What should happen to the air pressure gauge when the foot brake is applied for one minute?

When the foot brake is applied for one minute during a pre-trip inspection, the air pressure gauge should not drop more than specified limits. This indicates that the air brake system is functioning properly and is able to maintain adequate air pressure in the system without excessive leaks.

A minimal drop in air pressure could occur due to normal operation, but any significant drop may indicate leaks or other issues that can compromise the safety of the braking system. Ensuring that the pressure remains stable or only slightly decreases within the acceptable range confirms the integrity of the air brakes and emphasizes the importance of maintenance checks before driving.

The other choices suggest behaviors that either indicate a malfunction or do not align with the expected performance of a properly functioning air brake system.