Hydraulics & Pneumatics

Introduction to Hydraulics & Pneumatics

Hydraulics provide mechanical advantage to system components.
There are multiple applications for hydraulic use in aircraft, depending on the complexity of the aircraft.
Test your understanding of Hydraulics & Pneumatics by completing the knowledge quiz, applying your knowledge in the interactive scenario, comparing your performance against the applicable Airman Certification Standards, and concluding with the topic summary to reinforce the key concepts before moving on to the next lesson.

On This Page

Hydraulics & Pneumatics Key Highlights

Hydraulic and pneumatic systems use fluid or compressed gas pressure to operate aircraft components and systems efficiently.
Hydraulic systems commonly power landing gear, brakes, flight controls, flaps, spoilers, and steering mechanisms.
Pneumatic systems may support deicing systems, environmental controls, pressurization, and engine starting functions.
Hydraulic systems operate based on Pascal’s principle, allowing force multiplication through fluid pressure transmission.
Leaks, contamination, overheating, or pressure loss can degrade hydraulic and pneumatic system performance.
Pilots should monitor system pressure, fluid quantity, warning indications, and aircraft handling characteristics for signs of malfunction.
Backup systems and accumulators may provide limited operational capability following hydraulic or pneumatic failures.
Modern aircraft often incorporate multiple redundant hydraulic systems to improve reliability and operational safety.
System malfunctions can significantly affect braking capability, flight control response, landing gear operation, and aircraft handling.
Understanding hydraulics and pneumatics improves systems knowledge, emergency preparedness, and overall flight safety.

Hydraulics & Pneumatics

Hydraulic Systems

Hydraulics is often used on small airplanes to operate:
On large airplanes, hydraulics is used for:
- Flight control surfaces.
- Wing flaps, spoilers.
- And other systems.

Hydraulics & Pneumatics

Hydraulics System Components

Pilot Handbook of Aeronautical Knowledge,
Basic Hydraulic System
A basic hydraulic system consists of: []
- Reservoir.
- Pumps.
- Filters.
- Selector Valves.
- Relief Valve.
- Accumulators.
- Actuators.
Hydraulic Reservoir:
- A mineral-based hydraulic fluid is the most widely used type for small aircraft.
- This type of hydraulic fluid, a kerosene-like petroleum product, has good lubricating properties, as well as additives to inhibit foaming and prevent the formation of corrosion.
- It is chemically stable, has very little viscosity change with temperature, and is dyed for identification.
- Since several types of hydraulic fluids are commonly used, an aircraft must be serviced with the type specified by the manufacturer.
Hydraulic Pumps:
- Hydraulic pumps may be either hand, electric, or engine-driven.
- The hydraulic fluid is pumped through the system to an actuator or servo.
Hydraulic Filters:
- Filters are necessary to keep the fluid clean.
Hydraulic Servos:
- A servo is a cylinder with a piston inside that turns fluid power into work and creates the power needed to actuate an aircraft system.
- Servos can be either single-acting or double-acting, based on the needs of the system.
  - Therefore fluid can be applied to one (single-acting) or both sides (double-acting) of the servo, depending on the servo type.
- A single-acting servo provides power in one direction while a double-acting can provide power in both directions.
Hydraulic Selector Valves:
- The selector valve allows the fluid direction to be controlled.
- This is necessary for operations such as the extension and retraction of landing gear during which the fluid must work in two different directions.
Hydraulic Relief Valves:
- The relief valve provides an outlet for the system in the event of excessive fluid pressure in the system.
- Forces exert equal pressure on system
- Input smaller than output increases force
- Pumps provide system pressure
  - Variable
  - Constant: pressure regulators control pressure
- Pressure gauges provide a way to monitor the system
- Relief valves return fluid to the reservoir
- Check valves used for 1 way flow
Hydraulic Accumulators:
- Accumulators provide shock absorption for 1 time use
Hydraulic Acutators:
- Hydraulic actuators are the mechanical devices that translate hydraulic pressures into mechanical advantages
Pilot Handbook of Aeronautical Knowledge,
Basic Hydraulic System

Hydraulics & Pneumatics

Hydraulics & Pneumatics Interactive Scenario

Interactive Scenario

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Scenario Complete

Hydraulics & Pneumatics

Hydraulics & Pneumatics Knowledge Check

Private Pilot

Core Knowledge Review

Review the foundational knowledge, key concepts, and practical considerations for Hydraulics & Pneumatics.

