Human Performance & Limitations

The aircraft is only as safe as the person flying it. Human performance and limitations is about how your body and mind react to flight – altitude, motion, darkness, fatigue and pressure – and the habits that keep those weaknesses from turning into an accident. Most accidents involve human error, so this is one of the most practical subjects you will study.

1. The atmosphere and your body: hypoxia

Air is about 21% oxygen at every altitude, but the higher you go the lower the pressure, so each breath carries less oxygen into your blood. Too little oxygen is hypoxia. It is dangerous because it creeps up without pain: you feel fine, even confident, while your judgement fails.

• Early signs: slower thinking, poor judgement, euphoria, headache, tingling, blurred vision, blue lips and fingernails.
• Night vision suffers first – from as low as 5,000 ft.
• Smokers, tired or ill pilots and anyone after alcohol are affected lower down.

Time of useful consciousness

If oxygen is lost (for example a sudden decompression), this is roughly how long you can still act sensibly:

Altitude	Time of useful consciousness
18,000 ft	20–30 minutes
25,000 ft	3–5 minutes
30,000 ft	1–2 minutes
35,000 ft	30–60 seconds
40,000 ft	15–20 seconds

The cure is oxygen and descent. In an airliner the first action after a decompression is always oxygen masks on, then an emergency descent.

Hyperventilation

Breathing too fast – usually from stress or fear – washes carbon dioxide out of the blood. The symptoms (dizziness, tingling, muscle spasms) look like hypoxia. Slow, controlled breathing fixes it; if in doubt at altitude, treat it as hypoxia and use oxygen.

2. Pressure changes: ears, sinuses and gas

• The Eustachian tube connects the middle ear to the throat. Climbing, air escapes easily; descending, it may not get back in, causing pain. Swallow, yawn or use the Valsalva manoeuvre (pinch the nose and gently blow). Do not fly with a cold: a blocked ear or sinus can be very painful or burst an eardrum.
• Gas in the stomach and intestines expands as you climb.
• Decompression sickness ("the bends") comes from nitrogen bubbling out of the blood. After scuba diving, wait at least 12 hours before flying, and 24 hours after dives that needed decompression stops.

3. Vision

• The centre of the eye sees detail and colour (cones); the edges see movement and work in the dark (rods). Full dark adaptation takes about 30 minutes and one bright light ruins it – use dim red or white cockpit lighting.
• Every eye has a blind spot. Two eyes cover for each other, but a cockpit pillar can hide another aircraft. Move your head.
• Empty-field myopia: with nothing to focus on (haze, empty sky) the eyes relax to about 1–2 m and miss distant traffic.
• An aircraft on a collision course stays still in your windscreen and only grows at the last moment. Scan in small sectors of about 10°, pausing on each one.

Visual illusions on approach

Situation	It looks…	Risk
Runway narrower than you are used to	As if you are too high	Flying the approach too low
Runway wider than usual	As if you are too low	Flying too high, landing long
Runway sloping up	As if you are too high	Flying too low
Runway sloping down	As if you are too low	Flying too high
Night approach over dark ground or water ("black hole")	As if you are higher than you are	Descending into the ground short of the runway

The defence is the same each time: use the PAPI or VASI, the glideslope and your altimeter, not just your eyes.

4. Balance and spatial disorientation

The inner ear senses turning and acceleration, but it can be fooled – especially without a visible horizon.

• The leans: after a slow, unnoticed roll, levelling the wings feels like banking the other way.
• Somatogravic illusion: strong acceleration (for example a go-around) feels like pitching up; the pilot pushes forward towards the ground. Deceleration feels like pitching down.
• Graveyard spiral: in a long turn the sensation of turning fades; the pilot lets the nose drop and the spiral tightens.
• Coriolis effect: moving your head during a turn can cause a strong tumbling sensation.

In cloud or on a dark night, believe your instruments, not your body. VFR pilots should avoid flying into cloud at all – most loss-of-control accidents in poor weather start there.

5. Fitness to fly

Before every flight run the IMSAFE check:

• Illness – any symptoms?
• Medication – prescription or over-the-counter; many cause drowsiness.
• Stress – work, family, money.
• Alcohol – at least 8 hours "bottle to throttle", longer after heavy drinking; the EASA blood limit for pilots is 0.2 g/l.
• Fatigue – enough sleep? Fatigue affects judgement like alcohol.
• Eating and hydration – low blood sugar and dehydration (common in Middle-East heat) reduce performance.

Carbon monoxide from a leaking heater or exhaust is colourless and odourless and causes headaches, drowsiness and confusion. If you suspect it: heater off, fresh air in, land.

6. Information processing, stress and workload

• Short-term memory holds only about 5–9 items for a few seconds – that is why we write down clearances and use checklists.
• Performance is best at a moderate level of arousal: too little (boredom) or too much (overload, panic) and errors rise.
• Plan ahead to keep workload low in busy phases: brief the approach in the cruise, not on final.

7. Decision making and error

Good pilots make mistakes too – they catch them early. Two useful tools:

• DECIDE: Detect the problem, Estimate its importance, Choose an outcome, Identify actions, Do it, Evaluate the result.
• Threat and error management: spot threats (weather, terrain, fatigue, an unfamiliar airport) before they cause errors, and trap errors before they become undesired aircraft states.

Watch out for dangerous attitudes: anti-authority ("rules are for others"), impulsivity, invulnerability ("it won't happen to me"), macho and resignation ("nothing I can do"). And beware "get-there-itis" – pressing on into bad weather because you want to arrive.

Flying it at Levant

Fatigue and pressure are real in the simulator too: a long-haul flight at 3 a.m. invites mistakes. Use the checklists, brief each approach, use the PAPI on night arrivals into airports like Aqaba and Tabuk with dark desert around them, and do not be afraid to go around – a go-around is never a failure.

Check yourself

1. Which sense is affected by hypoxia first? Night vision.
2. How long should you wait to fly after a normal scuba dive? At least 12 hours (24 after decompression-stop dives).
3. The runway is narrower than you are used to. What illusion and risk? You seem too high, so you may fly the approach too low.
4. During a go-around you feel the nose pitching up strongly. What should you do? Trust the attitude indicator – it is probably the somatogravic illusion.
5. What does IMSAFE stand for? Illness, Medication, Stress, Alcohol, Fatigue, Eating.

Simulation training material based on standard PPL human performance theory. It is not medical advice.