01.043.021 – PRESSURISATION, OXYGEN AND EMERGENCY EQUIPMENT

01.043.021.001 — Explain why oxygen availability falls with altitude even though the oxygen percentage of air remains roughly constant.

A. Oxygen availability falls with altitude because the total atmospheric pressure increases, which reduces the partial pressure of oxygen, even though oxygen still represents about 21% of the air by volume.

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B. Passenger oxygen systems generally provide continuous-flow oxygen through drop-down masks after automatic or commanded deployment. Crew oxygen systems use diluter-demand regulators, so oxygen is delivered only during inhalation and may be mixed with cabin air or supplied as 100% oxygen depending on the selected mode and altitude.

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C. Oxygen availability falls with altitude because the total atmospheric pressure decreases, which reduces the partial pressure of oxygen, even though oxygen still represents about 21% of the air by volume.

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D. Above 12,500 ft up to and including 14,000 ft, the required minimum flight crew must use supplemental oxygen for any portion of the flight exceeding 30 minutes at those altitudes. Above 14,000 ft, the required minimum flight crew must use supplemental oxygen continuously. Above 15,000 ft, each occupant must be provided with supplemental oxygen.

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01.043.021.002 — State the role of the outflow valve in cabin pressurisation control.

A. The outflow valve is the primary modulating device that controls cabin pressure by metering the amount of air discharged overboard.

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B. The inflow valve is the primary modulating device that controls cabin pressure by metering the amount of air discharged overboard.

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C. Dual-stage engine bleed systems normally use an intermediate compressor stage when it provides sufficient pressure. At low engine RPM, the system changes to a higher compressor stage to restore the required pressure margin. The interstage check valve prevents reverse flow from the higher-pressure stage into the lower-pressure stage ducting.

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D. The positive pressure relief valve opens automatically if cabin differential pressure becomes too high, protecting the fuselage from overpressure. The negative pressure relief valve opens when ambient pressure exceeds cabin pressure by a threshold, protecting the structure from excessive inward loading. The dump valve is used to rapidly depressurise the cabin when commanded or when required by system logic.

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01.043.021.003 — Distinguish the functions of the positive pressure relief valve, negative pressure relief valve, and dump valve.

A. The positive pressure relief valve opens automatically if cabin differential pressure becomes too low, protecting the fuselage from overpressure. The negative pressure relief valve opens when ambient pressure exceeds cabin pressure by a threshold, protecting the structure from excessive inward loading. The dump valve is used to rapidly depressurise the cabin when commanded or when required by system logic.

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B. The outflow valve is the primary modulating device that controls cabin pressure by metering the amount of air discharged overboard.

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C. The positive pressure relief valve opens automatically if cabin differential pressure becomes too high, protecting the fuselage from overpressure. The negative pressure relief valve opens when ambient pressure exceeds cabin pressure by a threshold, protecting the structure from excessive inward loading. The dump valve is used to rapidly depressurise the cabin when commanded or when required by system logic.

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D. Dual-stage engine bleed systems normally use an intermediate compressor stage when it provides sufficient pressure. At low engine RPM, the system changes to a higher compressor stage to restore the required pressure margin. The interstage check valve prevents reverse flow from the higher-pressure stage into the lower-pressure stage ducting.

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01.043.021.004 — Compare passenger continuous-flow oxygen with crew diluter-demand oxygen.

A. Passenger oxygen systems generally provide continuous-flow oxygen through drop-down masks before automatic or commanded deployment. Crew oxygen systems use diluter-demand regulators, so oxygen is delivered only during inhalation and may be mixed with cabin air or supplied as 100% oxygen depending on the selected mode and altitude.

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B. Oxygen availability falls with altitude because the total atmospheric pressure decreases, which reduces the partial pressure of oxygen, even though oxygen still represents about 21% of the air by volume.

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C. Above 12,500 ft up to and including 14,000 ft, the required minimum flight crew must use supplemental oxygen for any portion of the flight exceeding 30 minutes at those altitudes. Above 14,000 ft, the required minimum flight crew must use supplemental oxygen continuously. Above 15,000 ft, each occupant must be provided with supplemental oxygen.

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D. Passenger oxygen systems generally provide continuous-flow oxygen through drop-down masks after automatic or commanded deployment. Crew oxygen systems use diluter-demand regulators, so oxygen is delivered only during inhalation and may be mixed with cabin air or supplied as 100% oxygen depending on the selected mode and altitude.

