What can cause brake fade in an air brake system?

Brake fade in an air brake system primarily occurs due to the overheating of brake components resulting from prolonged use. When brakes are applied repeatedly or held for an extended period, the friction generated during braking can lead to elevated temperatures in brake components, such as the brake shoes, drums, or discs. As these components heat up, their ability to generate friction decreases, which reduces the overall braking efficiency.

This phenomenon happens because the materials used in the braking system may have a temperature threshold beyond which they cannot perform effectively. As the temperature rises, factors like brake fluid vaporization or changes in the material properties can occur, further compromising braking performance. Therefore, managing brake temperatures is crucial in preventing brake fade, especially during scenarios that require consistent or repeated braking.

The other choices present factors that may affect braking systems differently but do not directly address the phenomenon of brake fade caused specifically by excessive heat. Inadequate air pressure can lead to other braking issues, insufficient lubrication may cause wear and tear over time, and frequent use of the emergency brake engages a different part of the system altogether. However, overheating from prolonged use is the direct cause of brake fade.