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PPL Human Performance and Limitations study materials
PPL Human Performance and Limitations study resources

PPL Human Performance and Limitations practice questions

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Question 1Human Factors: Basic Concepts and Aviation Physiology

At sea level, the partial pressure of oxygen in dry air is approximately 159 mmHg. What is the approximate partial pressure of oxygen in the alveoli of a healthy adult breathing air at sea level?

  1. About 46 mmHg
  2. About 100 mmHg Correct answer.
  3. About 159 mmHg
  4. About 40 mmHg

Explanation

Inspired oxygen is diluted by water vapour in the airways and by carbon dioxide in the alveoli, so alveolar PO2 falls to roughly 100 mmHg. The alveolar gas equation (PIO2 minus PaCO2/R) predicts this value closely in a healthy adult.

Question 2Human Factors: Basic Concepts and Aviation Physiology

A pilot climbs rapidly to 12,500 ft without supplemental oxygen. Which physiological change best explains the resulting impairment in night vision and colour discrimination?

  1. Reduced arterial oxygen partial pressure lowering retinal function Correct answer.
  2. Increased middle-ear pressure distorting the visual field
  3. Rising blood alcohol concentration from dehydration
  4. Increased carbon dioxide retention depressing the retina

Explanation

The retina, particularly the rods used for dim-light vision, has a high oxygen demand and is very sensitive to falling arterial oxygen partial pressure. Hypoxia therefore degrades night vision and colour discrimination early, before more obvious symptoms appear.

Question 3Human Factors: Basic Concepts and Aviation Physiology

Which statement correctly describes the time of useful consciousness for a healthy pilot breathing ambient air at 25,000 ft?

  1. About 30 minutes
  2. About 3 to 5 minutes Correct answer.
  3. About 1 to 2 minutes
  4. About 15 to 20 seconds

Explanation

At 25,000 ft the time of useful consciousness in fit young subjects is typically around 3 to 5 minutes. It falls steeply with further altitude, reaching roughly 15 to 20 seconds at 40,000 ft.

Question 4Human Factors: Basic Concepts and Aviation Physiology

A pilot breathes 100% oxygen from a mask before a rapid decompression to 40,000 ft. What is the main physiological benefit of this pre-breathing?

  1. It lowers the risk of decompression sickness
  2. It increases the oxygen-carrying capacity of the blood
  3. It maintains oxygen saturation during the ascent Correct answer.
  4. It washes nitrogen out of body tissues

Explanation

Pre-breathing 100% oxygen denitrogenates the lungs and blood, so that after a sudden decompression the pilot's arterial oxygen saturation is preserved long enough to don an oxygen mask or descend. It does not change haemoglobin content or the oxygen-carrying capacity.

Question 5Human Factors: Basic Concepts and Aviation Physiology

Which of the following best defines the term 'hypoxia' as used in aviation physiology?

  1. An excessive volume of oxygen in the alveoli
  2. A reduced concentration of carbon dioxide in the blood
  3. A failure of the lungs to eliminate nitrogen
  4. An inadequate supply of oxygen to body tissues Correct answer.

Explanation

Hypoxia is a deficiency of oxygen at the tissue level, whether caused by reduced oxygen partial pressure, impaired transport or impaired utilisation. It is distinct from hyperventilation, which lowers carbon dioxide.

Question 6Human Factors: Basic Concepts and Aviation Physiology

During a slow ascent to altitude, a pilot shows cyanosis, a slow pulse and drowsiness rather than the expected rapid breathing. Which pattern of hypoxia does this most suggest?

  1. Histotoxic hypoxia
  2. Stagnant hypoxia
  3. Hypoxic hypoxia Correct answer.
  4. Hypemic hypoxia

Explanation

Hypoxic hypoxia from reduced alveolar oxygen partial pressure typically produces cyanosis, tachycardia and impaired judgement, but a slow pulse and drowsiness can occur as decompensation develops. The setting of exposure to reduced oxygen partial pressure points to hypoxic hypoxia rather than the other three categories.

Question 7Human Factors: Basic Concepts and Aviation Physiology

A pilot hyperventilates during a stressful approach while breathing normally pressurised cabin air. Which set of symptoms is most likely?

