What is the primary cause of brake failure in air brake systems?

Answer: B — Insufficient air pressure due to leaks

The primary cause of brake failure in air brake systems is insufficient air pressure due to leaks. Air brake systems rely on a stable and adequate supply of compressed air to operate effectively. When there are leaks in the system, whether in the air lines, fittings, or components, the air pressure can drop below the necessary threshold. This insufficient pressure can prevent the brakes from engaging properly, leading to a potential failure when attempting to stop the vehicle. Furthermore, air brake systems include various safety features like spring brakes that automatically engage when air pressure becomes critically low. This automatic engagement is designed to prevent complete brake failure, highlighting just how vital maintaining air pressure is in the system overall. Maintaining the integrity of the air lines and ensuring there are no leaks are crucial for the safe operation of vehicles equipped with air brakes.