AM Hydraulic & Pneumatic Systems Flashcards

What is the purpose of a hydraulic fuse in an aircraft system?

Answer: Automatically shut off flow when excessive flow rate indicates a leak

A hydraulic fuse senses an abnormally high flow rate (indicating a downstream rupture or leak) and closes automatically to isolate the failed section and conserve fluid.

Before performing maintenance on an aircraft hydraulic system, what is the first action a technician must take?

Answer: Depressurize the system and verify zero pressure

The system must be fully depressurized and pressure verified at zero before opening any hydraulic line to prevent fluid injection injury or component ejection.

What causes hydraulic fluid to appear milky or foamy?

Answer: Water contamination

Water contamination causes hydraulic fluid to appear milky or foamy due to emulsification, which degrades lubrication and can cause corrosion and ice formation.

Which pneumatic system component removes moisture from compressed air before it enters the distribution system?

Answer: Air dryer/moisture separator

An air dryer or moisture separator removes water vapor from compressed air to prevent corrosion, ice formation, and valve freezing in the pneumatic distribution system.

What is the correct procedure when mixing different brands of the same type of hydraulic fluid (e.g., Skydrol 500B-4 and Skydrol LD-4)?

Answer: Check with the aircraft manufacturer's CMM before mixing

Even similar-type hydraulic fluids can have additive packages that interact adversely, so the aircraft manufacturer's Component Maintenance Manual must be consulted before mixing brands.

What condition does a hydraulic system ground test must verify before return to service after seal replacement?

Answer: No external leaks at operating pressure and correct actuator travel

A post-maintenance ground test must confirm no external leaks at full operating pressure and verify that all affected actuators move through their correct range of travel.