What is the purpose of a weight-on-wheels (WOW) sensor?

• A. To measure engine thrust.
• B. To monitor cabin temperature.
• C. To alert crew to gear turbulence.
• D. To detect when the aircraft is on the ground and enable ground-specific functions such as spoilers and braking logic.

Answer: (D)

Weight-on-wheels sensing provides a signal that indicates when the aircraft’s wheels are in contact with the ground. This lets the aircraft switch from flight mode to ground mode, enabling systems that should work only after touchdown. In practice, that includes ground-specific functions like spoiler deployment and the braking logic (auto-brake, braking rules, and related ground stability aids) that help decelerate and control the airplane on the runway. These functions are not active in the air, so the WOW signal ensures they don’t operate mid-flight. The sensor isn’t related to engine thrust, cabin temperature, or alerts about turbulence.