A driver crosses the air-lines while coupling an older trailer that has no spring brakes. What danger does the AAMVA manual describe?
Combination Vehicles • Free CDL Practice Question
Regulation
AAMVA CDL Manual, Section 6.2.4, p. 6-6
Why This Matters
On an older trailer without spring brakes, a crossed air-line mistake can let a driver pull away with zero trailer brakes once the stored air leaks out, a scenario the manual calls very dangerous. This is exactly why the manual says to always test the trailer brakes before driving, regardless of how the lines appear to be connected.