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01.043.021.005 — State the FAA supplemental oxygen requirements for unpressurised operations above 12,500 ft, 14,000 ft, and 15,000 ft cabin altitude.

A. Above 12,500 ft up to and including 14,000 ft, the required maximum flight crew must use supplemental oxygen for any portion of the flight exceeding 30 minutes at those altitudes. Above 14,000 ft, the required minimum flight crew must use supplemental oxygen continuously. Above 15,000 ft, each occupant must be provided with supplemental oxygen.

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B. The outflow valve is the primary modulating device that controls cabin pressure by metering the amount of air discharged overboard.

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C. Above 12,500 ft up to and including 14,000 ft, the required minimum flight crew must use supplemental oxygen for any portion of the flight exceeding 30 minutes at those altitudes. Above 14,000 ft, the required minimum flight crew must use supplemental oxygen continuously. Above 15,000 ft, each occupant must be provided with supplemental oxygen.

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D. Oxygen availability falls with altitude because the total atmospheric pressure decreases, which reduces the partial pressure of oxygen, even though oxygen still represents about 21% of the air by volume.

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01.043.021.006 — Explain why the outflow valve is not simply “closed at high altitude.”

A. The outflow valve continuously modulates to satisfy cabin altitude schedule, cabin rate limits, and minimum differential-pressure limits.

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B. A pressure reducer actively maintains a lower downstream working pressure during normal operation, while a pressure relief valve opens only when pressure exceeds a safety limit.

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C. The outflow valve continuously modulates to satisfy cabin altitude schedule, cabin rate limits, and maximum differential-pressure limits.

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D. In gradual decompression, pressure loss develops slowly enough that obvious physical signs may be absent initially.

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01.043.021.007 — Explain the purpose of pre-pressurisation before take-off.

A. Pre-pressurisation creates a small positive cabin pressure relative to ambient after lift-off.

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B. The pre-cooler reduces engine bleed air temperature before the air is distributed to downstream pneumatic users. Fan air flow through the pre-cooler is regulated by a fan air valve, which modulates cooling airflow according to bleed outlet temperature.

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C. The outflow valve continuously modulates to satisfy cabin altitude schedule, cabin rate limits, and maximum differential-pressure limits.

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D. Pre-pressurisation creates a small positive cabin pressure relative to ambient before lift-off.

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01.043.021.008 — Explain why gradual decompression can be operationally more insidious than rapid decompression.

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. The outflow valve continuously modulates to satisfy cabin altitude schedule, cabin rate limits, and maximum differential-pressure limits.

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C. In gradual decompression, pressure loss develops slowly enough that obvious physical signs may be absent initially.

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D. Passenger masks are designed primarily for hypoxia protection, not for shielding the eyes and face from smoke or fumes.

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01.043.021.009 — Explain why passenger drop-down oxygen masks are not suitable as smoke-protective equipment.

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. Passenger masks are designed primarily for hypoxia protection, not for shielding the eyes and face from smoke or fumes.

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C. First-aid oxygen equipment must provide at least 4 litres per minute per user, although a means may exist to reduce this to not less than 2 litres per minute at any cabin altitude.

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D. The outflow valve continuously modulates to satisfy cabin altitude schedule, cabin rate limits, and maximum differential-pressure limits.

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01.043.021.010 — Explain why passenger oxygen is usually continuous-flow while crew oxygen is demand-regulated.

A. Passenger systems favour simplicity, rapid deployment, and reliable operation across many seats at once, whereas crew systems are designed for efficiency, longer endurance, and better physiological control.

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B. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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C. Oxygen availability falls with altitude because the total atmospheric pressure decreases, which reduces the partial pressure of oxygen, even though oxygen still represents about 21% of the air by volume.

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D. The outflow valve continuously modulates to satisfy cabin altitude schedule, cabin rate limits, and maximum differential-pressure limits.

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01.043.021.011 — State the basic oxygen flow requirement for first-aid oxygen equipment when installed.

A. First-aid oxygen equipment must provide at least 4 litres per minute per user, although a means may exist to increase this to not less than 2 litres per minute at any cabin altitude.

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B. Passenger masks are designed primarily for hypoxia protection, not for shielding the eyes and face from smoke or fumes.

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C. CS-25 requires protective breathing equipment to supply oxygen for 15 minutes per crew member at a pressure altitude of 8,000 ft.

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D. First-aid oxygen equipment must provide at least 4 litres per minute per user, although a means may exist to reduce this to not less than 2 litres per minute at any cabin altitude.

