Which sensors provide confirmation to the LGCU for gear UP and DOWN respectively?

• A. UP: proximity switch on each gear door; DOWN: microswitch on each gear draglink
• B. UP: microswitch on draglink; DOWN: proximity switch on gear door
• C. UP: optical sensor in wheel well; DOWN: pressure sensor on leg
• D. UP: temperature sensor in gear bay; DOWN: proximity switch on gear door

Answer: (A)

The LGCU relies on separate position indicators for up and down so it has a clear, unambiguous signal of the gear state. For an UP confirmation, each gear door has a proximity switch that detects when the door is in the closed position, which occurs when the gear is fully retracted. When all doors are closed, the LGCU receives the up signal.

For a DOWN confirmation, a microswitch on the gear draglink monitors the draglink position as the gear extends. When the draglink reaches its extended, locked position, the microswitch is actuated and the LGCU recognizes that the gear is down.

Using one sensor type for up and a different type for down helps prevent a single sensor fault from misleading the system about the gear state. Other sensor types, like an optical sensor in the wheel well or a pressure/temperature sensor in the gear, aren’t used here because they’re less direct or reliable indicators of the gear’s actual position.