness
  • Wind
  • Wet clothing

Symptoms include: uncontrolled shivering, tiredness, clumsiness, irrational behaviour, lack of energy etc. For those of us in the Trike/open cockpit world, be sensible. The wind chill factor is extreme. Remember that cases of frostbite requiring amputations have been recorded following open cockpit flights.


It is very difficult to define the ideal pilot personality. Sadly, its far easier to define what makes a bad pilot, as these are the folk who usually end up in the accident statistics. Fortunately modern aviation psychological testing as applied by air forces is able to throw some light on the process, and give some rules of thumb, and these #rules# are as applicable to sport aviation clubs as they are to the military. Its important for each of us to understand the role that pilot personality can have in aviation safety practices

Reckless and erratic personalities generally do not make good pilots. Bad pilots are over-confident, slapdash, impulsive, careless, complacent, dogmatic, arrogant, inaccurate, and rough on aircraft/equipment. All good pilots should be alert for bad pilots, who will require close watching and special attention if they are to continue flying and become good pilots.

Good pilots, on the other hand display good airmanship at all times. Airmanship may be defined as the display of good common sense, good practice and high standards in the air. Good pilots not only have good flying skills, but also personality traits which if not innate, can be learned and developed. Good pilots# stay out of trouble. Generally, they do not have incidents or accidents which are a result of bad decision making or faulty decisions.

The aviation environment can be demanding physically and psychologically, and attitudes to safety, pilot personality, human learning mechanisms, human capacity and workload may all play a part in the safety equation.

Mental capacity

When a person is learning a new skill, mental workload is high and the brain may be working at nearly full capacity. Residual capacity for making decisions or handling new tasks and emergencies may be low. As an individual becomes more experienced (and tasks become more automated), residual mental capacity is increased, allowing more accuracy as well as better decision making.

Mental performance suffers when the brain becomes overloaded with information or activity. Interestingly, if mental activity is too low, mental performance also suffers.

Stress and Fatigue

Stress is defined as the non-specific response of a human to any demand for change. These demands can be real or imagined - the stress on the body is the same.

Some stress is not only normal but essential - our bodies are built for it, and it is a normal part of life. We tend to enjoy different levels of stimulation at different times and if a good balance is maintained, few individuals have problems with stress.

Many folk however struggle to maintain that balance and its important for us in sport aviation to understand the symptoms and signs of stress which take us beyond our normal levels and degrade our performance and therefore effect our safety.

The two main types of stressors are direct and indirect. Direct stress in our sport comes from the immediate task of flying the aircraft. It may arise from such things as weather, turbulence, mechanical issues, navigational issues , personal fitness (including fatigue, hypoxia, dehydration etc). Indirect stress usually relates to issues to do with ones own personal environment - families, relationships, finance etc.

As long as your abilities as a pilot are greater than the demands flying places on you, the less of a problem stress will be . But if demand exceeds abilities, the chances of an accident becomes quite high.

Responses to the stressed state include:

  • Forgetting important tasks
  • Becoming short tempered
  • Noisy of uncharacteristic behaviour
  • Substance abuse (including alcohol)
  • Relationship problems
  • Flying dangerously or unsafely

More direct symptoms while flying may include nervousness or shaking, sweating, anxiety, non-typical behaviour and hyperventilation. Prolonged acute stress can have long term medical consequences including peptic ulcers and cardio-vascular problems.

Coping with Stress.

The best ways of reducing stress and its effects are to:

  • Keep physically fit and healthy
  • Eat well
  • Rest, relax and sleep well
  • Know you capabilities and stay within them
  • Think and plan ahead
  • Get organised and prioritise and avoid procrastinating
  • Seek assistance
  • Understand stress and how it effects you! And then do something about it.

Fatigue can be defined as the accumulation of unresolved stress perhaps building up over a period of time. It is debilitating and a fatigued pilot will be unable to fly safely. The symptoms of fatigue are similar to being excessively stressed and can be difficult to recognise in ourselves until quite advanced. Don't take pride in your ability to hack it - all you are doing is placing yourself and others at unnecessary risk. Remember, fatigue cannot be resolved quickly. It will only be resolved by resolving the workload/stress issues and by getting adequate sleep and rest. Stress management techniques, time management, better prioritisation, improved physical fitness and better quality sleep will help. Do something about it - but not in the air.

