Question
During an applied pressure leakage test on a Class A combination air-brake vehicle (engine off, parking brakes released, service brake fully applied), what is the maximum allowable pressure drop per minute under FMCSA standards, and what failure threshold triggers mandatory out-of-service repair?
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Maximum Allowable Drop: 4 psi in 1 minute. (For single vehicles, it is 3 psi/min; for combination vehicles, 4 psi/min). Static Test Baseline: With brakes released and engine off, the allowable drop is 3 psi/min for combination vehicles (2 psi/min for single). Out-of-Service Threshold: If air loss exceeds 4 psi in 1 minute during the applied test, the vehicle fails inspection and must be repaired before operation. Additionally, if the low air warning signal fails to activate between 55 and 75 psi, or tractor protection valve fails to pop out between 20 and 45 psi, the vehicle is immediately Out of Service.
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