Definition
Electrical switches mounted on the landing gear struts that sense whether the airplane is on the ground or in flight. When the gear is compressed by the airplane's weight, the switch is in the 'ground' position; when the strut extends after liftoff, the switch moves to the 'air' position. This signal is used by other aircraft systems to enable or disable certain functions depending on whether the airplane is on the ground or airborne.
Plain English
Small switches on the landing gear that tell the airplane whether it is sitting on the ground or flying. They flip one way when the wheels are pressed down by the airplane's weight, and the other way when the airplane lifts off and the gear hangs free.
Context Anchor
Seen in landing gear discussions, especially with retractable landing gear and systems that must know whether the airplane is on the ground.
Derivation
Called 'squat' switches because the gear strut compresses, or 'squats,' under the airplane's weight when on the ground. The strut extending in flight releases the switch.
Why Pilots Care
They block unsafe actions such as gear retraction while on the ground and enable ground-only functions such as thrust reversers or ground spoilers.
Intuition Check
“Squat” does not mean the pilot or airplane is crouching. Here, it means the landing gear is compressed because the airplane’s weight is on the wheels.
Example Sentence 1
The gear handle would not move to the up position on the ground because the squat switches were sensing weight on the wheels.
Example Sentence 2
As the airplane rotated and left the runway, the squat switches opened and allowed the gear to retract normally.