Foundational Immediate Feedback Answer Explanations

Commercial Pilot

Advanced Application

Apply your knowledge of Hydraulics & Pneumatics to advanced operational scenarios, risk management, and aeronautical decision-making.

Advanced Scenario Based Risk Management

Why Take a Quiz?

Quizzes reinforce key concepts, identify knowledge gaps, and build confidence for real-world decisions in the cockpit. Quiz material is representative of the information provided here and is not based on or sourced from the Federal Aviation Administration test bank.

Hydraulics & Pneumatics

Private Pilot (Airplane) Operation of Aircraft Systems Airman Certification Standards

Objective: To determine whether the applicant exhibits satisfactory knowledge, risk management, and skills associated with safe operation of systems on the airplane provided for the flight test.
References: FAA-H-8083-2 (Risk Management Handbook), FAA-H-8083-3 (Airplane Flying Handbook), FAA-H-8083-23 (Seaplane, Skiplane, and Float/Ski Equipped Helicopter Operations Handbook), FAA-H-8083-25 (Pilot Handbook of Aeronautical Knowledge); POH/AFM.
Note: If K1 is selected, the evaluator must assess the applicant's knowledge of at least three sub-elements
Private Pilot Operation of Aircraft Systems Lesson Plan.

Knowledge 14 ACS Elements

PA.I.G.K1:
Airplane systems, including:
- PA.I.G.K1a:
  Primary flight controls.
- PA.I.G.K1a:
  Secondary flight controls.
- PA.I.G.K1c:
  Powerplant and propeller.
- PA.I.G.K1d:
  Landing gear.
- PA.I.G.K1e:
  Fuel, oil, and hydraulic.
- PA.I.G.K1f:
  Electrical.
- PA.I.G.K1g:
  Avionics.
- PA.I.G.K1h:
  Pitot-static, vacuum/pressure, and associated flight instruments.
- PA.I.G.K1i:
  Environmental.
- PA.I.G.K1j:
  Deicing and anti-icing.
- PA.I.G.K1k:
  Water Rudders (ASES, AMES).
- PA.I.G.K1l:
  Oxygen Systems.
PA.I.G.K2:
Indications of and procedures for managing system abnormalities or failures.

Risk Management 3 ACS Elements

PA.I.G.R1:
Detection of system malfunctions or failures.
PA.I.G.R2:
Management of a system failure.
PA.I.G.R3:
Monitoring and management of automated systems.

Skills 2 ACS Elements

PA.I.G.S1:
Operate at least three of the systems listed in K1a through K1l appropriately.
PA.I.G.S2:
Complete the appropriate checklist(s).

Private Pilot (Helicopter) Operation of Systems Airman Certification Standards

Area of Operation I: Preflight Preparation.
Task G: Operation of Systems.
Objective: To determine the applicant exhibits satisfactory knowledge, risk management, and skills associated with safe operation of systems on the helicopter provided for the flight test.
Note: If K1 is selected, the evaluator must assess the applicant's knowledge of at least three sub-elements.
References: FAA-H-8083-2, FAA-H-8083-21, FAA-H-8083-25; POH/RFM
Private Pilot (Helicopter) Operation of Systems Lesson Plan.

Knowledge 2 ACS Elements

PH.I.G.K1:
Helicopter systems, including:
- PH.I.G.K1a: a. Flight controls, trim, and if installed, stability control
- PH.I.G.K1b: b. Powerplant(s)
- PH.I.G.K1c: c. Main rotor and antitorque systems
- PH.I.G.K1d: d. Transmission and associated drive shafts
- PH.I.G.K1e: e. Fuel, oil, and hydraulic
- PH.I.G.K1f: f. Avionics
- PH.I.G.K1g: g. Landing gear, brakes, steering, skids, or floats, as applicable
- PH.I.G.K1h: h. Electrical
- PH.I.G.K1i: i. Pitot-static, vacuum/pressure, and associated flight instruments
- PH.I.G.K1j: j. Environmental
- PH.I.G.K1k: k. Anti-icing and deicing, including carburetor heat, if applicable
PH.I.G.K2:
Indications of and procedures for managing system abnormalities or failures.

