Aircraft General Knowledge: 9 Recent ATPL Questions Explained

Aircraft General Knowledge questions become particularly challenging when several systems, components and operating principles appear in the same scenario. The correct answer often depends on recognising exactly which part of the system the examiner is testing.

In this walkthrough, we break down nine recent Aircraft General Knowledge (021) questions from the Airhead ATPL Question Bank, all reported across multiple EASA authorities within the last 60 days.

The questions cover fuel systems, piston and turbine engines, passenger oxygen, cabin pressurisation, high-pressure hydraulics, wheel safety devices and asymmetric flight. Each answer is supported by a clear, exam-focused explanation and a practical tip to help you recognise similar questions more quickly.

This article is the text-based version of our recent video session, created for students who prefer reading or want a quick reference for revision.

Prefer to watch instead? Follow the complete video walkthrough: 9 Latest ATPL AGK Exam Questions Solved, where ATPL pilot Michal explains every question step by step.

9 Latest ATPL AGK Questions Explained | Mixed Aircraft Systems

• AIR-238309: Fuel Systems — Centre Tank Booster Pump Failure on a Multi-Tank Aircraft

• AIR-237908: Piston Engines — Carburettor Icing Effects

• AIR-274268: Oxygen Systems — Passenger Transport Aircraft Requirements

• AIR-237895: Turbine Engines — Why Large Jet Engines Require Spool-Up Time

• AIR-237414: Cabin Pressurisation — Pressure Controller Failure in Cruise

• AIR-237593: Hydraulic Systems — Advantages of High-Pressure Systems

• AIR-274190: Gas Turbine Engines — Airflow After the Compressor

• AIR-238207: Wheel Safety Devices — Function of a Fusible Plug

• AIR-237925: Multi-Engine Piston Aircraft — Rudder Control After Engine Failure During a Go-Around

Explore key subtopics & core concepts of the Aircraft General Knowledge

Question 1: Centre Tank Booster Pump Failure

Question ID AIR-238309: Consider a turbine-engined aeroplane with two underwing engines, fitted with two wing tanks and one centre tank. If all centre tank booster pumps fail…

1. part or all of the fuel in the centre tank is considered unusable.

2. fuel starvation may occur, which could lead to engine flame-out.

3. thrust deterioration may occur at high altitude.

4. fuel imbalance shall occur during high thrust settings.

Correct Answer: part or all of the fuel in the centre tank is considered unusable.

Explanation

Transport aircraft commonly use electrically driven booster pumps to deliver fuel from the tanks to the engines. Wing tanks may normally provide a limited gravity feed if their pumps fail, but the centre tank on many aircraft cannot feed the engines effectively without pump pressure.

If all centre-tank booster pumps fail, some or all of the fuel in that tank may therefore become unusable for the rest of the flight. The exact quantity depends on the aircraft's design, making this question partly type-specific. Even where limited gravity transfer is possible, the entire tank contents may not be available because fuel pick-up points are positioned above the lowest part of the tank to prevent water and sediment from entering the system.

The failure may also introduce operational restrictions, such as a lower maximum altitude, because gravity feed provides less reliable fuel pressure than normal pump operation. 

Exam Tip

Wing tanks may provide limited gravity feed. Centre tanks commonly depend on booster pumps. If all centre-tank pumps fail, expect part or all of the centre-tank fuel to become unusable.

Fuel Up! A Practical Guide to Aviation Fuel. Go deeper into aviation fuel types, tank systems, fuel management and the operational principles behind safe fuel supply.

Question 2: Why Carburettor Ice Can Form Above 0°C

Question ID AIR-237908: With respect to a piston engine aircraft, ice in the carburettor:

1. may form at OAT's higher than +10°C.

2. will only form at outside air temperatures OAT`s below the freezing point of water.

3. will only form at OAT`s below the freezing point of fuel.

4. will only form at OAT`s below +10°C.

Correct Answer: May form at OAT's higher than +10°C.

Explanation

A carburettor mixes air with finely atomised fuel before the mixture enters the engine cylinders. As the air passes through the carburettor venturi, its velocity increases and its static pressure falls. This pressure reduction causes a significant drop in temperature.

Fuel vaporisation cools the mixture even further. If enough moisture is present, ice can form around the venturi and throttle butterfly, gradually restricting airflow into the engine.

This is why carburettor icing can occur at outside-air temperatures well above 0°C. The relevant temperature is not simply the ambient temperature, but the much lower temperature reached inside the carburettor after the combined effects of pressure reduction and fuel vaporisation.

As the ice builds up, engine power decreases. In a fixed-pitch propeller aircraft, this is normally indicated by a reduction in RPM. In a constant-speed propeller aircraft, the first sign may instead be a drop in manifold pressure.

Exam Tip

Do not associate carburettor icing only with freezing weather. Remember the two cooling effects:

Venturi pressure drop + fuel vaporisation = possible icing well above 0°C.

Question 3: Passenger Aircraft Oxygen Requirements

Question ID AIR-274268: Which of these statements concerning oxygen on board passenger transport aeroplanes is correct?

