SR20
Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 75; Flight Crew Total 1160; Flight Crew Type 130
Human-Machine Interface; Situational Awareness; Training / Qualification
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway
Aircraft Aircraft Damaged; General Flight Cancelled / Delayed
Aircraft; Human Factors
After a normal landing we exited the runway. The student had trouble tracking the centerline of the runway as we taxied south to do another takeoff and he said that the plane was pulling to the left. I took the controls and confirmed that yes it did seem to be pulling some so [we decided] we would return to our home base; and have the Mechanic take a look. We turned onto taxiway C2 to enter the runway when the student said his brakes had totally failed. I jumped onto the controls on my side and got the plane stopped just as we were leaving the taxiway. The left main and nose wheel were in the mud although we had stopped 15-20 feet before we would have impacted a taxiway sign. We shut down the plane; got out and observed the right main smoking and saw small flames. I grabbed the fire extinguisher and attempted to put out the flames. It took care of most of it; but required additional retardant from the fire extinguisher supplied by the ground person that showed up to assist. The brake had failed and was leaking fluid; which had ignited due to the heat.So; everyone please check your extinguishers to make sure they are usable and full. You never know when you may need them. Also; if your aircraft is pulling some; it might be best to stop sooner and get out for a physical inspection.
The instructor pilot of a taxiing SR-20 assumed control from his student and was able to bring the aircraft to a stop when the brakes failed.  The left main and nose gears came to rest in the mud to the side of the taxiway and leaking brake fluid had ignited due to the heat of the brakes. The flames were extinguished with fire retardant.