Risk Management 3 ACS Elements

PH.I.G.R1:
Detection of system malfunctions or failures.
PH.I.G.R2:
Management of a system failure.
PH.I.G.R3:
Monitoring and management of automated systems.

Skills 2 ACS Elements

PH.I.G.S1:
Operate at least three of the helicopter's systems listed in K1a through K1k.
PH.I.G.S2:
Complete the appropriate checklist(s).

Private Pilot (Airplane) Systems and Equipment Malfunctions Airman Certification Standards

Objective: To determine whether the applicant exhibits satisfactory knowledge, risk management, and skills associated with system and equipment malfunctions appropriate to the airplane provided for the practical test.
References: FAA-H-8083-2 (Risk Management Handbook), FAA-H-8083-3 (Airplane Flying Handbook), FAA-H-8083-25 (Pilot Handbook of Aeronautical Knowledge); POH/AFM.
Private Pilot (Airplane) Systems and Equipment Malfunctions Lesson Plan.

Knowledge 15 ACS Elements

PA.IX.C.K1:
Causes of partial or complete power loss related to the specific type of powerplant(s).
- PA.IX.C.K1a:
  [Archived].
- PA.IX.C.K1b:
  [Archived].
- PA.IX.C.K1c:
  [Archived].
- PA.IX.C.K1d:
  [Archived].
PA.IX.C.K2:
System and equipment malfunctions specific to the aircraft, including:
- PA.IX.C.K2a:
  Electrical malfunction.
- PA.IX.C.K2b:
  Vacuum/pressure and associated flight instrument malfunctions.
- PA.IX.C.K2c:
  Pitot/static system malfunction.
- PA.IX.C.K2d:
  Electronic flight deck display malfunction.
- PA.IX.C.K2e:
  Landing gear or flap malfunction.
- PA.IX.C.K2f:
  Inoperative trim.
PA.IX.C.K3:
Causes and remedies for smoke or fire onboard the aircraft.
PA.IX.C.K4:
Any other system specific to the aircraft (e.g., supplemental oxygen, deicing).
PA.IX.C.K5:
Inadvertent door or window opening.

Risk Management 4 ACS Elements

PA.IX.C.R1:
Checklist usage for a system or equipment malfunction.
PA.IX.C.R2:
Distractions, task prioritization, loss of situational awareness, or disorientation.
PA.IX.C.R3:
Undesired aircraft state.
PA.IX.C.R4:
Startle response.

Skills 2 ACS Elements

PA.IX.C.S1:
Determine appropriate action for simulated emergencies specified by the evaluator, from at least three of the elements or sub-elements listed in K1 through K5.
PA.IX.C.S2:
Complete the appropriate checklist(s).

Commercial Pilot (Airplane) Systems and Equipment Malfunctions Airman Certification Standards

Objective: To determine whether the applicant exhibits satisfactory knowledge, risk management, and skills associated with system and equipment malfunctions appropriate to the airplane provided for the practical test.
References: FAA-H-8083-2 (Risk Management Handbook), FAA-H-8083-3 (Airplane Flying Handbook), FAA-H-8083-25 (Pilot Handbook of Aeronautical Knowledge); POH/AFM.
Commercial Pilot (Airplane) Systems and Equipment Malfunctions Lesson Plan.

Knowledge 15 ACS Elements

CA.IX.C.K1:
Causes of partial or complete power loss related to the specific type of powerplant(s).
- CA.IX.C.K1a:
  [Archived].
- CA.IX.C.K1b:
  [Archived].
- CA.IX.C.K1c:
  [Archived].
- CA.IX.C.K1d:
  [Archived].
CA.IX.C.K2:
System and equipment malfunctions specific to the aircraft, including:
- CA.IX.C.K2a:
  Electrical malfunction.
- CA.IX.C.K2b:
  Vacuum/pressure and associated flight instrument malfunctions.
- CA.IX.C.K2c:
  Pitot/static system malfunction.
- CA.IX.C.K2d:
  Electronic flight deck display malfunction.
- CA.IX.C.K2e:
  Landing gear or flap malfunction.
- CA.IX.C.K2f:
  Inoperative trim.
CA.IX.C.K3:
Causes and remedies for smoke or fire onboard the aircraft.
CA.IX.C.K4:
Any other system specific to the aircraft (e.g., supplemental oxygen, deicing).
CA.IX.C.K5:
Inadvertent door or window opening.

