Before you back under a trailer, make sure the:

Trailer brakes are locked.. Section 6.4: Ensure trailer brakes are locked so it doesn't roll away.

Before you back under a trailer, make sure the:

ANSWER BREAKDOWN
  • A. Correct. Ensure trailer brakes are locked so it doesn't roll away.
  • B. Incorrect. "Air lines are disconnected." is not correct. Ensure trailer brakes are locked so it doesn't roll away.
  • C. Incorrect. "Landing gear is up." is not correct. Ensure trailer brakes are locked so it doesn't roll away.
  • D. Incorrect. "Engine is off." is not correct. Ensure trailer brakes are locked so it doesn't roll away.