After backing the tractor under a trailer and confirming the fifth wheel has locked onto the kingpin, what should the driver do next to check that the coupling is secure?

Explanation

The manual's coupling procedure has the driver raise the trailer landing gear just clear of the ground, then pull gently forward with the tractor while the trailer brakes stay locked, which proves the kingpin is really seated in the fifth wheel before the coupling is treated as complete. This is standard driver-training procedure, not a codified federal test, so it is attributed to the manual and topic-scoped to 49 CFR 383.111(c)(1), which names coupling and uncoupling procedures as a required-knowledge area without stating this specific step. Driving away at normal speed is dangerous and not the taught step; testing at driving speed risks a real separation if the coupling failed. Disconnecting the air-lines would defeat the purpose of the check by deliberately removing the air supply the trailer brakes depend on. Leaving the landing gear down describes the opposite of what's required before driving.

Source: 49 CFR 383.111(c)(1)