  1. Warmth, bradycardia and deep sleep
  2. Dizziness, tingling in the fingers and muscle cramps Correct answer.
  3. Cyanosis, cough and blood-stained sputum
  4. Chest pain radiating to the left arm

Explanation

Hyperventilation lowers arterial carbon dioxide, producing hypocapnia with light-headedness, paraesthesia of the extremities and carpopedal spasm. Recognising these symptoms helps distinguish hyperventilation from hypoxia, although the two can coexist.

Question 8Human Factors: Basic Concepts and Aviation Physiology

Why is smoking before a flight of particular concern for a pilot operating at altitude?

  1. It raises the carbon monoxide level and reduces oxygen transport Correct answer.
  2. It lowers the body's requirement for oxygen
  3. It increases the rate of nitrogen absorption
  4. It increases the oxygen-carrying capacity of the blood

Explanation

Smoking raises carboxyhaemoglobin, which reduces the amount of haemoglobin available to carry oxygen and shifts the dissociation curve. This makes the pilot more susceptible to hypoxia at altitude.

Question 9Human Factors: Basic Concepts and Aviation Physiology

Which physiological mechanism is primarily responsible for the reduced oxygen saturation observed in a healthy pilot during prolonged exposure to a low cabin altitude?

  1. An increase in haemoglobin concentration
  2. A decrease in alveolar oxygen partial pressure Correct answer.
  3. A decrease in the oxygen affinity of haemoglobin
  4. A decrease in the diffusion capacity of the lungs

Explanation

At altitude the reduced barometric pressure lowers the inspired and therefore alveolar oxygen partial pressure, which drives down arterial saturation. The other mechanisms either do not occur acutely or are compensatory rather than causative.

Question 10Human Factors: Basic Concepts and Aviation Physiology

A pilot flying at 8,000 ft cabin altitude develops a headache and fatigue. Which of the following is the most appropriate first action?

  1. Increase cabin altitude to reduce pressure
  2. Continue the flight and monitor symptoms
  3. Descend to a lower altitude and use supplemental oxygen Correct answer.
  4. Reduce the rate of breathing to conserve oxygen

Explanation

Early symptoms of hypoxia should be treated by descending and, if available, using supplemental oxygen. Continuing exposure allows symptoms to worsen and judgement to deteriorate.

Question 11Human Factors: Basic Concepts and Aviation Physiology

Which statement about the oxygen-haemoglobin dissociation curve is correct?

  1. A shift to the right increases the release of oxygen to the tissues Correct answer.
  2. Carbon dioxide decreases the release of oxygen to tissues
  3. A shift to the left increases oxygen release at the tissues
  4. The curve is linear over the physiological range

Explanation

A rightward shift, caused by increased carbon dioxide, acidosis or raised temperature, reduces haemoglobin affinity and increases oxygen unloading to tissues. This is the Bohr effect.

Question 12Human Factors: Basic Concepts and Aviation Physiology

A pilot flying at 30,000 ft with a pressurised cabin at 8,000 ft experiences a rapid decompression. What is the most immediate hazard?

  1. A decrease in noise level
  2. A rapid fall in oxygen partial pressure Correct answer.
  3. A sudden increase in cabin temperature
  4. An increase in cabin humidity

Explanation

Rapid decompression causes an almost instantaneous drop in oxygen partial pressure, which can produce hypoxia within seconds at high altitude. The pilot must don the oxygen mask immediately.

Question 13Human Factors: Basic Concepts and Aviation Physiology

Which of the following best describes the concept of 'time of useful consciousness' (TUC)?

  1. The time required to don an oxygen mask
  2. The time a pilot can hold their breath at altitude
  3. The period from exposure to hypoxia until the ability to act is lost Correct answer.
  4. The time from loss of oxygen supply until death occurs

Explanation

TUC is the interval between exposure to a hypoxic environment and the point at which the pilot can no longer take effective protective action. It is shorter at higher altitudes and is reduced by exertion or cold.

Question 14Human Factors: Basic Concepts and Aviation Physiology

A pilot with a mild head cold is considering flying in a pressurised aircraft. Which concern is most relevant from a physiological standpoint?

