When performing a pre-trip air supply inspection, what is the first action to take?

Setting the brake is essential as the first action during a pre-trip air supply inspection because it ensures the vehicle remains stationary and secure while the inspection is being conducted. This step is critical for safety, as it prevents any unintended movement of the vehicle, which could lead to accidents or injuries during the inspection process.

By securing the vehicle with the brake, the inspector can confidently proceed with checking the air supply system and performing other necessary inspections without the worry of the vehicle rolling or shifting unexpectedly. This foundational step allows the inspector to focus on evaluating the air supply components, such as tanks, lines, and connections, with the assurance that the vehicle is immobilized.

Other actions, while important, are secondary to establishing a safe working environment. For example, turning on the master switch comes after ensuring the vehicle is secured, and pumping the brakes is typically done to check for proper air pressure and functionality after safety measures are taken. Checking tire pressure is also important, but it is unrelated to the initial steps of verifying the air supply system functionality in a stationary vehicle setup.