Final answer:
Pushing to extinguish the CREW SUPPLY OFF pb during preflight would disconnect power to the crew supply system, affecting their equipment and functions.
Step-by-step explanation:
During the preflight, pushing to extinguish the CREW SUPPLY OFF pb would disconnect power to the aircraft's crew supply system.
This would cut off the electrical power supply to the crew's equipment and could potentially impact their ability to communicate and operate certain functions during the flight. It is important to note that the exact consequences may vary depending on the specific aircraft and its systems.