Final answer:
The GND CTL pb is a button used during preflight checks in aircraft to test the continuity and functionality of the ground control circuitry. Selecting it during preflight allows the pilot to verify that the ground control circuitry is functioning properly.
Step-by-step explanation:
The GND CTL pb stands for Ground Control Push Button. It is a button used during preflight checks in aircraft.
The purpose of the GND CTL pb is to test the continuity and functionality of the ground control circuitry in the aircraft's electrical system.
During preflight, selecting the GND CTL pb allows the pilot to verify that the ground control circuitry is functioning properly. This is important because the ground control circuitry is responsible for controlling various systems on the aircraft, such as landing gear, flaps, and lights.