  1. Reduced risk of decompression sickness
  2. Increased risk of barotrauma to the ears and sinuses Correct answer.
  3. Decreased susceptibility to hypoxia
  4. Improved oxygenation at altitude

Explanation

A cold can block the Eustachian tubes and sinus ostia, so pressure changes during ascent and descent cannot equalise, risking barotrauma. The other options are not physiological consequences of a cold.

Question 15Human Factors: Basic Concepts and Aviation Physiology

Which of the following is a recognised symptom of decompression sickness?

  1. Improved coordination
  2. Joint pain and skin itching Correct answer.
  3. Bradycardia and hypotension
  4. Increased visual acuity

Explanation

Decompression sickness results from nitrogen bubbles forming in tissues and blood, producing joint pain, skin itching or mottling and, in severe cases, neurological or respiratory symptoms. Prompt descent and oxygen are indicated.

Question 16Human Factors: Basic Concepts and Aviation Physiology

A pilot is exposed to a cabin altitude of 40,000 ft after a decompression. Which action should be taken first?

  1. Don the oxygen mask and select 100% oxygen Correct answer.
  2. Inform air traffic control of the situation
  3. Check the cabin pressure gauge
  4. Initiate a descent to 10,000 ft

Explanation

At 40,000 ft the time of useful consciousness is very short, so the immediate priority is to don the oxygen mask and select 100% oxygen. Descent and communication follow once oxygen is secured.

Question 17Human Factors: Basic Concepts and Aviation Physiology

Which of the following best explains why the body's oxygen consumption remains relatively constant during exposure to altitude?

  1. The respiratory rate falls to conserve oxygen
  2. The heart rate decreases to conserve oxygen
  3. Haemoglobin concentration increases immediately
  4. Tissues continue to require the same energy production Correct answer.

Explanation

Metabolic demand at the tissue level does not fall simply because altitude rises, so oxygen consumption remains broadly constant while supply is reduced. Compensatory increases in heart rate and breathing attempt to maintain delivery.

Question 18Human Factors: Basic Concepts and Aviation Physiology

Which statement about the effects of positive 'g' on the cardiovascular system is correct?

  1. Oxygen saturation rises because of increased lung perfusion
  2. Heart rate falls sharply and blood pressure rises
  3. Blood is displaced towards the feet, reducing cerebral perfusion Correct answer.
  4. Blood is displaced towards the head, raising cerebral perfusion

Explanation

Positive g displaces blood towards the lower body, reducing venous return and cerebral perfusion, which can lead to grey-out or g-LOC. Countermeasures include the anti-g straining manoeuvre and g-suits.

Question 19Human Factors: Basic Concepts and Aviation Physiology

A pilot performing a high-g manoeuvre begins to experience tunnel vision. What is the most appropriate immediate response?

  1. Relax the anti-g straining manoeuvre and breathe normally
  2. Increase the rate of the turn to complete the manoeuvre quickly
  3. Perform the anti-g straining manoeuvre and reduce g load Correct answer.
  4. Lean forward to improve blood flow to the brain

Explanation

Tunnel vision is an early sign of reduced cerebral perfusion from positive g. Performing the anti-g straining manoeuvre and reducing the g load restores blood flow to the brain and prevents loss of consciousness.

Question 20Human Factors: Basic Concepts and Aviation Physiology

Which of the following is a correct description of spatial disorientation in aviation?

  1. A temporary loss of consciousness caused by hypoxia
  2. A correct perception of the aircraft's attitude
  3. A failure of the aircraft's navigation systems
  4. An incorrect perception of the aircraft's position or motion Correct answer.

Explanation

Spatial disorientation is a mismatch between the pilot's perception of the aircraft's attitude or motion and reality, usually arising from misleading vestibular or visual cues. It is a significant cause of accidents in poor visual conditions.

Question 21Human Factors: Basic Concepts and Aviation Physiology

During a sustained constant-rate turn without visual reference, a pilot may feel that the aircraft is straight and level. Which sensory system is primarily responsible for this illusion?

  1. The semicircular canals Correct answer.
  2. The proprioceptive system
  3. The visual system
  4. The otolith organs

Explanation

The semicircular canals respond to angular acceleration but adapt to a sustained constant-rate turn, so the pilot no longer perceives the turn. This 'leans' illusion is a classic cause of spatial disorientation.

