A&P A&P - Aircraft and Powerplant Hydraulic and Pneumatic Systems 1 — Questions and Answers
Question 1: What type of fluid is used in most modern commercial aircraft hydraulic systems?
- Skydrol (phosphate ester-based) (Correct answer)
- MIL-H-5606 (mineral oil-based)
- MIL-H-83282 (synthetic hydrocarbon)
- Castor oil-based fluid
Correct answer: Skydrol (phosphate ester-based)
Skydrol, a phosphate ester-based fluid, is used in most modern commercial aircraft because it is fire-resistant.
Question 2: What is the primary function of a hydraulic accumulator in an aircraft system?
- Store pressurized fluid to dampen pressure surges and provide emergency power (Correct answer)
- Filter contaminants from the hydraulic fluid
- Convert hydraulic pressure into electrical energy
- Regulate fluid temperature throughout the system
Correct answer: Store pressurized fluid to dampen pressure surges and provide emergency power
A hydraulic accumulator stores pressurized fluid to dampen pressure surges and provide a reserve for emergency operations.
Question 3: Which component in a hydraulic system prevents pressure from exceeding a safe maximum?
- Relief valve (Correct answer)
- Check valve
- Selector valve
- Priority valve
Correct answer: Relief valve
A relief valve opens automatically when system pressure exceeds the preset maximum, bypassing fluid back to the reservoir.
Question 4: A hydraulic system pressure gauge reads zero with the engine running. What is the MOST likely cause?
- Failed engine-driven pump or broken drive shaft (Correct answer)
- Low fluid temperature
- Accumulator overcharged with nitrogen
- Selector valve stuck in neutral
Correct answer: Failed engine-driven pump or broken drive shaft
Zero pressure with the engine running most likely indicates a failed engine-driven hydraulic pump or its drive coupling.
Question 5: What is the purpose of a hydraulic system's case drain line on a variable-displacement pump?
- Return leakage fluid from the pump housing back to the reservoir (Correct answer)
- Supply fluid to the pump inlet
- Provide a path for emergency fluid bypass
- Cool the hydraulic actuators
Correct answer: Return leakage fluid from the pump housing back to the reservoir
The case drain line returns internal leakage fluid from inside the pump housing to the reservoir to prevent pressure buildup.
Question 6: In a pneumatic system, what component is used to remove moisture from compressed air before it enters system components?
- Air/oil separator or moisture separator (Correct answer)
- Pressure regulator
- Restrictor orifice
- Pneumatic accumulator
Correct answer: Air/oil separator or moisture separator
An air/oil separator or moisture separator removes water and oil from compressed air to prevent corrosion and component damage.
A&P A&P - Aircraft and Powerplant Hydraulic and Pneumatic Systems 1
What type of fluid is used in most modern commercial aircraft hydraulic systems?