Operational Pitfalls

An FAA analysis many accidents has identified of classic behavioural traps pilots can fall into. Those particularly pertinent to microlight flying include:

  • Peer Pressure Poor decision making based on an emotional response to peers rather than evaluating a situation objectively.
  • Mind set The inability to recognise and cope with changes in the situation different from those anticipated or planned.
  • Get-There-Itis This tendency, common among pilots, clouds the vision and impairs judgement by causing a fixation on the original goal or destination with a total disregard for any alternative course of action.
  • Scud Running Pushing the capabilities of the pilot and the aircraft to the limits by trying to maintain visual contact with the terrain while trying to avoid physical contact with it.
  • VFR into IMC Continuing visual flight into instrument conditions often leads to spatial disorientation or collision with ground or obstacles. It is even more dangerous if the pilot is not instrument rated.
  • Getting Behind the Aircraft Allowing events or the situation to control your actions rather than the other way round. Characterised by a constant state of surprise at what happens next.
  • Loss of Positional or Situational Awareness Another case of getting behind the aircraft which results in not knowing where you are, an inability to recognise deteriorating circumstances, and/or the misjudgement of the rate of deterioration.
  • Flying Outside the Envelope Unjustified reliance on the (usually mistaken) belief that aircraft's capability meets the demands imposed by the pilot's (usually overestimated) flying skills.
  • Neglect of Flight Planning, Pre-Flight, Checklists Unjustified reliance on the pilot's short and long term memory, regular flying skills, repetitive and familiar routes, etc.

Hazardous attitudes that influence pilot decision making

  • Anti-authority- The rules do not apply to me. Found in people who do not like others telling them what to do. They may be resentful of advice from others, and may regard rules, procedures and regulation as silly or unnecessary.
  • Impulsivity- I must act now! The need to do something-anything-immediately. They do not stop to think, and select the best alternative. They do the first thing that comes to mind.
  • Invulnerability- It won't happen to me. These people believe that accidents happen to others, and never really feel or believe that they nay be personally involved. These pilots are more likely to take chances and increase risk.
  • Macho- I'll show you how good I am. Pilots with this attitude will try to prove themselves by taking risks to impress others.
  • Resignation- I must stick to the plan, I can't change things. If your number is up- it's up. This pilot will leave the actions and decisions to others, and may go along with unreasonable requests just to be a nice guy.
  • Deference- It must be OK if you say so. Typical in a student/instructor relationship or in group flying, where one senior pilot makes decisions based on his skill and experience, and others follow along into situations outside of their abilities.
  • Denial- It is not as bad as it looks or they say. Based on belief or hope rather than hard facts.
  • Get-home-itis- I have to get there! Often because of promises made to others for flights, appointments, etc. Also if no options have been thought out- no Plan B.

For each of these attitudes there is an antidote...

  • Anti-authority- The rules do apply to me. Most are safety oriented and are safe minimums learned from the wisdom and experience of others.
  • Impulsivity- Don't rush- take a few seconds or minutes to think the situation through . Do your planning, do your checks. Don't be pushed or hurried by others.
  • Invulnerability- It can happen to me. I am not bullet-proof.
  • Macho- I don't need to show off to impress others. Professionalism in aviation is what counts and lasts.
  • Resignation- I can make a difference. I have the knowledge and training to make a difference. It is important to have a Plan B, and maybe a Plan C... and use them when necessary.
  • Deference- Make and act on the decisions you are comfortable with. Make these clear to others. Fly within your competencies and skills as pilot-in-command.
  • Denial- If it looks bad- it probably is. Do not downplay the significance of flight relevant information just because it conflicts with your goals or intentions.
  • Get-home-itis- Do not get cornered by your commitments, those of others, or timelines that dictate that you must fly. This often leads to an early appointment- with death or disaster.


Our cardio-vascular system is designed to perform at its best at a G force of 1. It is quite a complex system and is particularly susceptible to changes in G.

In an aircraft which is pulling G (the gravity value is greater than 1), the blood in the pilots head tends to be forced downwards towards the stomach and the legs. This reduces the blood flow, and therefore the oxygen flow to the brain. Up to about 2.5 G, the body can compensate, although this may take several seconds. Beyond 2.5 G however, so much blood is being drained from the brain that the pilot will progressively experience loss of colour perception, loss of peripheral vision, vision blurring, total loss of vision and ultimately loss of consciousness. All of these functions will be restored however upon the restoration of conditions of 2.5 G or preferably less.

In negative g conditions, we are even less tolerant. We may suffer a type of congestion where its difficult for blood to flow back to the heart. Oxygen availability to the brain and eyes is just as compromised as if there was insufficient blood pressure. Pilots describe red out - a condition probably caused by pooling of blood around the eyelids.

Sustained negative G is difficult to achieve in a micro light, so we are not often confronted with this issue. Most aircraft are designed for much less negative G than positive G. Always comply with the operating limits of the aircraft you are flying.


