Operating Air Brakes and Emergency Procedures
Operating Air Brakes and Emergency Procedures
This domain tests smooth, controlled use of service brakes and correct responses to fade, low pressure and failure. Saskatchewan conditions-long grades, ice and heavy loads-make planning and gentle applications exam-relevant.
Core rules
- Apply and release smoothly. Fanning causes pressure loss and heat; a full break followed by full release is generally better than riding the brakes.
- Before a descent, select a lower gear and set a safe target speed. Use engine braking and short service-brake applications to control speed; let brakes cool between applications.
- Watch the air gauge. A warning by 60 psi means stop safely. Spring brakes normally apply around 20–45 psi, so do not wait for automatic application to force a stop.
- If the service brakes fail, downshift progressively, use engine braking, retarders if available, and look for an escape ramp or safe run-off. Do not turn off the engine; you may lose steering assist and retarder function.
- Use the parking brake control for parking, not as a normal service brake. Test spring-brake operation after any repair.
Worked example
A loaded tractor-trailer enters a 7% grade at 90 km/h in 10th gear. The driver brakes repeatedly and speed climbs to 105 km/h; the gauge is steady but the pedal feels soft. Reasoning: repeated applications are overheating the drums, causing fade. Correct response: stop safely if possible, select a lower gear before continuing, cap speed, and use short firm applications with cooling intervals. If he cannot stop, use an escape ramp.
Traps
Do not hold a light continuous brake application down a long grade. Do not pump the pedal to build pressure. Do not use the spring brake as a substitute for a failed service brake at highway speed. Do not ignore a low-pressure warning because the vehicle still moves. Do not downshift after speed is already too high.