Free A&P Hydraulic and Pneumatic Systems Questions and Answers — Questions and Answers
Question 1: An aircraft's hydraulic system is equipped with an accumulator. What is a primary function of this component?
- To filter contaminants from the hydraulic fluid.
- To cool the hydraulic fluid after it passes through the pump.
- To store fluid under pressure to supplement the pump and absorb pressure surges. (Correct answer)
- To increase the system pressure above the normal operating pressure for emergency use.
Correct answer: To store fluid under pressure to supplement the pump and absorb pressure surges.
A hydraulic accumulator is a pressure storage reservoir that holds hydraulic fluid under pressure, typically from compressed nitrogen gas. Its primary functions include supplementing the system pump during peak demand, absorbing pressure surges and shocks, and providing a source of emergency pressure in the event of pump failure.
Question 2: During a landing gear retraction sequence, the landing gear doors must open fully before the gear begins to retract. Which type of valve is specifically designed to control the sequence of operations between two branches of a hydraulic circuit?
- Shuttle valve
- Sequence valve (Correct answer)
- Check valve
- Priority valve
Correct answer: Sequence valve
A sequence valve is designed to control the order of operations in a hydraulic circuit. It ensures that one action, such as opening the gear doors, is completed before the next action, such as retracting the gear, begins. A shuttle valve selects between normal and emergency pressure sources, a check valve allows one-way flow, and a priority valve ensures critical systems receive pressure first if system pressure drops.
Question 3: A technician needs to service a large transport category aircraft's hydraulic system which is known to use a phosphate ester-based fluid. Which of the following fluids should be used?
- MIL-H-5606
- Skydrol (Correct answer)
- MIL-H-83282
- MIL-H-6083
Correct answer: Skydrol
Skydrol is a common brand name for phosphate ester-based hydraulic fluid, which is widely used in commercial transport category aircraft due to its fire-resistant properties. MIL-H-5606 and MIL-H-6083 are mineral-based fluids, and MIL-H-83282 is a synthetic hydrocarbon-based fluid; mixing these types is prohibited and can damage system seals and components.
Question 4: While inspecting a brake system hydraulic line, a technician notices a component designed to automatically shut off fluid flow in the event of a sudden, high-rate leak, such as a ruptured line. What is this safety device called?
- A pressure relief valve
- A hydraulic fuse (Correct answer)
- An orifice check valve
- A system bypass valve
Correct answer: A hydraulic fuse
A hydraulic fuse is a safety device that automatically seals off a line if it detects a sudden increase in fluid flow rate or a specific volume of fluid loss, which is indicative of a major leak or ruptured line. This preserves the remaining fluid in the system for other essential components.
Question 5: In many turbine-powered aircraft, the pneumatic system that provides compressed air for air conditioning, pressurization, and anti-icing systems primarily obtains this air from:
- Engine-driven vacuum pumps
- Electrically powered air compressors
- The engine compressor section (bleed air) (Correct answer)
- Ram air scoops connected to storage tanks
Correct answer: The engine compressor section (bleed air)
Turbine-powered aircraft typically use bleed air, which is hot, compressed air extracted from the compressor stages of the engine. This bleed air is the primary source for the pneumatic system, which then conditions and distributes it for various functions like pressurization, air conditioning, and anti-icing.
Question 6: Which of the following is a critical maintenance step for pneumatic de-icing boots to ensure their longevity and proper operation?
- Applying a thick layer of grease to prevent cracking.
- Inflating them to maximum pressure for 24 hours annually to check for leaks.
- Regularly cleaning them with approved agents and applying a rubber preservative. (Correct answer)
- Painting them with standard aircraft paint to protect against UV radiation.
Correct answer: Regularly cleaning them with approved agents and applying a rubber preservative.
Proper maintenance of pneumatic de-icing boots includes regular cleaning with mild soap and water or approved chemical cleaners to remove debris. Additionally, applying manufacturer-approved rubber preservatives (like AgeMaster) protects the neoprene from ozone and weathering, which prevents cracking and extends the service life of the boots.
Free A&P Hydraulic and Pneumatic Systems Questions and Answers
An aircraft's hydraulic system is equipped with an accumulator.
What is a primary function of this component?