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01.043.021.012 — Explain why a lower commanded cabin rate of climb may cause the pressurisation system to reach maximum differential pressure earlier in the climb.

A. Holding the cabin at a lower effective altitude for longer decreases the pressure difference between cabin and ambient as the aircraft climbs.

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B. Holding the cabin at a lower effective altitude for longer increases the pressure difference between cabin and ambient as the aircraft climbs.

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C. Pressure rise usually indicates that the first actuator has reached the end of its travel or that the required upstream condition has been achieved.

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D. A pressure reducer maintains a lower controlled downstream pressure during normal operation. A pressure relief valve remains closed in normal operation and opens only when pressure exceeds a safe limit.

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01.043.021.013 — State the structural purpose of blow-out panels between cabin and cargo compartments.

A. The system is intended mainly for indication and monitoring; it does not directly affect the relevant control, protection, or power function.

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B. Blow-out panels allow rapid pressure equalisation between compartments during decompression.

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C. A pressure-maintaining valve protects essential services by restricting or cutting off supply to non-essential consumers when system pressure falls below a threshold.

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D. A hydraulic fuse automatically closes or restricts flow when abnormally high downstream flow indicates a line rupture or major leak.

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01.043.021.014 — Explain why time of useful consciousness decreases so sharply with altitude.

A. As altitude decreases, oxygen partial pressure falls further and the body reaches incapacitating hypoxia much more quickly.

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B. Pressure rise usually indicates that the first actuator has reached the end of its travel or that the required upstream condition has been achieved.

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C. If fan air cannot pass through the pre-cooler, bleed-air outlet temperature may exceed system limits.

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D. As altitude increases, oxygen partial pressure falls further and the body reaches incapacitating hypoxia much more quickly.

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01.043.021.015 — Explain why the outflow valve is the primary control element in pressurisation but not the structural protection device.

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. Windshield heating prevents ice accretion and preserves external visibility, but it also protects the windshield from cold-soak brittleness and reduces the risk of cracking.

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C. The inner pane is non-structural and pressure-equalised, while the pressure pane is designed to carry nearly all cabin pressurisation load.

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D. Its role is to modulate discharge airflow to maintain cabin schedule and differential pressure in normal operation.

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01.043.021.016 — Explain why rapid decompression is usually less violent than explosive decompression, yet still operationally critical.

A. Pressure equalisation occurs over seconds rather than almost instantaneously, so the transient is more extreme.

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B. Air extracted from a higher compressor stage is generally hotter.

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C. Pressure equalisation occurs over seconds rather than almost instantaneously, so the transient is less extreme.

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D. Air removed from the compressor is no longer fully available to the main propulsion cycle.

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01.043.021.017 — Discuss the role of the positive pressure relief valve in cabin pressurisation.

A. The negative pressure relief valve protects the fuselage by opening automatically if cabin differential pressure exceeds the structural limit.

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B. A non-return valve prevents reverse flow and preserves the intended source priority between branches or systems.

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C. The positive pressure relief valve protects the fuselage by opening automatically if cabin differential pressure exceeds the structural limit.

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D. Locked-wheel protection fully releases brake pressure on a wheel that decelerates to zero or near-zero speed.

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01.043.021.018 — Discuss the role of the negative pressure relief valve.

A. The negative pressure relief valve protects the aircraft structure when ambient pressure becomes significantly higher than cabin pressure.

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B. The negative pressure relief valve protects the aircraft structure when ambient pressure becomes significantly lower than cabin pressure.

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C. A non-return valve prevents reverse flow and preserves the intended source priority between branches or systems.

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D. Locked-wheel protection fully releases brake pressure on a wheel that decelerates to zero or near-zero speed.

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01.043.021.019 — Analyse the safety purpose of blow-out panels between cabin and cargo compartments.

A. No significant operational change would be expected because the affected function is automatically compensated for without any change in system capability.

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B. If anti-skid becomes inoperative, the system disconnects and the brakes revert to full manual operation.

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C. Blow-out panels allow rapid pressure equalisation between compartments during decompression.

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D. Emergency or standby braking capability is reduced because the accumulator stores less usable hydraulic energy.

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01.043.021.020 — Assess why gradual decompression can be harder for a crew to detect than explosive decompression.

A. No significant operational change would be expected because the affected function is automatically compensated for without any change in system capability.

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B. Gradual decompression may develop with few immediate physical cues.

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C. Cabin fog indicates rapid cooling and condensation caused by the sudden pressure drop.