Question 22Human Factors: Basic Concepts and Aviation Physiology

Which of the following best describes the 'somatogravic illusion'?

  1. A false sensation of pitch during linear acceleration Correct answer.
  2. A false sensation of roll during a descent
  3. A false sensation of yaw during a climb
  4. A false sensation of rotation during a constant turn

Explanation

The somatogravic illusion occurs when linear acceleration is misinterpreted by the otolith organs as a pitch change, leading the pilot to believe the aircraft is climbing when it is accelerating. It is particularly dangerous during take-off or go-around in poor visibility.

Question 23Human Factors: Basic Concepts and Aviation Physiology

Which of the following is the most reliable defence against spatial disorientation?

  1. Trusting the flight instruments and maintaining proficiency in their use Correct answer.
  2. Relying on bodily sensations to confirm attitude
  3. Increasing the rate of head movements to improve orientation
  4. Flying only in visual meteorological conditions

Explanation

Because the vestibular system can give false information, the pilot must rely on flight instruments and maintain instrument flying proficiency. Bodily sensations are unreliable in the absence of visual references.

Question 24Human Factors: Basic Concepts and Aviation Physiology

Which statement about night vision and the eye is correct?

  1. Rods are more sensitive in dim light but do not detect colour Correct answer.
  2. Cones adapt more slowly than rods to darkness
  3. Rods are concentrated in the fovea and provide colour vision
  4. Cones are more sensitive than rods in dim light

Explanation

Rods are highly sensitive to low light but do not mediate colour vision, while cones provide colour and detail but require higher light levels. Dark adaptation takes about 30 minutes and is impaired by smoking and hypoxia.

Question 25Human Factors: Basic Concepts and Aviation Physiology

A pilot is taking a medication that causes drowsiness. According to basic aviation human factors principles, what is the most appropriate course of action?

  1. Fly only short sectors to limit exposure
  2. Fly with another pilot who can monitor the situation
  3. Consult the AME or medical authority before flying Correct answer.
  4. Reduce the dose to half and fly

Explanation

Medications that impair alertness can degrade performance and judgement, so the pilot should seek advice from an aeromedical examiner or authority before flying. Self-adjusting the dose or relying on another pilot does not remove the risk.

Question 26Human Factors: Basic Concepts and Aviation Physiology

Which statement best describes the role of the autonomic nervous system in a pilot's response to a sudden, startling event such as an engine failure warning?

  1. Both branches act only on skeletal muscle and have no effect on heart rate or blood pressure.
  2. The parasympathetic branch increases heart rate and blood pressure while the sympathetic branch promotes digestion and recovery.
  3. The autonomic nervous system controls voluntary movement and conscious decision-making during the emergency.
  4. The sympathetic branch increases heart rate and blood pressure while the parasympathetic branch promotes digestion and recovery. Correct answer.

Explanation

The autonomic nervous system regulates involuntary functions and has two divisions with largely opposing actions. Sympathetic activation prepares the body for action by raising heart rate, blood pressure and breathing rate, while parasympathetic activity dominates during rest and supports digestion and recovery. Understanding this balance helps explain why arousal can sharpen alertness yet degrade fine motor control and judgement.

Question 27Human Factors: Basic Concepts and Aviation Physiology

A pilot reports feeling alert and capable of flying after 18 hours awake, but performance testing shows slowed reactions and poor concentration. Which human factors concept best explains this discrepancy?

  1. The pilot's performance is normal because reaction time is preserved during sleep loss.
  2. Fatigue only affects physical strength and leaves mental performance unaffected.
  3. Subjective alertness is an unreliable indicator of actual cognitive impairment from fatigue. Correct answer.
  4. The pilot has developed tolerance to fatigue and can safely extend the duty period.

Explanation

Fatigue degrades cognitive performance, vigilance and reaction time before the individual reliably notices the decline. Because self-assessment of alertness is poorly correlated with measured performance, pilots may feel fit while actually impaired. This is why flight time limitations and fatigue risk management rely on objective duty records rather than self-report alone.

Question 28Human Factors: Basic Concepts and Aviation Physiology

Which statement correctly describes the function of the Eustachian tube during a descent in a pressurised aircraft?

