Which hydraulic system can be used to assist manual landing gear extension if the main system fails?

• A. System 2
• B. System 1
• C. System 3
• D. System 4

Answer: (A)

Redundancy in aircraft hydraulics lets a backup circuit take over essential functions when the main system fails. For landing gear, the design includes a path from a secondary or alternate hydraulic system that can still deliver pressure to the gear actuators even if the primary system is lost. This is why the secondary hydraulic system is used to assist manual landing gear extension: it provides the needed hydraulic pressure to extend and lock the gears when the main system isn’t available. The other hydraulic systems don’t feed the gear extension path in this failure scenario, so they can’t provide the same assist.