Air Traffic Control Fully Certified; Flight Crew Instrument; Flight Crew Commercial; Flight Crew Flight Instructor
Flight Crew Last 90 Days 80; Flight Crew Total 700; Flight Crew Type 550
Aircraft Equipment Problem Less Severe; Conflict Ground Conflict; Less Severe; Ground Event / Encounter Loss Of Aircraft Control; Ground Event / Encounter Object; Ground Excursion Taxiway
Aircraft Aircraft Damaged; Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Aircraft
After starting the engine and during our pre-taxi check at ZZZ Airport; the student pilot and I performed a brake check. The student occupied the pilot seat; and myself in the co-pilot seat. We both confirmed positive brake pressure in each pedal. We contacted Ground Control and received taxi clearance to taxi to runway XX via taxiway A. During the taxi from the FBO ramp to taxiway A; we had positive brake pressure. As we approached the end of taxiway A for runway XX; we started to maneuver the aircraft to the left so that we could make a 180-degree turn into the wind in order to perform an engine run-up. As we started to go left; the student pilot stated that he did not have pressure on the right brake. I took control of the aircraft and confirmed that I did not have pressure or authority in the right brake. I applied full right rudder for nose wheel steering and full right brake and the airplane continued straight ahead. At this time I determined the plane was going to depart the taxiway surface; and promptly pulled the mixture to idle cut-off to stop the engine running. I believe that this was the safest thing that I could do to ensure the safety of my student and myself. After that; the airplane departed the taxiway and the left main landing gear came into contact with a taxiway light.
Flight Instructor reported the right brake failed while the student was maneuvering for run-up and aircraft departed the taxiway.