  1. It equalises pressure between the middle ear and the cabin by allowing air to pass into the middle ear. Correct answer.
  2. It drains fluid from the middle ear and has no role in pressure equalisation.
  3. It equalises pressure only when the aircraft is climbing, not when descending.
  4. It seals the middle ear completely during descent to protect the eardrum from pressure change.

Explanation

The Eustachian tube connects the middle ear to the nasopharynx and normally opens during swallowing or yawning to equalise pressure. On descent, cabin pressure rises and air must flow into the middle ear to prevent the eardrum from being pushed inward. If the tube is blocked by a cold or congestion, the resulting pressure difference causes pain and can damage the eardrum.

Question 29Human Factors: Basic Concepts and Aviation Physiology

A pilot is about to fly after an overnight duty that ended only six hours before the report time. Which consideration is most relevant to human performance?

  1. Fatigue is only relevant for long-haul operations and can be ignored for short sectors.
  2. The pilot should drink coffee to fully restore performance before flight.
  3. Short sleep opportunity reduces recovery, so fatigue-related impairment is likely even if the pilot feels rested. Correct answer.
  4. Six hours of rest is always sufficient because sleep needs are identical for all adults.

Explanation

A reduced sleep opportunity before duty limits recovery and increases the likelihood of fatigue-related impairment. Individual sleep needs vary, and subjective feelings of rest do not guarantee adequate recovery. Caffeine may mask drowsiness but does not reverse the underlying cognitive deficit, so fatigue management should address sleep opportunity and duty scheduling.

Question 30Human Factors: Basic Concepts and Aviation Physiology

Which statement about the effects of alcohol on a pilot's performance is most accurate for aviation human factors?

  1. Alcohol's effects are fully eliminated once the pilot feels sober again.
  2. Moderate alcohol intake improves reaction time by reducing stress.
  3. Alcohol affects only motor skills and leaves decision-making intact.
  4. Alcohol impairs judgement, coordination and vigilance, and these effects can persist after blood alcohol returns to zero. Correct answer.

Explanation

Alcohol is a central nervous system depressant that degrades judgement, coordination, vigilance and information processing. Residual effects such as hangover and disturbed sleep can impair performance even after blood alcohol concentration has fallen. This is why regulations specify minimum bottle-to-throttle intervals rather than relying on subjective sobriety.

Question 31Human Factors: Basic Concepts and Aviation Physiology

A pilot flying a long sector at night complains of dry eyes, headaches and difficulty focusing on instruments. Which factor most directly explains these symptoms?

  1. Excessive oxygen partial pressure in the cabin.
  2. Increased carbon dioxide from the aircraft's air conditioning system.
  3. Reduced cabin pressure causing hypoxia at cruise altitude.
  4. Low cabin humidity combined with prolonged visual concentration on close instruments. Correct answer.

Explanation

Cabin air at altitude is very dry, and prolonged focusing on nearby instruments increases the demand on the eyes and reduces blink rate. Together these cause dry eyes, headaches and difficulty focusing. Managing hydration, humidity and visual rest breaks helps reduce these symptoms, which are common in long sectors.

Question 32Human Factors: Basic Concepts and Aviation Physiology

Which statement best describes the concept of situational awareness in aviation?

  1. It is the pilot's ability to recall checklist items from memory.
  2. It is the aircraft's automated system for detecting traffic conflicts.
  3. It is the pilot's physical fitness level before flight.
  4. It is the perception and understanding of relevant elements in the environment and the projection of their future status. Correct answer.

Explanation

Situational awareness has three levels: perceiving relevant information, comprehending its meaning, and projecting how it will develop. Loss of situational awareness often precedes errors and is a major contributor to accidents. It depends on attention management and is not the same as memorising procedures or relying on automation.

Question 33Human Factors: Basic Concepts and Aviation Physiology

A crew notices that both pilots are focusing on a single instrument fault while the aircraft drifts off the assigned altitude. Which human factors phenomenon best explains this?