1. Portable oxygen bottles in the cabin are primarily intended for first aid purposes.

2. After being activated, a chemical oxygen generator does not produce any heat.

3. A chemical oxygen generator can provide oxygen for at least one hour.

4. Since lavatories are not fitted with an oxygen system, they should be evacuated quickly in case of decompression.

Correct Answer: Portable oxygen bottles in the cabin are primarily intended for first aid purposes.

Explanation

Passenger transport aircraft require several forms of supplementary oxygen for different purposes.

Passenger drop-down masks may be supplied by chemical oxygen generators. Once activated, the chemical reaction produces oxygen for a limited period (typically around 15 minutes) and cannot be stopped. The reaction also generates considerable heat, so the statement that chemical generators remain cool is incorrect.

Oxygen provision is also required in areas such as lavatories, where a passenger could be during a decompression. Cabin crew must have access to portable oxygen equipment that allows them to move through the cabin and assist passengers.

Portable oxygen bottles carried in the passenger cabin are primarily intended for first aid and therapeutic use, rather than as the main emergency supply for every passenger. This makes that statement the correct answer.

Exam Tip

Match the oxygen source to its purpose:

• Drop-down masks: emergency decompression supply

• Portable bottles: first aid and cabin-crew mobility

• Chemical generators: limited duration, hot when operating, and impossible to stop once activated

Question 4: Why Large Jet Engines Require Spool-Up Time

Question ID AIR-237895: Why do large jet engines need a spool-up time?

1. A request for rapid acceleration may cause a flameout due to the overly rich mixture.

2. Because the engines are controlled by an electronic engine control unit, the calculations required to meter the correct amount of fuel produce a delay in the acceleration of the engine.

3. The engine gearbox requires a significant amount of the energy produced by the turbine; this causes a typical spool-up time.

4. Due to the number of turbine blades in jet fans and the high viscosity of cold lubricants.

Correct Answer: A request for rapid acceleration may cause a flameout due to the overly rich mixture.

Explanation

Large turbine engines cannot produce maximum thrust instantly because their compressors, turbines and fan assemblies have considerable rotational inertia. They need time to accelerate from a low rotational speed to the RPM required for high thrust.

When the thrust lever is advanced, the FADEC or engine control system increases fuel flow in a carefully scheduled manner. Adding too much fuel before sufficient airflow has developed could disturb the pressure balance through the compressor, increase turbine temperature excessively, or contribute to compressor stall, surge or flameout.

The engine control system therefore matches fuel flow to the available airflow and current spool speed. As the compressor and fan accelerate, progressively more fuel can be introduced safely until the commanded thrust is reached.

This delay is particularly noticeable when a large engine is operating near idle. It is also why pilots must anticipate the need for thrust during phases such as approach and go-around rather than expecting an immediate response.

Exam Tip

The delay is not simply caused by a computer taking time to calculate. Think:

Large rotating mass + controlled fuel scheduling = safe spool-up.

Rapid, uncontrolled fuel addition could destabilise the engine rather than accelerate it safely.

Question 5: Pressure Controller Failure in Cruise

Question ID AIR-237414: During level cruising flight, an aeroplane experiences a malfunction of the pressure controller. If the cabin vertical speed indicator reads 200 ft/min rate of descent…

1. the differential pressure will rise to its maximum value, thus causing the safety relief valves to open.

2. a descent must be initiated to prevent the oxygen masks dropping when the cabin altitude reaches 14000 ft.

3. the aircraft has to climb to a higher flight level in order to reduce the cabin altitude to its initial value.

4. the crew has to intermittently cut off the incoming air flow in order to maintain a zero cabin altitude.

Correct Answer: The differential pressure will rise to its maximum value, thus causing the safety relief valves to open.

Explanation

A cabin vertical speed indication of 200 ft/min descent means that the cabin altitude is decreasing. In other words, the pressure inside the cabin is increasing.

Because the aircraft remains in level cruise, the outside pressure is broadly unchanged. The increasing cabin pressure therefore raises the pressure difference between the inside and outside of the fuselage, known as differential pressure (ΔP).

The aircraft structure is designed to tolerate differential pressure only up to a specified maximum. If the pressure controller fails and ΔP continues to rise, the positive pressure-relief valves open automatically. They release enough cabin air to prevent the differential pressure from exceeding the structural limit.

The relief valves do not remove pressurisation completely. They regulate the excess pressure and hold ΔP close to the maximum permitted value.

Exam Tip

Read the cabin indication carefully:

• Cabin descending: cabin pressure is increasing.

• Cabin climbing: cabin pressure is decreasing.

In level flight, a descending cabin means ΔP rises until the relief valves limit it.

Question 6: High-Pressure Hydraulic System Advantages

Question ID  AIR-237593: Which one of the following is an advantage of a high-pressure hydraulic system over a low-pressure hydraulic system?

1. A high-pressure system is able to handle greater loads than a low-pressure system.

2. A high-pressure system is safer than a low-pressure system with regard to hydraulic fluid leaks.

3. A high-pressure system is more reliable than a low-pressure system.

4. A high-pressure system is simpler and lighter than a low-pressure system.

Correct Answer: A high-pressure system is able to handle greater loads than a low-pressure system.

