A dual air brake system has two separate air brake systems, both controlled by the same set of brake controls. Each system has its own air tanks, hoses, lines, etc. The primary system typically operates the regular brakes on the rear axle or axles. The secondary system operates the regular brakes on the front axle (and possibly one rear axle). If one system loses air pressure, you’ll still be able to stop your vehicle by using the brakes controlled by the other system, but your vehicle’s braking distance will increase, which isn’t good. Better to bring your vehicle to a safe stop and get the brakes repaired.