Coupling and Uncoupling
Coupling and Uncoupling is tested through ordered steps and the reason behind each one. Examiners want evidence that you can couple a tractor and trailer without relying on sound alone, and uncouple without dropping a trailer or tearing off air lines. The sequence matters as much as the individual check.
Coupling sequence
Inspect the kingpin, apron, and fifth wheel. Open the jaws and confirm the locking mechanism moves freely. Back straight and slowly in low gear until the jaws close around the kingpin. Set the trailer parking brakes before the tug test. Pull forward gently against the brakes; if the trailer moves, the kingpin is not locked. Confirm the jaws are closed, the locking lever is down, and the safety latch is engaged. Connect the red emergency line to red and the blue service line to blue, then the electrical cord. Raise the landing gear fully, check lights and trailer brakes, and release the trailer parking brake only after all checks pass.
Uncoupling sequence
Park on firm, level ground. Apply the tractor parking brake and chock the trailer wheels. Lower the landing gear to the ground and confirm it bears weight. Disconnect the electrical cord and air lines, and close the glad-hand couplers. Pull the fifth-wheel release handle, then pull forward slowly. Stop and check that the trailer is stable before driving away.
Worked example
During a tug test, the trailer creeps forward. The driver checks the trailer spring brakes and finds them released because the trailer supply valve is closed. Without air, the trailer brakes cannot hold, so the test result is meaningless. Reopen the supply valve, recharge the trailer system, and repeat the test.
Traps
Coupling at a sharp angle; forgetting to chock; pulling the release handle before the landing gear carries weight; leaving the electrical cord stretched or pinched.