Definition
Electrical switches built into the landing gear system that prevent the gear from being retracted while the airplane is on the ground. The most common type is a squat switch mounted on a main landing gear strut: when the strut is compressed by the airplane's weight, the switch opens the electrical circuit to the gear retraction system, blocking inadvertent retraction on the ground.
Plain English
Switches that stop the wheels from folding up while the airplane's weight is sitting on them. When the airplane is on the ground, the switch is pressed in by the weight and locks the gear-up command out of the system.
Context Anchor
Seen in discussions of retractable landing gear systems and the devices that help prevent accidental gear retraction on the ground.
Why Pilots Care
They prevent the serious hazard of the gear retracting while the airplane is still on the runway or taxiway.
Intuition Check
Safety switches are not usually switches the pilot flips by hand. They are automatic switches in the airplane that respond to a condition, such as weight on the wheels, and allow or prevent an action.
Example Sentence 1
The instructor explained that the safety switches on the main gear struts prevent the gear from retracting while the airplane is still on the runway.
Example Sentence 2
During the takeoff roll the pilot confirmed the safety switches were still closed so the gear could not be accidentally raised.