What precaution should be taken when applying air brakes on a steep slope?

Answer: A — Engage the parking brake to control the vehicle

Engaging the parking brake when applying air brakes on a steep slope is crucial for maintaining control of the vehicle. The parking brake acts as an additional safety measure that helps to prevent the vehicle from rolling backward or gaining excessive speed while descending. This is particularly important because air brakes alone may not provide sufficient holding power, especially on a steep gradient where gravitational forces can overcome the braking system. By engaging the parking brake, you create a secondary system that can assist in maintaining control of the vehicle and ensuring a safe descent. While reducing engine RPM, switching to a lower gear, or even turning off the engine might seem like methods to assist in controlling the vehicle’s speed, they do not provide the same level of security as properly engaging the parking brake. In this context, relying solely on these alternatives could increase the risk of losing control on a steep slope. Thus, engaging the parking brake is a vital precaution to ensure safety while navigating steep descents.