Regional Jet 200 ER/LR (CRJ200)
Maintenance Powerplant; Maintenance Airframe
Training / Qualification; Confusion; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway
General Maintenance Action
Manuals; Procedure
The event happened at the run-up area while we were completing operational tests following maintenance on JB2 and JB3 junction boxes. Testing procedures for thrust reverser control systems outlined in CRJ200 AMM 24-01-02 and 24-01-03 indicated the test would be performed while simulating wheel speed movement. Our interpretation of the procedure was we could either simulate wheel speed movement or use actual wheel speed; for example; while taxiing. We chose to use actual wheel speed since that was the current configuration of the aircraft. While rolling with engines at idle; the test procedure had us open 3 circuit breakers then operate the thrust reverser to verify certain messages would illuminate on EICAS. Once the breakers were pulled; nose wheel steering and brakes were inoperative. At that point; the aircraft began to veer left towards the edge of the taxiway. I was sitting right seat and immediately reset the circuit breakers so the Pilot in Command (PIC) could regain control of the aircraft. By the time I had the circuit breakers reset and systems came back online; we had already rolled off the edge of the taxiway into a shallow ditch where the left main sank in 6 inches of mud bringing the aircraft to a stop.The testing procedure did not say actual wheel speed could not be used.Instructions to perform maintenance provided by the manufacturer of any aircraft should be specific on what can and cannot be done during testing or repairs of any kind. In the event the instructions are not clear and there is any doubt on actions that should be taken; personnel performing the task should stop immediately and ask for help or contact the manufacturer to gain a better understanding of the task at hand.
[Report narrative contained no additional information.]
While performing a retest; mechanics pulled three different circuit breakers which affected the nose wheel steering and the brakes which caused the loss of control and caused the aircraft to run off the taxiway into the mud.