aircraft pneudraulic systems mechanic Interview Questions and Answers

1. What is the difference between a pneumatic and a hydraulic system?

   • Answer: Pneumatic systems use compressed air as the working fluid, while hydraulic systems use incompressible liquids (usually oil). Pneumatic systems are generally simpler and less expensive but offer lower power density and are more susceptible to leaks and temperature variations. Hydraulic systems provide higher power density, better control, and are less affected by temperature changes, but are more complex and expensive.

2. Explain Pascal's Law and its relevance to hydraulic systems.

   • Answer: Pascal's Law states that pressure applied to a confined fluid is transmitted equally and undiminished in all directions throughout the fluid. This is fundamental to hydraulic systems because it allows a small force applied to a small area to generate a much larger force on a larger area, enabling mechanical advantage.

3. Describe the components of a typical aircraft hydraulic system.

   • Answer: Typical components include a hydraulic pump (providing pressure), reservoir (storing fluid), pressure relief valve (protecting against overpressure), selector valves (directing fluid flow), actuators (linear or rotary movement), filters (removing contaminants), and lines/hoses (carrying the fluid).

4. What are the different types of hydraulic pumps used in aircraft?

   • Answer: Common types include gear pumps (simple, relatively low pressure), vane pumps (higher pressure than gear pumps), and piston pumps (highest pressure, most efficient but also most complex).

5. Explain the function of a hydraulic accumulator.

   • Answer: A hydraulic accumulator stores pressurized hydraulic fluid, providing a reserve of energy for emergency operation or to smooth out pressure fluctuations. They can also absorb shock loads.

6. What are the common types of hydraulic fluid used in aircraft?

   • Answer: Common types include phosphate esters (e.g., Skydrol) and mineral-based oils. The choice depends on the aircraft and system requirements.

7. How do you check the hydraulic fluid level?

   • Answer: The procedure varies depending on the aircraft type and system design. Generally, it involves locating the reservoir dipstick or sight glass and checking the fluid level against the appropriate markings, ensuring the aircraft is level.

8. Describe the process of troubleshooting a hydraulic leak.

   • Answer: This involves visually inspecting the system for leaks, checking fluid levels, listening for unusual noises, and using leak detection tools if necessary. The location of the leak will help determine the affected component.

9. What safety precautions should be taken when working on a hydraulic system?

   • Answer: Always wear appropriate safety glasses and gloves. Ensure the system is depressurized before working on it. Be aware of the potential for high-pressure fluid and the hazards associated with hydraulic fluid. Follow all relevant safety procedures outlined in the maintenance manual.

10. What is a pneumatic system's role in aircraft operation?

    • Answer: Pneumatic systems typically power lower-force applications like actuating brakes, doors, landing gear, and sometimes flight controls. They're often preferred for their simplicity and relatively low maintenance compared to hydraulic systems in these less demanding applications.

11. Explain the function of a pressure regulator in a pneumatic system.

    • Answer: A pressure regulator maintains a constant downstream pressure regardless of fluctuations in upstream pressure or demand. It ensures that pneumatic actuators receive the correct operating pressure.

12. Describe different types of pneumatic actuators.

    • Answer: Common types include pneumatic cylinders (linear motion) and pneumatic motors (rotary motion). Their selection depends on the specific application's force and motion requirements.

13. What is the purpose of a pneumatic filter?

    • Answer: A pneumatic filter removes contaminants such as dust, moisture, and oil from the compressed air to protect pneumatic components from damage and malfunction.

14. How do you troubleshoot a malfunctioning pneumatic system?

    • Answer: Troubleshooting involves systematic checks of air pressure, examining components for leaks, inspecting filters, checking for obstructions in lines, and verifying the proper operation of actuators and control valves. The process often involves using pressure gauges and leak detection tools.

15. What are the safety precautions when working with compressed air?

    • Answer: Always ensure the system is depressurized before working on it. Never point a compressed air nozzle at yourself or others. Wear appropriate eye and hearing protection. Be mindful of the potential for high-pressure air to cause injury.

16. What is a pneudraulic system? Give an example.

    • Answer: A pneudraulic system combines pneumatic and hydraulic systems. For example, a system might use compressed air to initially extend a landing gear strut, then switch to hydraulic pressure for the final extension and locking. This leverages the simplicity of pneumatic for the initial phase and the higher power of hydraulics for final extension.

17. Describe the advantages and disadvantages of using a pneudraulic system.

    • Answer: Advantages include combining the simplicity of pneumatic with the power of hydraulics, potentially reducing weight and complexity compared to using only hydraulics. Disadvantages include increased system complexity and potential for interaction issues between the pneumatic and hydraulic components.

18. How do you maintain a pneudraulic system?

    • Answer: Maintenance involves regular inspections for leaks, checking fluid levels, monitoring air pressure, replacing filters, and conducting functional tests according to the maintenance manual. This requires knowledge of both pneumatic and hydraulic systems.

19. What are the common causes of failure in pneudraulic systems?

    • Answer: Common causes include leaks (in both pneumatic and hydraulic components), component wear and tear, contamination of fluids, incorrect pressure settings, and improper maintenance.

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