Drugs and Alcohol

Operating any aircraft while under the influence of any mood, perception or performance altering drug will have a serious and damaging effect on any pilots performance. This effect may last for many hours after consumption and should never be underestimated. This not only includes opiates, cannabis, methamphetamines, and LSD but also alcohol.

While the primary effects of alcohol are well known, what is not generally well known is that even though blood alcohol levels may have returned to zero, most people are unaware that their performance can be seriously impaired by the less-known after effects such as nausea, headache and fatigue. Even low to moderate use can seriously jeopardise the safety of a flight the following morning.

Effects of alcohol

  • Poor performance generally
  • Disorientation
  • Dehydration
  • Increased susceptibility to G forces
  • Increased susceptibility to hypoxia
  • Increased susceptibility to the bends
  • Interference with the temperature regulation of the body

Alcohol will seriously degrade a pilots performance. Even small amounts. A study once demonstrated that even after achieving a achieving a blood alcohol level of 0.01%, pilots flying a simulator had a procedural error rate of 68%.

The immediate effects of alcohol will impair sight, balance and seat of the pants feel. Alcohol literally dilutes the fluid in the Semi-Circular Canals, meaning that with any sudden head movement, dizziness and nausea are often experienced due to these fluids travelling further and faster than they would normally. This results in exaggerated signals being sent to the brain, which can be extremely disorientating on the ground, let alone in the air.

Associated with this is the Coriolis phenomenon which is a severe tumbling sensation bought on by moving the head out of the plane of rotation, simultaneously stimulating one set of semi-circular canals while deactivating another. Very modest amounts of alcohol can induce this effect . Both of these effects can persist in some individuals for several days after blood alcohol levels have returned to zero.

Nystagmus affects the visual system and can be described as a series of eye movements caused by stimulation of the semi-circular canals. Nystagmus can be induced by spin recovery manoeuvres, and amplified in severity and duration if there is alcohol in the system. Pilots suffering from Nystagmus find it extremely difficult to focus either on the instrument panel or on the world outside. The disorientation is very marked and can quickly lead to total loss of control of the aircraft.. Nystagmus can be demonstrated up to 11 hours following the intake of even modest amounts of alcohol.

The hangover

The hangover syndrome can last up to 48 hours depending on how much the individual has consumed. General feelings of ill-health including headache, nausea, gastrointestinal disturbances etc will impair mental ability and seriously degrade your performance as a pilot.

Alcohol related fatigue

Alcohol is widely used as an aid to sleep. The problem with this is that it interferes with normal sleep patterns and provides poor quality sleep (either lack of, or no REM sleep). This results in feelings of tiredness and impaired concentration. A nightcap before retiring may cause increased tiredness the next morning.

The news is not all bad however. The body metabolises alcohol quite quickly (at the rate of 1 standard drink per hour) so enjoy alcohol consumed with your evening meal - just allow time for your blood alcohol level to drop. The ideal target is zero at lights out.

Alcohol has many side-effects including dehydration, which will allow the excessive excretion of electrolytes, minerals and salts. It will also reduce G force tolerance partly by vasodilation as well as the dehydrating effect which decreases blood volume. Alcohol is also known to impair the metabolism and utilisation of oxygen increasing your vulnerability to hypoxia.

Alcohol has a number of persistent effects that can negatively impact on safety in flight. There are significant problems flying during the hangover phase, and even flying the next morning after a few drinks may not be the wisest option. Adherence to a simple bottle to throttle rule does not guarantee maximum performance in the air. In some cases for some individuals this may mean not flying at all the morning after the night before.

'''CAA rules state:

  • No operating an aircraft if your capacity may be impaired by the effects of drugs and/or alcohol.
  • No passenger who is under the influence of drugs and/or alcohol is to be carried.'''

Minor Illnesses

As stated, it is not recommended to fly with either a cold or the flu. Hay fever similarly will cause congestion, although you can use steroidal nasal sprays to help clear the sinuses (don't use anti-histamine pills - they will make you drowsy and inattentive - despite the assurances of the manufacturers).

Where a pilot has had a major illness, accident or operation which necessitates recovery in hospital and at home, its clear that the person should take a rest from flying until recovery and good health are regained.

What is not quite so clear is what to do when the illness has been of a less serious nature eg colds, influenza, bronchitis, headache, menstrual problems, diarrhea etc. Use common sense. Remember take-offs are optional, landings aren't.

There may be occasions where the day starts well but we get tired or unwell. This will undermine your performance and you won't learn when you're like this. Speak up if you are dual - your instructor will take your mind off it while returning to land. Carry an air sickness bag just in case and remember - many have been there and done that, so don't be embarrassed.