Explanation

Hydraulic force depends on the pressure applied to a given actuator area. Increasing system pressure allows the actuator to produce a greater force or, alternatively, allows a smaller and lighter actuator to produce the same force.

Most transport aircraft hydraulic systems operate at approximately 3,000 psi. Some aircraft use pressures closer to 5,000 psi, allowing the system to move heavy flight controls, landing gear and other large loads while reducing the size and weight of certain components.

The main advantage is therefore the ability to handle greater loads and achieve a high power-to-weight ratio.

However, higher pressure is not an advantage without trade-offs. Components, seals, pipes and connections experience greater stress, and the system requires more sophisticated design, inspection and maintenance. This is why many manufacturers retain the established 3,000 psi standard.

Exam Tip

For the principal advantage, choose:

Greater force and load capability.

Possible weight savings are a related benefit, while higher cost, stress and maintenance requirements are disadvantages.

Aircraft General Knowledge: 5 Recent ATPL Questions Solved. Continue your AGK revision with five recent Hydraulics questions covering system pressure, hydraulic fuses, cargo-door operation and high-pressure systems.

Question 7: Airflow Through a Gas Turbine Compressor

Question ID AIR-274190: After air has passed through the compressor of a gas turbine engine the:

1. temperature will be higher than the inlet temperature.

2. velocity will be higher than the inlet velocity.

3. pressure will be the same as the inlet pressure.

4. velocity will be the same as the inlet velocity.

Correct Answer: The temperature will be higher than the inlet temperature.

Explanation

The compressor raises the pressure of the air before it enters the combustion chamber. As the air is compressed into a smaller effective volume, its pressure, density and temperature all increase.

The temperature rise is not caused by combustion at this stage. It is a direct result of the work done on the air during compression.

The compressor must provide the combustion chamber with a stable supply of high-pressure air. Fuel is then introduced and burned, causing a much larger temperature increase. The hot gases expand through the turbine and exhaust sections, where their energy is converted into turbine work and propulsive thrust.

The examiner is testing the compressor stage specifically, so do not jump ahead to what happens during combustion or exhaust expansion.

Exam Tip

Across the compressor: Pressure ↑ | Temperature ↑ | Density ↑

Fuel has not yet been burned, but compression alone already raises the air temperature.

Question 8: How Fusible Plugs Protect Aircraft Tyres

Question ID AIR-238207: The function of a fusible plug is to:

1. protect the brake against brake disk fusion due to excessive temperature.

2. act as a special circuit breaker in the electrical system.

3. protect against excessive pressure in the pneumatic system.

4. protect the tyre against explosion due to excessive temperature.

Correct Answer: Protect the brake against brake disk fusion due to excessive temperature.

Explanation

Heavy braking (particularly during a rejected take-off) can transfer enormous heat into the wheel and tyre assembly. If the tyre pressure rises unchecked as the wheel heats up, the tyre may burst violently and endanger the aircraft and anyone nearby.

A fusible plug prevents this by containing a material designed to melt at a predetermined temperature. This temperature is reached before the wheel or tyre assembly becomes dangerously overstressed.

Once the plug melts, the tyre deflates in a controlled manner. The tyre may no longer be serviceable, but the gradual pressure release is far safer than an explosive burst.

The plug therefore protects the wheel assembly against the consequences of excessive heat, rather than responding directly to excessive pressure alone.

Exam Tip

Think: Hot brakes → fusible plug melts → controlled tyre deflation. Its purpose is to prevent a heat-induced tyre explosion.

Question 9: Critical Engine Failure and Crosswind

Question ID AIR-237925: A multi-engine piston aircraft: both the propellers rotate clockwise as seen from the cockpit. In a go-around, one of the engines fails. Which of the following situations will most probably need the pilot to use full rudder deflection?

1. Left engine failure, left crosswind.

2. Left engine failure, right crosswind.

3. Right engine failure, left crosswind.

4. Right engine failure, right crosswind.

Correct Answer: Left engine failure, left crosswind.

Explanation

With both propellers rotating clockwise as viewed from the cockpit, the descending blade is on the right side of each propeller disc. Because the descending blade produces more thrust at a high angle of attack, the effective thrust line of each engine moves slightly to the right.

The right engine’s thrust therefore acts farther from the aircraft centreline than the left engine’s thrust. If the left engine fails, the remaining right engine produces the greatest possible yawing moment. The left engine is consequently the critical engine.

The situation becomes even more demanding during a go-around because the aircraft is at low speed, high power and often in a high-drag configuration. Rudder effectiveness is relatively limited while asymmetric thrust is at or near its greatest.

A left crosswind makes conditions more adverse. The aircraft tends to weathercock into the wind, producing an additional yaw to the left—the same direction as the yaw caused by failure of the left engine. The pilot may therefore need full opposite rudder to maintain directional control.

Exam Tip

For clockwise-turning propellers:

• Left engine = critical engine

• Left engine failure + left crosswind = most adverse combination

Remember that the worst case combines maximum asymmetric thrust with a crosswind that reinforces the same yawing direction.

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