Which of the following is crucial for the safe operation of air brakes?

Maintaining proper air pressure is essential for the safe operation of air brakes because the braking system relies on compressed air to function effectively. Air brakes operate by using air pressure to engage the brake shoes against the brake drum, allowing the vehicle to slow down or stop. If the air pressure is too low, the brakes may not apply effectively, leading to extended stopping distances or total brake failure. Proper air pressure ensures that the brake system operates within its designed parameters, providing reliable and responsive braking performance.

While regular fluid checks, tire rotations, and engine tune-ups are certainly important for overall vehicle maintenance and safety, they do not specifically address the unique requirements of the air brake system. Maintaining the correct air pressure is a critical factor that directly impacts a vehicle's braking ability, making it vital for safe operation.