What should be checked regarding the connections of the main air line?

The correct answer emphasizes the critical importance of ensuring that the connections of the main air line are tight and free from leaks. This is essential for the safe and effective operation of the vehicle's air brake system. Loose connections can lead to a loss of air pressure, which compromises the braking ability and overall safety of the vehicle. Leaks in the air lines can not only reduce brake efficiency but can also create hazards on the road, making it vital for connections to be secure and intact.

Regular checks for tightness and leaks are a standard part of pre-trip inspections. This involves visually inspecting the air lines and using methods, such as soapy water or sound testing, to identify any leaks. If leaks or loose connections are found, they must be repaired before the vehicle is deemed roadworthy. Overall, maintaining a properly functioning air line connection is crucial for preventing potential accidents and ensuring the safe operation of the vehicle.