Definition
A mechanical or electrical device that prevents a system from operating until a specific condition is met, typically used on retractable landing gear to prevent inadvertent gear retraction while the aircraft is on the ground. The most common example is the squat switch (also called a weight-on-wheels switch) mounted on a landing gear strut, which keeps the gear-up circuit open whenever the strut is compressed by the airplane's weight.
Plain English
A switch that blocks something from happening unless it's safe. On the landing gear, it stops the wheels from folding up while the airplane is still sitting on them.
Context Anchor
Seen in retractable landing gear systems, especially when learning how the airplane prevents an accidental gear retraction on the ground.
Why Pilots Care
It stops unintended activation that could damage the aircraft or create a hazard while on the ground.
Intuition Check
Do not read safety switch as just any switch used for safety. In this context, it usually means the landing gear protection switch that senses whether the airplane is on the ground.
Example Sentence 1
The landing gear safety switch on the left main strut prevents the gear from retracting while the airplane's weight is on the wheels.
Example Sentence 2
During the before-takeoff check the pilot confirmed the safety switch was functioning so the starter would only engage on the ground.