What devices on the aircraft provide "on ground" indications?

What devices on the aircraft provide "on ground" indications?

• A. Nose gear squat switch and main gear proximity switches
• B. Nose gear height sensor and main gear pressure sensors
• C. Pilot’s eye view only
• D. Ground proximity radar

Answer: (A)

On-ground indications come from sensing the aircraft’s weight on its landing gear and the gear’s position. The nose gear squat switch closes when the nose gear is compressed by the weight of the aircraft on the ground, signaling that the aircraft is on the surface. The main gear proximity switches detect that the main gear is extended and locked, confirming a ground state. These signals are used by systems that behave differently on the ground, such as autobrakes and ground spoilers. Other devices don’t provide a reliable on-ground state: a nose gear height sensor isn’t the standard ground-detection signal, main gear pressure sensors measure hydraulic or tire pressure rather than ground status, pilot’s view isn’t an instrumentation signal, and ground proximity radar is for terrain awareness, not whether the airplane is on the ground.

On-ground indications come from sensing the aircraft’s weight on its landing gear and the gear’s position. The nose gear squat switch closes when the nose gear is compressed by the weight of the aircraft on the ground, signaling that the aircraft is on the surface. The main gear proximity switches detect that the main gear is extended and locked, confirming a ground state. These signals are used by systems that behave differently on the ground, such as autobrakes and ground spoilers. Other devices don’t provide a reliable on-ground state: a nose gear height sensor isn’t the standard ground-detection signal, main gear pressure sensors measure hydraulic or tire pressure rather than ground status, pilot’s view isn’t an instrumentation signal, and ground proximity radar is for terrain awareness, not whether the airplane is on the ground.