Inspection of Combination Vehicles: Coupling System, Air Lines, and Landing Gear
This domain tests the combination-specific walk-around: the fifth wheel and kingpin, the air and electrical connections, and the landing gear - the items that fail and drop trailers.
Fifth wheel and kingpin
Jaws open, jaws and plate greased, mounting bolts tight, no cracks in the plate or its mount, release lever locked with the safety latch engaged. The kingpin should be straight and unworn, and the trailer apron uncracked. On a sliding fifth wheel, confirm the locking pins are seated.
Air lines and electrical
A tractor-semitrailer has two lines: service (blue) and emergency/supply (red). Crossed lines mean no trailer brakes or a trailer that will not release. Glad-hand seals must be present and uncracked. Lines need enough slack for a full turn without dragging, chafing, or catching on the catwalk. The electrical cord must be fully plugged and secure, with all trailer lights working.
Landing gear
Fully raised, both legs straight, sand shoes present, and the crank handle secured in its holder - not left hanging to catch on tires or the road.
Other combination items
Trailer frame, sliding tandem lock pins, mud flaps, tire condition, brake adjustment, door latches, and load securement.
Worked example
Before backing under a 53-ft dry van, you find the fifth wheel's jaws closed and the release lever down. That looks ready, but closed jaws cannot accept a kingpin - the lever must be in the open position with the jaws open and the safety latch free. Backing under with closed jaws leaves the trailer uncoupled, and the first hard brake drops it onto the frame rails.
Traps
- Treating a closed fifth wheel as a locked one.
- Missing the safety latch on the release lever.
- Ignoring a cracked glad-hand seal that leaks only under pressure.
- Leaving the landing gear crank handle hanging.