Definition
A landing gear position-sensing switch assembly, also called a squat switch or weight-on-wheels switch, mounted on a landing gear strut. When the aircraft is on the ground, the strut compresses and the two arms of the assembly are squeezed together, mechanically actuating an electrical switch. When the aircraft lifts off, the strut extends and the arms open, changing the switch state. This signal is used by other aircraft systems to know whether the aircraft is on the ground or in flight.
Plain English
A switch on the landing gear that tells the aircraft whether it is sitting on the ground or flying. It works by being pinched closed when the gear leg compresses under the weight of the aircraft, and opening up again once the wheels leave the runway.
Context Anchor
Seen in aircraft maintenance when a nut is damaged, frozen in place, or unsafe to remove by ordinary wrenching.
Derivation
Named after the kitchen tool used to crack nuts, which works by pinching two arms together. The landing gear assembly looks and acts the same way: the two arms of the switch are squeezed together when the strut compresses under the aircraft's weight.
Why Pilots Care
Many aircraft systems rely on the squat switch signal to operate safely and correctly. A faulty nutcracker switch can cause the gear handle to stay locked when it should release, can prevent retraction after takeoff, or can confuse systems like anti-skid, autothrottle, and pressurization. Knowing what this switch is and where it lives helps with troubleshooting unexpected system behavior on the ground or just after lift-off.
Intuition Check
Do not think of kitchen nutcrackers here. In aircraft maintenance, nutcrackers are tools for splitting metal fastener nuts, not food shells.
Example Sentence 1
After landing, the nutcrackers compressed and signaled the gear control system that the aircraft was now on the ground.
Example Sentence 2
Using nutcrackers allowed the mechanic to remove the seized fastener without damaging the surrounding structure in the tight avionics bay.