Maintenance personnel reported during taxi check for brake discrepancy; the aircraft veered to the right while applying brakes and exited taxiway.
Synopsis
Maintenance personnel reported during taxi check for brake discrepancy; the aircraft veered to the right while applying brakes and exited taxiway.
Narrative
Sent on a field trip to repair an aircraft; 1+2 MLG (Main Landing Gear) temps out of range with # 3+4. During troubleshooting found air in #3 & #4 brake assy which could cause uneven brake press and temp readings. Pilots requested a maintenance taxi before acceptance. I rode right seat as I has previously held run/taxi previously and felt comfortable but had lapsed. Person A was left seat as he was the only taxi/run qualified AMT. He took extra precaution and asked for an escort as he was uncomfortable with taxiing in an unfamiliar airport. He followed the escort and was checking the brakes to feel the operation. At one point he braked; the aircraft jerked left then launched to the right almost going into the grass (which we later found out the RT MLG did). Then we heard a loud squealing sound and stopped. The escort informed us the NLG (Nose Landing Gear) was sideways. Fire rescue verified there was no damage hindering travel back to the gate. Person A taxied the aircraft back to the gate. My function was oversight and radios; but was told the escort would be speaking with Person A directly through cell phone. I suspect there was another issue with brake system; or operator error. I can't distinguish at this time. We were pressed for time to release aircraft; and we were out of our comfort zones of what we do routinely. More detailed explanation of what to do after findings. Clearer comms with maintenance control regarding policy.
Second reporter narrative
During normal aircraft taxi while conducting brake test for work performed. Aircraft pulled violently; it caused for aircraft MLG tires #3 & #4 to go off taxiway. It was reported by escort being followed that nose gear was observed horizontal to the trajectory of aircraft. Unsure possible faulty components or system. Aircraft still out of service.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.