Which switch tells the LGCU the gear is down?

• A. A microswitch on each gear draglink
• B. A proximity switch on each gear door
• C. A pressure sensor on the hydraulic line
• D. An optical sensor in the gear well

Answer: (A)

Powerful, reliable end-state signaling is what the LGCU relies on to know the gear is down. A microswitch mounted on each gear draglink is designed to be actuated only when the gear is fully extended and locked. As the draglink moves with the gear, the switch provides a definite, hard sensor input to the LGCU that the gear is in the down position. This direct end-of-travel indication is the most accurate and robust way to confirm gear-down status, which is critical for the system to sequence the doors and hydraulics correctly.

Proximity switches on the gear doors would only tell you about the door position, not the actual gear position, so you could get a mismatch if a door is open while the gear isn’t fully down. A pressure sensor on the hydraulic line could reflect changes in hydraulic pressure rather than the gear’s real position and might mislead the system during partial extensions or leaks. An optical sensor in the gear well could be unreliable in dirty, oily, or cramped environments and still not guarantee the gear is fully down and locked.