Which switch tells the LGCU that the gear is UP?

• A. A proximity switch on each gear door
• B. A microswitch on the draglink
• C. A hydraulic switch on the gear leg
• D. A temperature sensor in the gear bay

Answer: (A)

Position sensing for gear retration relies on door status signals. The LGCU uses proximity switches mounted on each main gear door to detect when the doors are fully closed—this corresponds to the gear being in the up position. When both door switches indicate closed, the LGCU recognizes that the gear is stowed and can complete the retraction sequence and lock in that state. This method is reliable because it directly reflects the actual physical position of the gear doors, which is the last moving part to reach the up condition, and it provides redundancy with two switches.

A microswitch on the draglink would indicate linkage position but isn’t the direct indicator of whether the gear is up, and could be out of sync with door or gear status. A hydraulic switch would only sense pressure, not gear or door position, and a temperature sensor in the gear bay doesn’t provide a meaningful signal about whether the gear is extended or retracted.