A&P A&P Aircraft Hydraulic & Pneumatic Systems 2 — Questions and Answers
Question 1: In an aircraft pneumatic system, what is the most common source of high-pressure air used for system operation?
- A dedicated electric compressor
- Bleed air tapped from the engine compressor stages (Correct answer)
- A ground air cart only
- The APU generator
Correct answer: Bleed air tapped from the engine compressor stages
Most turbine-powered aircraft pneumatic systems use bleed air extracted from the engine's compressor section as the primary pressure source for flight controls, pressurization, and other pneumatic actuators.
Question 2: What is the function of a pneumatic system's pressure regulator?
- Convert pneumatic pressure to hydraulic pressure
- Reduce high-pressure bleed air to a lower, usable system pressure (Correct answer)
- Store compressed air
- Filter moisture from the air supply
Correct answer: Reduce high-pressure bleed air to a lower, usable system pressure
The pressure regulator reduces the very high pressure of engine bleed air to a lower, controlled pressure suitable for operating pneumatic components without damage.
Question 3: Why is moisture a critical concern in pneumatic systems, especially at high altitudes?
- Moisture increases system pressure
- Moisture can freeze in lines and valves at altitude, causing blockages and system failure (Correct answer)
- Moisture improves lubrication of pneumatic components
- Moisture is only a problem at low altitudes
Correct answer: Moisture can freeze in lines and valves at altitude, causing blockages and system failure
Water vapor in pneumatic lines can freeze at the low temperatures encountered at altitude, blocking orifices, valves, and lines and causing system malfunctions.
Question 4: A hydraulic actuator that holds position under load without continuous fluid flow is best described as a:
- Single-acting actuator
- Double-acting actuator
- Locked (mechanically locked) actuator (Correct answer)
- Hydraulic motor
Correct answer: Locked (mechanically locked) actuator
Mechanically locked actuators (such as those used for landing gear) hold their position through a mechanical lock so they do not require continuous hydraulic pressure to remain extended or retracted.
Question 5: What is the purpose of a debooster valve in an aircraft hydraulic brake system?
- Increase brake pressure for heavy aircraft
- Reduce high system pressure to a lower, controllable pressure at the brake actuators (Correct answer)
- Filter hydraulic fluid before the brakes
- Prevent brake lockup
Correct answer: Reduce high system pressure to a lower, controllable pressure at the brake actuators
A debooster valve reduces the high hydraulic system pressure to a lower pressure suitable for the brake actuators, protecting brake components from overpressure.
Question 6: Which type of hydraulic pump provides a constant flow regardless of system pressure, making it simple but potentially wasteful of energy?
- Variable-displacement pump
- Fixed-displacement (constant-delivery) pump (Correct answer)
- Hand pump
- Air-driven pump
Correct answer: Fixed-displacement (constant-delivery) pump
A fixed-displacement pump delivers a constant volume of fluid per revolution regardless of system demand; excess fluid is bypassed through the relief valve, generating heat in inefficient designs.
A&P A&P Aircraft Hydraulic & Pneumatic Systems 2
In an aircraft pneumatic system, what is the most common source of high-pressure air used for system operation?