What is the purpose of fanning air brakes?

The purpose of fanning air brakes is primarily to decrease air pressure within the brake system. Fanning involves quickly applying and releasing the brake pedal to reduce the overall pressure in the brake lines. This technique is particularly useful in preventing brake fade, a condition where the brakes lose effectiveness due to overheating, which can occur during prolonged stopping or when going downhill.

By decreasing the pressure, the driver can help maintain better control over the braking system, allowing for smoother operation and preventing potential overheating. This method can also serve as a way to release the brakes if they are stuck, ensuring that the vehicle can continue to operate safely.

In contrast, increasing air pressure, improving brake sensitivity, or releasing air from the main reservoir are not objectives of fanning air brakes and do not align with the intended use of this technique.