Before uncoupling a trailer, what air brake steps help keep the trailer secure?

• A.Leave the trailer supply pushed in so its brakes stay released
• B.Disconnect the lines first and let the trailer roll to the landing gear
• C.Hold the trailer with the hand valve while you uncouple
• D.Apply the trailer parking (spring) brakes by pulling the trailer supply control (or as the procedure directs), then disconnect the lines and stow them safely after the trailer is supported

Why

Spring brakes hold the trailer without depending on air pressure that will be disconnected. Stowing the glad hands off the ground keeps dirt and damage out of seals that must hold pressure on the next trip.

Manual topic: Air Brakes - Trailer Air Brakes · From the Air Brakes practice bank (AB-244).

Practice this subject as a full test

More Tractor Protection Valve, Trailer Brakes & Stab Braking questions

• A trailer breaks away from the tractor and tears both air lines loose. What happens on the tractor side in the first moments?
• What does the trailer air supply control (the red control in the cab) do in normal operation?
• At about what pressure will the trailer air supply control pop out (or the tractor protection valve close) as system pressure falls?
• How do you test the tractor protection valve during an inspection?
• What is the difference between the trailer's emergency (supply) air line and its service air line?