In what order should the airlines be connected when coupling a tractor to a semi-trailer?

When coupling a tractor to a semi-trailer, it is essential to follow proper procedures to ensure safety and functionality. The correct order involves backing under the trailer before connecting the airlines, and this is particularly important if the trailer is equipped with spring brakes.

When the king pin is securely hooked, it allows the tractor to safely support the weight of the trailer. At this point, if the trailer is fitted with spring brakes, it’s crucial to connect the airlines immediately to release those brakes. This ensures that the trailer can roll freely once the tractor is properly coupled and ready to move.

The sequence of operations is vital for preventing accidents and ensuring the safe operation of the vehicle. Coupling the airlines properly also helps in maintaining brake system integrity, vital for the safe operation of the tractor-trailer on the road. Thus, ensuring the correct order of connecting the airlines after backing under the trailer and hooking the king pin is essential for a secure and operational connection.