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D. Pre-pressurisation smooths the lift-off transition and helps maintain a slight outward pressure gradient while still on the ground.

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01.043.021.021 — Interpret a sudden cabin fog immediately after decompression.

A. No significant operational change would be expected because the affected function is automatically compensated for without any change in system capability.

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B. Gradual decompression may develop with few immediate physical cues.

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C. If booster-pump pressure is lost, the jet ejector pump becomes ineffective.

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D. Cabin fog indicates rapid cooling and condensation caused by the sudden pressure drop.

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01.043.021.022 — Assess the operational value of pre-pressurisation before take-off.

A. No significant operational change would be expected because the affected function is automatically compensated for without any change in system capability.

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B. Pre-pressurisation smooths the lift-off transition and helps maintain a slight outward pressure gradient while still on the ground.

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C. FCII is primarily used to reduce the likelihood of ice formation from water present in the fuel system.

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D. Water contamination can lead to filter icing, fuel-flow restriction, and possible engine flameout.

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01.043.021.023 — Analyse why a lower scheduled cabin rate of climb is not always better.

A. A lower cabin climb rate improves comfort, but it can cause the system to reach minimum differential pressure earlier in the climb.

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B. A lower cabin climb rate improves comfort, but it can cause the system to reach maximum differential pressure earlier in the climb.

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C. Cabin fog indicates rapid cooling and condensation caused by the sudden pressure drop.

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D. Comparing these figures helps the crew validate fuel-system behaviour in real time.

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01.043.021.024 — State the crew protective-breathing-equipment duration commonly required by CS-25 and the purpose of that requirement.

A. CS-25 requires protective breathing equipment to supply oxygen for 5 minutes per crew member at a pressure altitude of 8,000 ft.

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B. First-aid oxygen equipment must provide at least 4 litres per minute per user, although a means may exist to reduce this to not less than 2 litres per minute at any cabin altitude.

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C. It allows the crew to compare independent perspectives on the same fuel state: quantity remaining, quantity consumed, and quantity expected.

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D. CS-25 requires protective breathing equipment to supply oxygen for 15 minutes per crew member at a pressure altitude of 8,000 ft.

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01.043.021.025 — Explain why passenger drop-down oxygen masks are described as hypoxia protection rather than smoke protection.

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. A dump valve is used to command rapid cabin depressurisation, whereas a positive pressure relief valve opens automatically to protect the fuselage from excessive differential pressure.

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C. They provide emergency oxygen, but they do not seal the eyes and face from the surrounding contaminated atmosphere.

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D. AVTAG is more volatile and has a lower flash point than kerosene-based jet fuel, and its lower density also affects fuel metering.

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01.043.021.026 — Explain why a dump valve and a positive pressure relief valve must not be confused.

A. A dump valve is used to command rapid cabin depressurisation, whereas a negative pressure relief valve opens automatically to protect the fuselage from excessive differential pressure.

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B. A dump valve is used to command rapid cabin depressurisation, whereas a positive pressure relief valve opens automatically to protect the fuselage from excessive differential pressure.

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C. A restrictor valve gives free flow in one direction and metered flow in the other, whereas a flow-control valve regulates flow to maintain a more constant actuator speed.

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D. A shuttle valve automatically selects the higher of two pressure sources to feed one service, whereas a non-return valve only permits one-way flow and blocks reverse flow.

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01.043.021.027 — Explain why passenger oxygen deployment altitude matters operationally.

A. It is set to provide oxygen after cabin altitude rises to a level where passengers may become incapacitated.

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B. It is set to provide oxygen before cabin altitude rises to a level where passengers may become incapacitated.

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C. Fuel-flow data allows fuel-used calculation, supports fuel prediction, and helps detect abnormal consumption trends.

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D. Oxygen is supplied only during inhalation, and cabin air may be mixed in automatically when appropriate.

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01.043.021.028 — Explain why a diluter-demand crew oxygen system is more economical than continuous flow.

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. Protective breathing equipment must supply protective oxygen for 15 minutes per crew member at a pressure altitude of 8,000 ft.

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C. Oxygen is supplied only during inhalation, and cabin air may be mixed in automatically when appropriate.

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D. It is set to provide oxygen before cabin altitude rises to a level where passengers may become incapacitated.

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01.043.021.029 — State the CS-25 requirement for protective breathing equipment oxygen duration for crew members.

A. Protective breathing equipment must supply protective oxygen for 5 minutes per crew member at a pressure altitude of 8,000 ft.

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B. Oxygen is supplied only during inhalation, and cabin air may be mixed in automatically when appropriate.

