Coupling and Uncoupling
The coupling sequence
Coupling a tractor to a trailer is a checklist you should be able to state in order. First, inspect the fifth wheel: jaws open, locking lever in the open position, mounting secure, and the plate greased. Back under the trailer slowly and squarely so the kingpin enters the throat centered. Listen for the click of the jaws closing, then do a tug test: pull forward gently with the trailer brakes set to confirm the kingpin is captured. Next, visually check that the locking lever is in the locked position and the safety latch is engaged. Connect the air lines (red emergency to red, blue service to blue), then the electrical cord, and secure them so they don't drag. Raise the landing gear fully, then release the trailer brakes and do a final pull test.
The uncoupling sequence
Park on level ground, set the tractor parking brake, and chock the trailer wheels if needed. Lower the landing gear until it touches the ground and takes some weight. Disconnect the electrical cord and air lines, and secure them on the tractor. Release the fifth wheel locking lever, pull the tractor forward slowly until the trailer is clear, then stop and confirm the trailer is stable.
Traps in questions
Common distractors: connecting air lines before confirming the fifth wheel is locked; forgetting the tug test; raising the landing gear before the air lines are connected; and releasing the tractor parking brake while still under the trailer. Another trap is color confusion on the air lines. Also watch for answers that skip the safety latch or that say you should rely on the sound of the jaws alone.
Rule of thumb
Remember "Tug, Look, Hook, Crank, Check": tug test, look at the lever and latch, hook up air and electric, crank the landing gear, then final check. For uncoupling, "Brake, Chock, Crank, Disconnect, Release."
Worked example
A question asks what to do immediately after backing under a trailer. The correct next step is the tug test with the trailer brakes set, before connecting any lines or raising the gear.