  1. Fixation or attention tunnelling, where attention is locked onto one element at the expense of the overall picture. Correct answer.
  2. Channel capacity, where the crew can process all information simultaneously without error.
  3. Habituation, where repeated exposure reduces sensitivity to a stimulus.
  4. Complacency, where the crew ignores all instruments because they trust automation.

Explanation

Fixation, or attention tunnelling, occurs when attention becomes locked onto one task or instrument so that other relevant information is missed. This narrows situational awareness and can allow deviations such as altitude loss to go unnoticed. Effective scanning and cross-monitoring are defences against this phenomenon.

Question 34Human Factors: Basic Concepts and Aviation Physiology

A pilot begins to experience tunnel vision and a grey haze during a sustained high-g turn. Which action is most appropriate?

  1. Lean forward and hold the breath without muscle tension.
  2. Increase the rate of turn to complete the manoeuvre quickly.
  3. Perform the anti-g straining manoeuvre, ensure the g-suit is functioning and reduce 'g' load. Correct answer.
  4. Relax the anti-g straining manoeuvre and breathe rapidly.

Explanation

Tunnel vision and greyout are early signs of reduced cerebral blood flow under positive 'g'. The correct response is to perform the anti-g straining manoeuvre, confirm the g-suit is operating and reduce the 'g' load before consciousness is lost. Ignoring these warning signs risks G-LOC.

Question 35Human Factors: Basic Concepts and Aviation Physiology

Which of the following best describes the function of the vestibular system in orientation?

  1. It provides information about linear acceleration and rotation through the semicircular canals and otolith organs. Correct answer.
  2. It provides reliable information about orientation in all flight conditions.
  3. It detects visual motion only and has no role in balance.
  4. It measures barometric pressure to inform the pilot of altitude.

Explanation

The vestibular system detects angular acceleration through the semicircular canals and linear acceleration and gravity through the otolith organs. In flight, these signals can conflict with visual information and produce illusions. The system is not reliable for orientation without visual reference.

Question 36Human Factors: Basic Concepts and Aviation Physiology

A pilot accelerating in a level attitude during takeoff feels a strong sensation of pitching up. Which illusion is most likely?

  1. The Coriolis illusion, caused by a head movement during a turn.
  2. The autokinetic illusion, caused by a stationary light in darkness.
  3. The leans, caused by a prolonged constant turn.
  4. The somatogravic illusion, where linear acceleration is misinterpreted as a pitch-up. Correct answer.

Explanation

The somatogravic illusion occurs when sustained linear acceleration stimulates the otolith organs in a way that is interpreted as a change in pitch. During takeoff this can create a false sensation of pitching up and lead a pilot to push forward. Recognising the illusion and relying on instruments is essential.

Question 37Human Factors: Basic Concepts and Aviation Physiology

Which statement about the eye's photoreceptors is correct for night vision?

  1. Cones are responsible for detecting dim lights in the periphery.
  2. Rods provide sharp colour vision in the fovea during daylight.
  3. Cones are most sensitive to low light and provide colour vision at night.
  4. Rods are more sensitive to low light and are concentrated in the peripheral retina. Correct answer.

Explanation

Rods are highly sensitive to low light and are concentrated in the peripheral retina, which is why off-centre viewing improves detection of dim objects at night. Cones provide colour and sharp detail but require higher light levels. This distribution explains why scanning away from a dim object can make it easier to see.

Question 38Human Factors: Basic Concepts and Aviation Physiology

A pilot is flying with a head cold and is scheduled for a descent into a high-pressure airport. Which consideration is most relevant?

  1. Congestion can block the Eustachian tube and prevent equalisation, causing ear pain and possible damage. Correct answer.
  2. The cold will improve pressure equalisation by increasing mucus flow.
  3. The cold only affects the nose and has no effect on the ears.
  4. Flying with a cold is safe if the pilot uses decongestant medication.

Explanation

A cold can cause swelling and congestion that block the Eustachian tube, preventing pressure equalisation during descent. This can lead to ear pain, barotrauma and even eardrum damage. Pilots should consider fitness to fly, and medication use must be evaluated for its own effects.

Question 39Human Factors: Basic Concepts and Aviation Physiology

Which statement about the effects of carbon monoxide on a pilot is correct?

