Free Airframe Mechanic Hydraulic and Pneumatic Systems Questions and Answers — Questions and Answers
Question 1: A technician observes that a hydraulic system is operating sluggishly. The system has been serviced recently, and the fluid level in the reservoir is correct. Which of the following is the most likely cause of the issue?
- The system relief valve is stuck open.
- Air has been introduced into the system. (Correct answer)
- The incorrect type of hydraulic fluid was used.
- The ambient temperature is too high.
Correct answer: Air has been introduced into the system.
Air in a hydraulic system is compressible, unlike hydraulic fluid. When air is present, the force applied by the pump will first compress the air before moving the hydraulic fluid, leading to a spongy feel and sluggish operation of actuators.
Question 2: Which type of hydraulic fluid is known for its fire-resistant properties and is commonly used in modern commercial transport aircraft?
- Mineral-based fluid (e.g., MIL-H-5606)
- Vegetable-based fluid
- Phosphate ester-based fluid (e.g., Skydrol) (Correct answer)
- Synthetic hydrocarbon-based fluid (e.g., MIL-H-83282)
Correct answer: Phosphate ester-based fluid (e.g., Skydrol)
Phosphate ester-based hydraulic fluids, such as Skydrol, are widely used in commercial aviation because of their excellent fire-resistant properties, which enhance safety in high-temperature environments like those found near engines and braking systems.
Question 3: In a pneumatic system, what is the primary function of a moisture separator or water trap?
- To cool the compressed air before it enters the system.
- To lubricate the pneumatic components.
- To increase the pressure of the air in the system.
- To remove water vapor and contaminants from the compressed air. (Correct answer)
Correct answer: To remove water vapor and contaminants from the compressed air.
Moisture separators are critical components in pneumatic systems designed to remove water vapor, which naturally condenses out of compressed air. This prevents corrosion of internal components, freezing at high altitudes, and contamination of the system.
Question 4: An aircraft's hydraulic system incorporates an accumulator. What is one of the primary purposes of this component?
- To filter contaminants from the hydraulic fluid.
- To store hydraulic fluid for the pump.
- To dampen pressure surges and supplement the pump's output during peak demand. (Correct answer)
- To cool the hydraulic fluid as it returns to the reservoir.
Correct answer: To dampen pressure surges and supplement the pump's output during peak demand.
An accumulator is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. Its purposes include dampening pressure fluctuations, supplementing the pump's flow during peak demand (like landing gear operation), and providing a source of emergency pressure if the pump fails.
Question 5: A maintenance technician is troubleshooting a pneumatic de-icing boot system that is not inflating properly. The system's engine-driven air pump is verified to be operating correctly. Which of the following components should be inspected next for a possible malfunction?
- The hydraulic reservoir fluid level.
- The system's pressure relief valve.
- The oil-to-fuel heat exchanger.
- The distributor valve or solenoid. (Correct answer)
Correct answer: The distributor valve or solenoid.
In a pneumatic de-icing system, the distributor valve (often operated by a solenoid) is responsible for directing the flow of pressurized air to the de-icing boots in the correct sequence. A malfunction in this valve would prevent the boots from inflating, even if the air pump is working correctly.
Question 6: According to 14 CFR Part 43, Appendix A, which of the following is considered a major alteration to an aircraft's hydraulic system?
- Replacing a hydraulic hose with an identical, approved part.
- Servicing a hydraulic accumulator with nitrogen.
- Changes to the basic design of the hydraulic system. (Correct answer)
- Replacing the seals in a brake master cylinder.
Correct answer: Changes to the basic design of the hydraulic system.
14 CFR Part 43, Appendix A defines major alterations. Changes to the basic design of the fuel, oil, cooling, heating, cabin pressurization, electrical, hydraulic, de-icing, or exhaust systems are specifically listed as major alterations. Simple component replacements or servicing are generally considered maintenance or minor repairs.
Free Airframe Mechanic Hydraulic and Pneumatic Systems Questions and Answers
A technician observes that a hydraulic system is operating sluggishly.
The system has been serviced recently, and the fluid level in the reservoir is correct.
Which of the following is the most likely cause of the issue?