C-402 pilots reported a taxiway excursion due to a landing gear brake malfunction during taxi out.
Synopsis
C-402 pilots reported a taxiway excursion due to a landing gear brake malfunction during taxi out.
Narrative
I was on the left seat as pilot flying on the training flight. We were taxing on taxiway 1 towards runway XX and tried to slow down towards the turn to runway XY hold short line. Suddenly; I found the loss of authority for the right brake which caused me to apply full pressure on both main brakes. Consequently; the airplane pivoted over the left main gear and half of its fuselage including nose and main gear departures to the grass led of taxiway. The same time; my instructor momentarily positioned both engines' mixture control in IDLE position and shut them down. Upon arrival; airport authorities confirmed that our airplane didn't hit any signs or lights or any other obstacles. Both pilots remained on pilot's station all the time with seat belts and shoulder harnesses fastened until the aircraft was towed to maintenance hangar.Cause: Mechanical failure of right main brake. Since no signs of hydraulic fluid leakage were discovered right after airplane was towed to maintenance hangar; I assume the problem is in brake master cylinder.Suggestions: Better quality of maintenance and prompt report of all airplane discrepancies.
Second reporter narrative
[Report narrative contained no additional information.]
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.