  1. Carbon monoxide binds to haemoglobin more readily than oxygen, reducing oxygen transport. Correct answer.
  2. Carbon monoxide has no effect on haemoglobin and is harmless at low concentrations.
  3. Carbon monoxide affects only the lungs and does not impair cognitive function.
  4. Carbon monoxide increases oxygen delivery to tissues by improving haemoglobin affinity.

Explanation

Carbon monoxide binds to haemoglobin with much greater affinity than oxygen, forming carboxyhaemoglobin and reducing the blood's oxygen-carrying capacity. Symptoms include headache, dizziness and impaired judgement, and they can occur at concentrations that are not obvious. In aviation, sources include exhaust leaks from cabin heating systems, and detection is important.

Question 40Human Factors: Basic Concepts and Aviation Physiology

A pilot has been breathing oxygen through a mask at high cabin altitude and then removes the mask at 10,000 ft cabin pressure altitude. Which statement best explains why the pilot's blood oxygen saturation falls only gradually rather than instantly?

  1. The body stores a reserve of oxygen in the blood and tissues that is consumed over the following minutes Correct answer.
  2. The lungs continue to extract sufficient oxygen from the reduced partial pressure at 10,000 ft
  3. The carotid bodies delay their response to falling arterial oxygen until hypoxia is severe
  4. Carbon dioxide in the blood is converted to oxygen by the enzyme carbonic anhydrase

Explanation

Time of useful consciousness after sudden loss of oxygen supply is governed largely by the oxygen already carried in the blood and tissues, so saturation declines progressively rather than immediately. This is why the effective performance time at 10,000 ft is measured in minutes rather than seconds, and why the pilot still has a limited window to don the mask again.

Question 41Basic Aviation Physiology and Health Maintenance

At what approximate altitude does the partial pressure of oxygen in the alveoli first fall to a level where a healthy resting pilot's oxygen saturation begins to decline noticeably without supplemental oxygen?

  1. Around 18,000 ft
  2. Around 25,000 ft
  3. Around 5,000 ft
  4. Around 10,000 ft Correct answer.

Explanation

The alveolar oxygen partial pressure stays close to sea-level values up to roughly 10,000 ft because the oxygen dissociation curve is still on its flat portion. Above that altitude the curve steepens and saturation falls progressively, which is why 10,000 ft is used as the practical threshold for supplemental oxygen in unpressurised flight.

Question 42Basic Aviation Physiology and Health Maintenance

A pilot breathing 100% oxygen at 34,000 ft in an unpressurised aircraft is protected against hypoxia because the oxygen provides an equivalent altitude of approximately:

  1. 24,000 ft
  2. 10,000 ft Correct answer.
  3. 34,000 ft
  4. 18,000 ft

Explanation

Breathing pure oxygen multiplies the inspired oxygen pressure by about five relative to air, giving an equivalent altitude roughly 24,000 ft below the actual cabin altitude. From 34,000 ft this yields an equivalent of about 10,000 ft, which is tolerable. This is the basis of the 'oxygen altitude' concept used in unpressurised operations.

Question 43Basic Aviation Physiology and Health Maintenance

Which symptom is most characteristic of the earliest stage of hypoxia in a pilot at altitude?

  1. Severe chest pain radiating to the arm
  2. Impaired judgement and euphoria Correct answer.
  3. Complete loss of consciousness without warning
  4. Blue discolouration of the lips appearing first

Explanation

The first effects of hypoxia are on the higher mental functions, producing euphoria, impaired judgement and reduced self-criticism before the pilot notices anything is wrong. Cyanosis and loss of consciousness occur later. Because judgement is affected first, the pilot is the least reliable person to detect their own hypoxia.

Question 44Basic Aviation Physiology and Health Maintenance

An aircraft cabin depressurises and the pilot's time of useful consciousness is quoted as about 30 seconds. Which altitude does this most closely correspond to?

  1. 25,000 ft
  2. 18,000 ft
  3. 35,000 ft Correct answer.
  4. 45,000 ft

Explanation

Time of useful consciousness falls steeply with altitude: roughly minutes at 25,000 ft but only around 30 to 60 seconds at 35,000 ft. At 45,000 ft useful consciousness is only about 10 to 15 seconds. Recognising these figures drives the immediate use of oxygen after depressurisation.

