C182 Flight Instructor with student reported taxiway excursion on taxi out for take-off.
Synopsis
C182 Flight Instructor with student reported taxiway excursion on taxi out for take-off.
Narrative
My student and I completed our preflight before our training mission. The preflight included checking the brakes and general condition of the plane visually. No issues were found during the preflight inspection. After our after-start checklist; we started the engine and flashed the lineman with our taxi lights to indicate we were ready to taxi. We called the Ground and got our clearance. As we started taxiing; my student said that the airplane was not turning sufficiently to the right. This was the student's second flight; so I helped a little bit; and we could turn off the ramp without a problem. I told the student to complete the brake check once we were out of the ramp (very narrow ramp). Once on the taxiway; we had another right turn; and the plane did not want to turn. We applied the brake; and it did not turn. At this moment; I took the plane and used the right rudder and brake; and we did not turn. We slowly departed the taxiway (only like 3 kts.) and stopped there. We notified the Ground and said we would need to shut down. We were pulled to the ramp by the FBO team. The aircraft did not suffer any damage. Good thing we were taxiing very slowly; which I have been emphasizing to my customers. My only lesson learned was probably to do the brake check earlier as soon as we started taxing to the ramp. I always do this; but this time we had a jet next to us that was ready to taxi; and we did not want to block the jet.
Second reporter narrative
Began taxi of aircraft from parking spot at the FBO. Airplane seemed difficult to turn right but attributed this to my inexperience and eventually was able to do so. Popped the brakes after first movement to confirm operation which appeared normal; then continued taxi. Once off the apron and on taxi way was unable to complete right turn to continue in appropriate direction on taxiway. Right rudder was not turning nose wheel enough; and idle power was enough to pull the airplane forward to edge of pavement even while a attempting to brake the aircraft. Nose wheel left the taxiway pavement. Continued to try to apply brakes to attempt to prevent this but found them less effective than usual and right rudder pedal went to floor. Called Tower; eventually the right main landing gear also left the pavement as brakes were not holding as normal. Tower sent FBO crew; we shut down the engine and moved the aircraft back to the pavement with the assistance of FBO crew. No damage to aircraft; all of this occurred very slowly. Airplane was then towed to maintenance facility on a dolly; root cause was found to be twofold - over pressurization of nose gear strut at recent annual; causing the steering mechanism to be overridden by the nose wheel centering system and failure of right brake system due to right brake wear and fluid loss; also missed at annual inspection. This combined failure resulted in inability to maintain expected direction of aircraft during taxi phase and also inability to stop as expected to prevent the airplane leaving the runway; the only functional brakes also served to turn the airplane in the wrong direction (left rather than the necessary right turn). Also having left brakes functional made the brake check at initial taxi appear to have confirmed brakes operated correctly; its possible there was just enough pressure in the system at that time as well. Overall this was a difficult situation to diagnose at the time given multiple failures. Also odd was that the airplane was operated normally just the day before. The brake fluid likely leaked out completely overnight; but the gas strut in the nose wheel would have been just as pressurized before. I cannot explain why this would have been fine the day before; but this was confirmed as the cause - after depressurizing the gas strut; the airplane taxis normally with rudder pedals turning the nose wheel.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.