ATL07CA058 · Cessna 172K

The airplane veered off a taxiway and collided with trees after landing. The certified flight instructor (CFI) stated he was conducting a training flight with a new student. A preflight inspection was completed and no anomalies were noted except for a low nose wheel tire which was corrected. They departed the airport and flew north of the airport and completed some air work before returning back to the airport to do some landings. The student pilot made a normal landing to runway 24. The CFI felt the student pilot apply some brakes and informed the student pilot to maintain directional control with the rudder only. The student pilot complied with his instructions, taxied the airplane to the end of runway 24, and turned left onto the taxiway. Another airplane was on the parallel to the runway 24 taxiway. The CFI instructed the student pilot to stop the airplane after clearing the runway. The airplane went further than the CFI wanted it to go and the CFI instructed the student pilot to apply brakes. The CFI applied brakes and the airplane would not stop. The CFI applied the emergency brake and the airplane would not stop. The CFI pulled the mixture to the cut off position and attempted to stop the airplane on the lip of the edge of the taxiway. The airplane did not stop and went down an embankment and collided with some trees. The registered owner and operator of the airplane informed the FAA that the brake system had been serviced a week before the accident by adding brake fluid to the brake system. Review of the airframe logbook revealed no entry had been entered into the logbook pertaining to the servicing of the brake system. A functional test of the brake system was performed by the FAA inspectors who tried to push the airplane with the parking brake engaged. In addition, one FAA inspector got in the airplane's left front seat and applied brakes and then in the right front seat and applied brakes as the other FAA pushed the airplane, and the airplane continued to move in each test. The brake pads and rotors were visually inspected and no anomalies were noted. Visual inspection of the master cylinder found that brake fluid was leaking onto the exterior of the master cylinder components, as evidenced by the staining of dried hydraulic fluid. The carpet near the pilot's (left front seat) rudder pedals were saturated with brake fluid and there were indications of some recently spilled brake fluid which had a reddish color. In addition, brake fluid stains that were brownish in color were observed.

Verbatim NTSB analysis and probable cause from the NTSB dataset