Question 45Basic Aviation Physiology and Health Maintenance

Which type of hypoxia is caused by breathing normally oxygenated air but having insufficient functional haemoglobin, as in carbon monoxide poisoning?

  1. Hypaemic hypoxia Correct answer.
  2. Hypoxic hypoxia
  3. Histotoxic hypoxia
  4. Stagnant hypoxia

Explanation

Hypaemic hypoxia arises when the blood's oxygen-carrying capacity is reduced, for example by anaemia or carbon monoxide binding haemoglobin. The lungs and inspired air may be normal, but the amount of oxygen delivered to tissues is inadequate. This distinguishes it from hypoxic, stagnant and histotoxic forms.

Question 46Basic Aviation Physiology and Health Maintenance

A pilot flying at 8,000 ft cabin altitude notices no symptoms but is a smoker. Why is this pilot at greater risk of hypoxia than a non-smoker at the same altitude?

  1. Nicotine increases the affinity of tissues for nitrogen
  2. Smoking increases lung volume and therefore oxygen demand
  3. Carbon monoxide in smoke reduces the oxygen-carrying capacity of the blood Correct answer.
  4. Smoking raises the alveolar oxygen partial pressure

Explanation

Carbon monoxide from smoking binds haemoglobin far more readily than oxygen, lowering the effective oxygen-carrying capacity and shifting the dissociation curve. A smoker therefore behaves as if at a higher altitude than the cabin altitude. This is why smokers have a lower effective ceiling before hypoxia appears.

Question 47Basic Aviation Physiology and Health Maintenance

During a rapid decompression at high altitude, why is it important to breathe 100% oxygen before or immediately after donning the mask rather than delaying?

  1. Oxygen washes out nitrogen and slows the onset of hypoxia, buying time Correct answer.
  2. Oxygen increases the cabin pressure automatically
  3. Oxygen prevents decompression sickness by recompressing the blood
  4. Oxygen warms the inspired air to prevent bronchospasm

Explanation

Immediate 100% oxygen maintains oxygen saturation and, if breathed before decompression, reduces nitrogen in the tissues, slowing bubble formation. The primary aim is to prevent the rapid onset of hypoxia while descending. Delaying even briefly at high altitude can cost useful consciousness.

Question 48Basic Aviation Physiology and Health Maintenance

What is the primary physiological effect of positive g acceleration on the cardiovascular system?

  1. Blood is displaced towards the lower body, reducing cerebral perfusion Correct answer.
  2. Pulmonary blood flow is diverted away from the lungs
  3. Blood is pooled in the head, raising cerebral pressure
  4. Heart rate falls sharply and cardiac output increases

Explanation

Positive g displaces blood towards the legs and abdomen, reducing venous return and cerebral perfusion, which can lead to greyout and then G-LOC. The body's baroreceptor reflex raises heart rate and peripheral resistance to compensate, but this may be insufficient at high sustained g.

Question 49Basic Aviation Physiology and Health Maintenance

An aircrew member experiences a greyout during a high-g manoeuvre. What does this indicate?

  1. Detachment of the retina from the choroid
  2. Retinal hypoxia from reduced cerebral and ocular blood flow Correct answer.
  3. Increased intraocular pressure from the mask
  4. Excess oxygen delivery to the retina

Explanation

Greyout is caused by reduced blood flow and oxygen delivery to the retina as positive g lowers arterial pressure at head level. It is a warning sign that G-LOC may follow if the g load is not reduced or countermeasures applied. Vision returns as perfusion is restored.

Question 50Basic Aviation Physiology and Health Maintenance

Which countermeasure most directly raises a pilot's tolerance to sustained positive g during a high-performance sortie?

  1. Breathing 100% oxygen at high flow only
  2. The anti-g straining manoeuvre combined with a properly fitted g-suit Correct answer.
  3. Rapid shallow breathing to increase oxygen intake
  4. Leaning the torso forward towards the instrument panel

Explanation

The anti-g straining manoeuvre tenses skeletal muscle and raises intrathoracic pressure to maintain venous return and arterial pressure at head level, while the g-suit compresses the legs and abdomen. Together they substantially increase g tolerance. Breathing technique alone or posture changes are less effective.