B777 Maintenance Technicians reported failure of the middle rudder power control unit during job; resulted in aircraft damage and a hydraulic leak.
Synopsis
B777 Maintenance Technicians reported failure of the middle rudder power control unit during job; resulted in aircraft damage and a hydraulic leak.
Narrative
We; mechanic Person B and I [Person A]; were in the process of locking out the upper; lower; and middle Power Control Unit (PCU); per job card step X. As I was holding the rudder; right pedal; to the right. Person B was at the rudder station. He was able to attach the middle lock on to the middle PCU. As soon as he attached the lock - the aircraft lost power. I frantically communicated to Person B that I lost power to the aircraft and to step away from rudder area. The rudder shot to neutral position. With the middle lock to PCU attached / secured. Person B was safe.I went down to the power unit. Tried to start power to outlet 1. No help. The unit showed some error message. Connected output 2. Got power. Restarted process of right rudder lockout. With hydraulics on. I pressed right rudder pedal. Noticed the whole plane shake. Person B communicated back to me something broke". Now proceeded to install upper and lower PCU locks for middle PCU change. Hydraulics to on. applied right rudder. I heard a loud bang. Person B yelled to shut down. The middle PCU had failed. Suggestions: Positive ground equipment. Unknown at this moment. Pretty shaken up on the incident."
Second reporter narrative
I [Person B] and Person A were assigned to work on this rudder and tab component lubrication job card. while I was up there; I had Person A moved the rudder to the right as I was able to install the first lock to the middle Power Control Unit (PCU). Aircraft lost power as soon as I installed the lock to the middle PCU. Person A communicated with me that he had to go put the power back on in order for us to continue our lube job. As soon as aircraft's power came back on; Person A returned to the flight deck. I instructed Person A to turn hydraulic back on and step on the right-side rudder. as soon as he did that; rudder kicked back to the neutral position and some metal pieces came off from the middle PCU. We both learned that it would be a middle PCU change and we wanted to continue installing the upper and lower PCU locks. We turned on hydraulic again and I witness the PCU failed and caused a hydraulic leak. I told Person A right away to shut down hydraulic.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.