Risk Management 4 ACS Elements

CA.IX.C.R1:
Checklist usage for a system or equipment malfunction.
CA.IX.C.R2:
Distractions, task prioritization, loss of situational awareness, or disorientation.
CA.IX.C.R3:
Undesired aircraft state.
CA.IX.C.R4:
Startle response.

Skills 2 ACS Elements

CA.IX.C.S1:
Determine appropriate action for simulated emergencies specified by the evaluator, from at least three of the elements or sub-elements listed in K1 through K5.
CA.IX.C.S2:
Complete the appropriate checklist(s).

Sport Pilot (Airplane) Systems and Equipment Malfunctions Practical Test Standards:

Source: FAA-S-8081-29A, Section 1 - Sport Pilot Airplane.
Task: Systems and Equipment Malfunctions (ASEL and ASES).
References: FAA-H-8083-3; AFM/POH.
Objective: To determine that the applicant demonstrates the required knowledge and appropriate response to systems and equipment malfunctions.
Sport Pilot (Airplane) Systems and Equipment Malfunctions Lesson Plan.

Objective Elements 3 PTS Elements

SP.1:
Exhibits knowledge of the elements related to system and equipment malfunctions appropriate to the airplane provided for the practical test.
SP.2:
Evaluates the situation and takes appropriate action for simulated emergencies appropriate to the airplane provided for the practical test for at least three of the following:
1. Partial or complete power loss.
2. Engine roughness or overheat.
3. Carburetor or induction icing.
4. Loss of oil pressure.
5. Fuel starvation.
6. Electrical malfunction.
7. Vacuum/pressure and associated flight-instrument malfunctions.
8. Pitot/static malfunction.
9. Flap malfunction.
10. Inoperative trim.
11. Inadvertent door or window opening.
12. Smoke, fire, or engine-compartment fire.
13. Flight-control malfunction.
14. Ballistic recovery system malfunction, if applicable.
15. Any other emergency appropriate to the airplane.
SP.3:
Follows the appropriate checklist or procedure.

Hydraulics & Pneumatics

Hydraulics & Pneumatics Conclusion

Each system incorporates different components to meet the individual needs of different aircraft.
More advanced aircraft tend to utilize higher pressurization in their system to simplify the engineering and reduce weight.
Still looking for something? Continue searching:

Hydraulics & Pneumatics

Hydraulics & Pneumatics

Introduction to Hydraulics & Pneumatics

Hydraulics & Pneumatics Key Highlights

Hydraulic Systems

Hydraulics System Components

Hydraulic Reservoir:

Hydraulic Pumps:

Hydraulic Filters:

Hydraulic Servos:

Hydraulic Selector Valves:

Hydraulic Relief Valves:

Hydraulic Accumulators:

Hydraulic Acutators:

Hydraulics & Pneumatics Interactive Scenario

Interactive Scenario

Scenario Complete

Hydraulics & Pneumatics Knowledge Check

Core Knowledge Review

Advanced Application

Why Take a Quiz?

Private Pilot (Airplane) Operation of Aircraft Systems Airman Certification Standards

Private Pilot (Helicopter) Operation of Systems Airman Certification Standards

Sport Pilot (Airplane) Operation of Systems Practical Test Standards:

Commercial Pilot (Airplane) Operation of Systems Airman Certification Standards:

Private Pilot (Airplane) Systems and Equipment Malfunctions Airman Certification Standards

Commercial Pilot (Airplane) Systems and Equipment Malfunctions Airman Certification Standards

Sport Pilot (Airplane) Systems and Equipment Malfunctions Practical Test Standards:

Hydraulics & Pneumatics Conclusion

Hydraulics & Pneumatics References