Human performance

C. Haemoglobin in the red blood cells

Oxygen binds to haemoglobin in the red cells as blood passes the alveoli. That is also why carbon monoxide is so dangerous: it grabs haemoglobin far more readily than oxygen does.

B. Hyperventilation

Anxiety-driven over-breathing gives dizziness, tingling, and a racing heart. At low altitude hypoxia is unlikely, so assume hyperventilation and slow your breathing down.

A. Cumulonimbus (Cb)

The correct answer is: Cumulonimbus (Cb).

A. Descending with a cold (blocked Eustachian tube)

On descent the middle ear must take air in through the Eustachian tube. A cold blocks it, so descent is the dangerous direction. Do not fly if you cannot clear your ears.

A. Breathing in excess of the body's needs (over-breathing)

Hyperventilation is over-breathing: ventilating the lungs more than the body needs. The usual cause is anxiety or stress, and good training is the best defence.

A. Nitrogen coming out of solution as bubbles in the body

Henry's law: nitrogen dissolved in the body at higher pressure comes out as bubbles when the pressure drops quickly - the bends, the chokes and nervous-system symptoms.

A. 21 %

The percentage stays about 21 % throughout the lower atmosphere. What falls with height is the pressure, so each breath contains less oxygen.

B. Carbon dioxide in the blood

The respiratory centre responds mainly to carbon dioxide. That is why hyperventilation, which washes CO2 out, confuses the breathing drive.

B. Too little carbon dioxide in the blood

Over-breathing washes carbon dioxide out of the blood and the blood becomes alkaline. Breathing into a paper bag brings the CO2 level back up, and the brain slows the breathing.

B. As altitude increases

Higher means lower air pressure, so lower oxygen partial pressure, even though the air is still about 21 % oxygen. The higher you go, the faster hypoxia sets in.

A. Euphoria

Hypoxia may start with a feeling of well-being - euphoria - so the pilot is often the last person to suspect anything. Cyanosis and convulsions come later.

C. It is present in cigarette smoke

Cigarette smoke contains carbon monoxide, which binds to haemoglobin over 200 times more readily than oxygen. Every cigarette takes part of your oxygen-carrying capacity out of use for hours.

A. 78 % nitrogen, 21 % oxygen, 0.93 % argon

Nitrogen 78.08 %, oxygen 20.95 %, argon 0.93 %, then traces of carbon dioxide and other gases. Water vapour varies and is counted separately.

B. 18,000 ft

About 18,000 ft for half, and about 36,000 ft for a quarter. The oxygen available falls in the same proportion.

A. 1.98 °C per 1000 ft

1.98 °C per 1000 ft (6.5 °C per km) up to the tropopause at 36,090 ft, where the temperature settles at -56.5 °C.

A. 120/80 mmHg

About 120 over 80: systolic 120 mmHg as the heart contracts, diastolic 80 mmHg as it relaxes and refills.

C. A decrease in heart rate

Hyperventilation speeds the heart up - it does not slow it. Dizziness and tingling are classic symptoms.

A. The time during which a pilot can still take proper corrective and protective action after the oxygen supply is interrupted

TUC is useful time, not time to unconsciousness. After it ends, a pilot may still be awake for a few seconds but can no longer act effectively - so the mask goes on first.

A. Feel too high and fly a shallower approach than normal

Haze makes the runway look further away, so the pilot thinks he is high, reduces the descent and flies shallow - and risks landing short.

A. Rods, in the periphery of the retina

Rods sit in the periphery, see only black and white, and work in low light; cones are central and give colour and detail by day. At night, look slightly off-centre.

C. Both stagnant and anaemic hypoxia

There are four types: hypoxic (altitude), anaemic (reduced oxygen-carrying capacity), stagnant or ischaemic (poor blood flow) and histotoxic (cells cannot use the oxygen).

B. A deficiency of oxygen in the body tissues, enough to impair their function

Hypoxia is oxygen deprivation of the body's tissues, the brain first. For pilots the main cause is breathing air at low pressure at altitude. Excess nitrogen coming out of solution is decompression sickness.

A. Put on oxygen masks, then begin an emergency descent

Oxygen first - time of useful consciousness may be only seconds. Then an emergency descent to about 10,000 ft, where everyone can breathe without supplementary oxygen.

A. 7,000 ft

A non-smoker typically meets hypoxia symptoms around 10,000 ft; a smoker can meet them around 7,000 ft - a 3,000 ft penalty.

C. Liveware is the hub, so the non-human components should be adapted and matched to it

The human (liveware) sits at the centre of the SHEL model. Software, hardware, environment and other people are matched to the human - not the other way round.

A. Vestibular system of the inner ear

The vestibular apparatus of the inner ear tells you which way is up. Without a visual horizon it is easily fooled, and that is spatial disorientation.

B. The percentage of oxygen stays about 21 %, but air density and oxygen partial pressure fall

The mix stays the same - about 21 % oxygen - but the air gets thinner, so the partial pressure of oxygen falls. That drop in partial pressure is what causes altitude hypoxia.

A. Anxiety or stress

Anxiety, fear and stress. A thorough briefing calms passengers, and good training prevents it in pilots.

A. Consciously slow the breathing rate to about 10-12 breaths a minute, without breathing deeply

First check the oxygen in case it is hypoxia. If the symptoms persist, slow the breathing to 10-12 breaths a minute and avoid deep breaths.

