Aircraft General Knowledge: 5 Recent ATPL Questions Solved
Let’s practise together five of the latest Aircraft General Knowledge (021) questions from the Airhead ATPL Question Bank, all reported across multiple EASA authorities. This walkthrough is designed for ATPL students looking to sharpen their AGK theory with real, exam-relevant material.
The session focuses on 02103 – Hydraulics, covering system pressure, flow demand, key component functions, and common ATPL exam traps, with clear, exam-oriented explanations for each question.
Hydraulics are among the most powerful systems on any aircraft. They operate the landing gear, brakes, flaps, and even primary flight controls. The reason is simple: hydraulics are powerful, reliable, and compact. A relatively small quantity of fluid under high pressure can generate enormous force — delivering the strength and precision that aviation demands.
Watch the full walkthrough:The content below is a text-based version of a recent video session, created for those who prefer reading to watching.
Questions Covered
AIR-238133: Purpose and Operation of a Hydraulic Fuse
AIR-238370: Primary Uses of Aircraft Hydraulic Systems
AIR-238568: Causes and Indications of Hydraulic Low-Pressure Warnings
AIR-238206: Backup Hydraulic Pressure Sources for Cargo Door Operation
AIR-237593: Advantages of High-Pressure vs Low-Pressure Hydraulic Systems
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Question 1: Function of a Hydraulic Fuse
Question ID AIR-238133: The function of a hydraulic fuse is to:
prevent total system loss in the event of hydraulic leak.
switch to the secondary system in the event of a leak in the primary brake system.
allow by-passing of the hydraulic pump in the event of excessive pressure.
protect against contamination
Correct Answer: prevent total system loss in the event of hydraulic leak.
Explanation: Hydraulic fuses are installed at various points throughout the aircraft hydraulic system. Their main purpose is system protection.
If a component downstream fails (such as a ruptured line, detached landing gear, or damaged actuator) the hydraulic fuse automatically closes when it senses an abnormal flow rate. This prevents:
Total depressurisation of the hydraulic system
Loss of the entire hydraulic fluid quantity
A good way to visualise this is a landing gear failure during take-off. If a gear or line is torn away, the hydraulic fuse upstream of that component closes, isolating the leak and protecting the rest of the system.
Hydraulic fuses may be installed before:
Landing gear systems
Flap actuators
Flight control actuators
Engine-related hydraulic consumers
Without hydraulic fuses, a single leak could drain the entire system and render it unusable.
Exam Tip: ATPL questions often distinguish between local protection and system-wide protection. If the question mentions preventing total system loss, a hydraulic fuse is a strong candidate.
Question 2: Main Use of Aircraft Hydraulic Systems
Question ID AIR-238370: Aircraft hydraulic systems are mainly used for...
absorbing shock during taxiing and touch down.
cooling and lubricating sliding and rotating components
controlling and actuating large and heavy surfaces.
damping powerplant and fuselage vibrations
Correct Answer: controlling and actuating large and heavy surfaces.
Explanation: Hydraulic systems operate using an incompressible fluid to transmit force. This makes them ideal for generating very high forces and overcoming strong aerodynamic loads.
In aircraft, hydraulics are primarily used to move large, heavy control surfaces, such as:
Primary flight controls
Flaps and slats
Landing gear
Spoilers and brakes
Even in modern fly-by-wire aircraft, hydraulics remain essential. While the control signals may be electrical, the actual movement of surfaces is usually hydraulically powered.
This applies to both Airbus and Boeing aircraft, where systems are often described as:
Electrically commanded
Hydraulically operated
Exam Tip: Be careful with wording. Hydraulics are not mainly for precision or speed—they are mainly for force generation.
Question 3: First Indication of Hydraulic Low Pressure
Question ID AIR-238568: A hydraulic low-pressure alert is the first indication of:
the pump output pressure being insufficient.
the hydraulic system accumulator becoming deflated.
the reservoir level being at minimum acceptable level.
a leak in the reservoir return line.
Correct Answer: the pump output pressure being insufficient.
Explanation: This question is a classic ATPL trap because several answers may seem logical at first glance. The key word is “first”.
Hydraulic system pressure indications are measured immediately downstream of the pump. Therefore, the first detectable abnormality is always related to the pump’s inability to maintain pressure.
Why not other options?
Reservoir leak: Initially masked by accumulators
Accumulator deflation: No immediate indication while pressure is maintained
System leak: The pump and accumulator compensate first
Only after these compensations are exhausted does the system pressure drop enough to trigger a warning.
Exam Tip: When you see first indication, think sensor location. In hydraulics, pressure sensors are placed after the pump.
Question 4: Hydraulic Power for Cargo Doors (Engines Off)
Question ID AIR-238206: Which of the following sources of hydraulic pressure is commonly used for operation of cargo doors when the electric hydraulic pumps are not working?
Hydraulic accumulator.
Hand pump.
Engine-driven pump.
Ram air turbine.
Correct Answer: Hand pump.
Explanation: Cargo doors are large, heavy and hydraulically operated. They are typically used when the engines are shut down, for safety and operational reasons.
Since engine-driven pumps are unavailable, alternative methods are required:
Electric hydraulic pump: Commonly used (e.g. Airbus Yellow system)
Manual hydraulic pump: Allows ground personnel to operate doors without engines or full electrical power
Why not the other options?
Engine-driven pump: Engines are off
Hydraulic accumulator: Limited energy, mainly for transient use (e.g. braking)
Ram Air Turbine (RAT): Emergency-only system, not for ground operations
Exam Tip: If the question involves ground operations with engines off, always consider manual or electric pumps before emergency systems.
Question 5: Advantage of High-Pressure Hydraulic Systems
Question ID AIR-237593: Which one of the following is an advantage of a high-pressure hydraulic system over a low-pressure hydraulic system?
A high-pressure system is able to handle greater loads than a low-pressure system.
A high-pressure system is safer than a low-pressure system with regard to hydraulic fluid leaks.
A high-pressure system is more reliable than a low-pressure system.
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: Most modern CAT aircraft operate hydraulic systems at approximately 3,000 psi, which is the standard benchmark.
Higher-pressure systems provide greater force output, ability to move larger surfaces and improved power-to-weight ratio. Some aircraft, such as the A380, operate at pressures up to 5,000 psi. An additional advantage of higher pressure is reduced system weight, due to smaller actuators and less hydraulic fluid.
However, there are trade-offs:
Increased system complexity
Higher structural stress
Greater maintenance and monitoring requirements
Exam Tip: If asked for the main advantage, always choose greater load capability. Weight savings are secondary and aircraft-specific.
Aircraft General Knowledge Exam Overview
To help you plan your revision, we’ve included a brief overview of the ATPL Aircraft General Knowledge (AGK) exam. This section gives you a clear snapshot of what to expect on exam day — including the exam format, timing, and overall difficulty — along with practical study guidance to help you prepare efficiently.
Exam Facts
Number of Questions: 80
Exam Duration: 2 hours
Difficulty Level: Medium
84% of papers passed
The official EASA subject title is Aircraft General Knowledge – Airframe, Systems and Power Plant, commonly abbreviated to Aircraft General Knowledge or simply AGK.
The syllabus covers the construction, components, and systems of an aircraft, focusing on their purpose and principles of operation. The volume of material is significant, but the concepts themselves are generally straightforward.
AGK is not typically considered a difficult subject from a conceptual standpoint — the main challenge is the amount of content. Aim to understand the fundamentals, and don’t worry if some details feel unclear at first; regular question-bank practice will help consolidate and clarify the knowledge over time.
Good luck with your AGK studies, and keep training smart!
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