Scenario 139: Spring (parking) brakes apply automatically when air pressure falls to about:

Question: Scenario 139: Spring (parking) brakes apply automatically when air pressure falls to about:

Answer options: ✅ 20–45 psi

• 55–60 psi
• 85 psi
• 100 psi

Correct answer: 20–45 psi

Explanation: Spring brakes apply automatically as pressure drops to roughly 20–45 psi, stopping the vehicle. The correct answer is "20–45 psi". This capacity-fill scenario 139 reinforces the same competency for the airbrake bank and follows the certified explanation standard.