A. Decompression sickness (the bends)

Joint pain is the bends - nitrogen coming out of solution in the tissues. Other forms are the chokes, skin manifestations and nervous-system symptoms.

A. The total pressure of a gas mixture equals the sum of the partial pressures of its gases

Dalton: total pressure = sum of partial pressures. This is why oxygen falls with altitude even though it stays at 21 %. The other options are Boyle's law and Henry's law.

B. Vision (eyesight)

Eyesight is primary; the balance organs of the inner ear are a secondary system. That is why losing the visual horizon leads to disorientation.

A. A loss of airspeed and climb performance

Losing headwind costs indicated airspeed and performance straight away - the microburst trap after the initial headwind has made the climb look good.

A. Vitamin A deficiency and carbon monoxide from smoking

Night vision suffers from a lack of vitamin A, from carbon monoxide inhaled while smoking, from cabin altitudes above 5000 ft and from long exposure to bright sunlight. Closing one eye in bright light is the trick that preserves it.

A. May be delayed and appear several hours after the exposure, even after landing

Nitrogen bubbles do not always form at once. Symptoms - bends, chokes, skin manifestations, neurological symptoms, circulatory shock - may appear several hours after the exposure, so a pilot who feels fine on landing is not necessarily clear.

B. Oxygen and carbon dioxide

The body takes in oxygen and gives off carbon dioxide, and the CO2 level drives breathing. Nitrogen matters in decompression sickness, not in normal gas exchange.

A. Been scuba diving with compressed air shortly before the flight

Diving with compressed air loads the body with extra nitrogen. Fly soon afterwards and even a modest drop in pressure can release it as bubbles - hence the rule not to fly for 24 hours after diving to 30 ft or more.

B. 5-8 %

A pack a day takes away about 5-8 % of oxygen-carrying capacity, because carbon monoxide ties up haemoglobin. It also raises the risk of carbon monoxide poisoning.

A. Decreases

Almost all water vapour is in the lowest few kilometres, because cold air holds far less. Air at cruise levels is very dry, which is why dehydration is a real issue on long flights.

A. 4572 m

FL150 is 15,000 ft, and 15,000 x 0.3048 = 4572 m.

A. Medulla of the brain

The respiratory centre is in the medulla. It works automatically, driven mainly by the level of carbon dioxide in the blood, and you can override it only to a limited extent.

B. 60-80 beats per minute

About 60 to 80 beats per minute; the usual reference value is 72. At rest the heart then pumps about 5 litres a minute.

A. 30 to 60 seconds

About 33-54 seconds at 35,000 ft, roughly halved at 40,000 ft - and halved again by a rapid decompression.

A. Fill with fog (mist), dust and debris

The sudden drop in pressure and temperature forms fog, and dust and debris fly about. The crew may be briefly dazed, which slows donning the masks.

A. The autokinetic effect

Autokinesis: with no other references, a fixed light seems to wander. Keep your eyes moving and cross-check the instruments.

B. An optimum (moderate) level of arousal

Performance peaks in the middle of the arousal curve. Too little brings boredom and missed information; too much narrows attention.

A. Loss of the eye's ability to focus on near objects, due to the lens stiffening with age

Presbyopia comes with age: the lens stiffens and near focus is lost. It is corrected with reading or bifocal lenses.

A. Expand

Boyle's law: gas volume grows as pressure falls. Gut gas can roughly double by 18,000 ft cabin altitude, causing pain.

A. Equalises the pressure in the middle ear with the outside (cabin) pressure

The Eustachian tube links the middle ear to the throat so that its pressure can equalise with the cabin. If it is blocked - a cold is the usual cause - descent is when the ear hurts, because air cannot get back in.

A. Three tiny bones - the ossicles

The ossicles - malleus, incus and stapes - form a small lever system that turns the vibration of the eardrum into movement at the inner ear. The Eustachian tube only equalises pressure, and the semicircular canals sense rotation.

A. Tensing the leg and abdominal muscles (anti-G straining)

Under +Gz the blood drains away from the head, bringing grey-out, then black-out, then G-LOC. Tensing the lower body raises the arterial pressure and keeps blood in the brain a little longer.

A. Visual disturbances, lack of concentration, euphoria

Hypoxia sneaks up on you: night vision goes first, reasoning and concentration slip, and a feeling of well-being - euphoria - hides the danger. Barotitis is an ear problem and hypothermia is cold.

A. Cones, concentrated in the fovea

The fovea is all cones - it gives the sharpest day vision and colour, and no night vision at all. The rods, spread around the periphery, take over in dim light.

A. The creeps

Bends in the joints, chokes in the lungs, creeps under the skin - a crawling sensation. The leans is a vestibular illusion, nothing to do with nitrogen.

A. 1 to 2 minutes

TUC falls fast with height: about 3-5 minutes at FL250, 1-2 minutes at FL300, 30 seconds to 1 minute at FL350. Moving about shortens it further.

A. It shows no apparent relative motion - it stays at a constant bearing

A target on a collision course sits still on the windscreen at a constant bearing, growing only slowly until the last seconds. That lack of movement is exactly why it is the hardest to see.

A. Diffusion

Gas exchange in the lungs is diffusion across the respiratory membrane: oxygen into the blood, carbon dioxide out of it, each moving from higher to lower partial pressure.

A. 20 Hz to 20 kHz

A young, healthy ear hears from about 20 Hz to 20,000 Hz. Prolonged exposure above 80-90 dB causes permanent hearing loss.