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C. Structural icing in flight requires visible moisture and a temperature at the point of impact that is at or below freezing.

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D. Protective breathing equipment must supply protective oxygen for 15 minutes per crew member at a pressure altitude of 8,000 ft.

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01.043.021.030 — Explain why the outflow valve is central to pressure control but cannot by itself guarantee structural safety.

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. Crossfeed preserves the ability to supply an engine from an alternate source after a failure, whereas transfer is mainly used for balancing, CG control, or tank-management logic.

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C. High-stage bleed is hotter and imposes a greater engine-performance and thermal-management penalty.

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D. It is the primary normal regulating device, but it remains a control element subject to failure or miscommand.

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01.043.021.031 — Explain why passenger oxygen systems are designed around fast automatic deployment rather than fine physiological regulation.

A. Their main purpose is to provide rapid hypoxia protection to many occupants simultaneously after a depressurisation event.

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B. Their main purpose is to provide rapid hypoxia protection to many occupants simultaneously before a depressurisation event.

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C. It also smooths pressure fluctuations, damps transients, and supplies peak short-duration flow demand during normal operation.

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D. Ambient pressure is lower at altitude, so pump inlet conditions are more vulnerable to cavitation.

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01.043.021.032 — What would you expect if the outflow valve failed fully closed while pack inflow continued?

A. Cabin differential pressure would rise rapidly.

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B. No significant operational change would be expected because the affected function is automatically compensated for without any change in system capability.

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C. Fuel-feed margin to the engine-driven pump could become insufficient.

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D. Valve performance could become erratic or degraded.

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01.043.021.033 — What would be the consequence of a gradual decompression going unrecognised?

A. Crew performance could degrade before obvious physical symptoms are noticed.

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B. Crew performance could degrade after obvious physical symptoms are noticed.

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C. Bleed-air temperature downstream could rise beyond safe limits.

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D. Pressure smoothing and stored-energy capability would both be reduced.

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01.043.021.034 — Why is the outflow valve the core of normal pressurisation control?

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. The pressure-relief protection system.

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C. Because cabin pressure is regulated by controlling how much air leaves the fuselage.

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D. Because each indication describes a different aspect of the same fuel state.

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01.043.021.035 — Why are relief valves still required even when automatic pressurisation control is working normally?

A. Because the design removes the need for the associated protection or control function and therefore has no meaningful effect on loads, flow, pressure, or controllability.

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B. Because each indication describes a different aspect of the same fuel state.

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C. Because it allows one fuel source to continue feeding an engine if the normal supply path is no longer available.

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D. Because structural protection must remain available if the normal control element fails.

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01.043.021.036 — Why is passenger oxygen designed around immediate availability rather than oxygen economy?

A. Because the system must provide simple, rapid emergency protection to many occupants at once before a decompression.

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B. Because the system must provide simple, rapid emergency protection to many occupants at once after a decompression.

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C. Because each indication describes a different aspect of the same fuel state.

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D. Because it allows one fuel source to continue feeding an engine if the normal supply path is no longer available.

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01.043.021.037 — The outflow valve fails closed in flight while pack inflow continues. What protects the fuselage next?

A. No significant operational change would be expected because the affected function is automatically compensated for without any change in system capability.

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B. Because lower altitude increases ambient pressure and improves fuel-feed margin to the engine-driven pump.

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C. The correct concern is that there may be a leak, an indication problem, or abnormal fuel consumption.

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D. The pressure-relief protection system.

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01.043.021.038 — A decompression is slow and initially subtle. Why can that be more dangerous than it sounds?

A. Because crew awareness may lag ahead the physiological effects of hypoxia.

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B. Because crew awareness may lag behind the physiological effects of hypoxia.

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C. The correct concern is that there may be a leak, an indication problem, or abnormal fuel consumption.

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D. Because low temperature can increase viscosity and promote wax formation, which may restrict fuel flow.

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01.043.021.039 — Passenger oxygen masks deploy. Why is that not the same as giving passengers smoke protection?

A. No significant operational change would be expected because the affected function is automatically compensated for without any change in system capability.

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B. Because those masks are designed for emergency oxygen supply, not for isolating the user from a smoky atmosphere.

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C. The correct concern is that there may be a leak, an indication problem, or abnormal fuel consumption.

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D. Because low temperature can increase viscosity and promote wax formation, which may restrict fuel flow.

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01.043.021 – PRESSURISATION, OXYGEN AND EMERGENCY EQUIPMENT

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