FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsMedium
An engine-driven hydraulic pump on a light twin begins producing a loud whining/growling noise and erratic pressure fluctuations shortly after the reservoir fluid level was found to be low. A borescope inspection later reveals pitting and erosion on the internal pump gears. What condition most likely caused this damage?
- APump cavitation from fluid starvation at the pump inlet
- BExcessive accumulator precharge pressure
- CContamination from a ruptured filter bypass valve
- DThermal expansion of fluid in an isolated line section
Show answer & explanationAnswer & explanation
Correct answer: A. Pump cavitation from fluid starvation at the pump inlet
When reservoir fluid is low, the pump inlet cannot receive an adequate supply of fluid, causing dissolved air and vapor pockets to form and collapse violently at the pump inlet — a condition called cavitation. This produces characteristic noise, pressure fluctuations, and erosion/pitting damage to pump internal components.
Why the other options are wrong
- B. Excessive accumulator precharge affects accumulator cycling, not pump gear erosion.
- C. Filter bypass contamination could cause wear but does not typically produce the whining noise tied to low reservoir level.
- D. Thermal expansion affects isolated line sections, not pump inlet starvation or gear pitting.
Hydraulic Pump Cavitation
A condition where insufficient fluid supply at the pump inlet causes vapor bubbles to form and collapse, producing noise, pressure fluctuations, and pump damage.
- Caused by low reservoir fluid, clogged inlet screen, or excessive fluid viscosity
- Produces distinctive whining/growling noise
- Leads to pitting/erosion of pump internal components over time
Memory trick: Cavitation = pump gasping for fluid, bubbles popping like tiny explosions inside