A&P Hydraulic and Pneumatic Systems 1 — Questions and Answers
Question 1: What is the primary purpose of a hydraulic system relief valve on an aircraft?
- To filter contaminants from the fluid
- To limit maximum system pressure and prevent overpressure damage (Correct answer)
- To regulate fluid temperature
- To separate air from the hydraulic fluid
Correct answer: To limit maximum system pressure and prevent overpressure damage
A hydraulic relief valve opens at a preset pressure to bypass fluid back to the reservoir, protecting system components from overpressure.
Question 2: Which type of hydraulic fluid is used in most modern transport-category aircraft and is compatible with natural rubber seals?
- MIL-PRF-5606 (mineral-based)
- MIL-PRF-83282 (synthetic hydrocarbon)
- Skydrol (phosphate ester) (Correct answer)
- Ethylene glycol-based fluid
Correct answer: Skydrol (phosphate ester)
Skydrol and similar phosphate ester fluids are used in most transport-category aircraft and require synthetic seals, not natural rubber.
Question 3: What color is MIL-PRF-5606 mineral-based hydraulic fluid?
- Blue
- Purple
- Red (Correct answer)
- Clear
Correct answer: Red
MIL-PRF-5606 is red-dyed mineral oil hydraulic fluid, commonly used in general aviation aircraft.
Question 4: In an aircraft hydraulic system, what is the function of the accumulator?
- Filter the hydraulic fluid before it reaches actuators
- Store pressurized fluid to supplement the pump during peak demands (Correct answer)
- Sense system pressure and signal the pump to start
- Cool hydraulic fluid returning from actuators
Correct answer: Store pressurized fluid to supplement the pump during peak demands
An accumulator stores a reserve of pressurized hydraulic fluid to supplement pump output during high-demand operations and damp pressure surges.
Question 5: What is the purpose of a hydraulic power pack (self-contained unit) on light aircraft?
- It replaces the engine-driven pump with an electric motor-driven pump, reservoir, and valve assembly (Correct answer)
- It stores emergency hydraulic fluid in case of a main system leak
- It converts hydraulic pressure to pneumatic pressure
- It provides a backup source of electrical power
Correct answer: It replaces the engine-driven pump with an electric motor-driven pump, reservoir, and valve assembly
A hydraulic power pack integrates an electric pump, reservoir, selector valve, and actuator into one self-contained unit, commonly used for retractable landing gear on light aircraft.
Question 6: When servicing an aircraft pneumatic system's air bottle, what must a technician verify before removing the filler valve?
- That the aircraft is on jacks
- That the bottle pressure has been bled to zero (Correct answer)
- That the engine is running to maintain pressure
- That the hydraulic system is isolated
Correct answer: That the bottle pressure has been bled to zero
The high-pressure air bottle must be fully depressurized to zero before removing any fittings or the filler valve to prevent a dangerous pressure release.
A&P Hydraulic and Pneumatic Systems 1
What is the primary purpose of a hydraulic system relief valve on an aircraft?