What is the first step when performing a pre-trip inspection of an air brake system?

The first step when performing a pre-trip inspection of an air brake system is to check for leaks in the air lines and connections. This step is crucial because air leaks can significantly affect the performance and reliability of the braking system. Ensuring that the air brake system is sealed and functioning properly is foundational to safe vehicle operation.

Identifying and addressing any leaks at the outset helps prevent air pressure loss that could lead to brake failure or reduced braking effectiveness while on the road. It allows the driver to confirm that the system has the adequate air pressure necessary for the brakes to function correctly during the trip.

Other options, while important for overall vehicle safety, do not specifically address the integrity of the brake system itself at the initial stage of inspection. Checking brake fluid levels, testing brake lights, and inspecting tire pressure are parts of a comprehensive vehicle check, but they do not prioritize the air brake system's operational readiness.