Narrative:

I am a mechanic for air carrier X airlines. We accomplish the ETOPS preflight check here in ZZZ for air carrier Y airlines. While accomplishing the ETOPS predep check per air carrier Y paperwork; discovered the hydraulic motor generator was showing no indication of volts or frequencys. Talked with the air carrier Y line maintenance controller. He asked if we could troubleshoot this problem further. We advised him we could since we had another 3-4 hours until departure. Discovered the hydraulic motor generator was turning when we accomplished the hydraulic motor generator test; but still no volts and frequencys. All other cockpit indications were normal. After having another conversation with the air carrier Y maintenance controller; he asked us to check for voltage at the 'hydraulic generator AC volt sense' circuit breaker (C846) on the P65 panel. We accomplished this and found that we did have 115 volts when accomplishing the hydraulic motor generator test. Per the aircraft schematic manual; this breaker goes to the right display control unit per 24-28-01 sheet 1. This in turn determined that the right display control unit (M7242) was no good. After again conferring with the air carrier Y maintenance controller; he told me to defer the hydraulic motor generator as inoperative per the MEL since this is what was not working per the ETOPS predep check. After taking a few days off and testing a couple more aircraft; I felt this was not proper. I thought the right display control unit should have been deferred. After more research of the MEL; I do not believe the display control unit can be deferred. Therefore; the aircraft should have been grounded until repaired.

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Original NASA ASRS Text

Title: A B767-400 WAS DISPATCHED IN EXTENDED RANGE OVERWATER OPS WITH THE HYD MOTOR DRIVEN GENERATOR INOP IN CONFLICT WITH THE MEL.

Narrative: I AM A MECH FOR ACR X AIRLINES. WE ACCOMPLISH THE ETOPS PREFLT CHK HERE IN ZZZ FOR ACR Y AIRLINES. WHILE ACCOMPLISHING THE ETOPS PREDEP CHK PER ACR Y PAPERWORK; DISCOVERED THE HYD MOTOR GENERATOR WAS SHOWING NO INDICATION OF VOLTS OR FREQS. TALKED WITH THE ACR Y LINE MAINT CTLR. HE ASKED IF WE COULD TROUBLESHOOT THIS PROB FURTHER. WE ADVISED HIM WE COULD SINCE WE HAD ANOTHER 3-4 HRS UNTIL DEP. DISCOVERED THE HYD MOTOR GENERATOR WAS TURNING WHEN WE ACCOMPLISHED THE HYD MOTOR GENERATOR TEST; BUT STILL NO VOLTS AND FREQS. ALL OTHER COCKPIT INDICATIONS WERE NORMAL. AFTER HAVING ANOTHER CONVERSATION WITH THE ACR Y MAINT CTLR; HE ASKED US TO CHK FOR VOLTAGE AT THE 'HYD GENERATOR AC VOLT SENSE' CIRCUIT BREAKER (C846) ON THE P65 PANEL. WE ACCOMPLISHED THIS AND FOUND THAT WE DID HAVE 115 VOLTS WHEN ACCOMPLISHING THE HYD MOTOR GENERATOR TEST. PER THE ACFT SCHEMATIC MANUAL; THIS BREAKER GOES TO THE R DISPLAY CTL UNIT PER 24-28-01 SHEET 1. THIS IN TURN DETERMINED THAT THE R DISPLAY CTL UNIT (M7242) WAS NO GOOD. AFTER AGAIN CONFERRING WITH THE ACR Y MAINT CTLR; HE TOLD ME TO DEFER THE HYD MOTOR GENERATOR AS INOP PER THE MEL SINCE THIS IS WHAT WAS NOT WORKING PER THE ETOPS PREDEP CHK. AFTER TAKING A FEW DAYS OFF AND TESTING A COUPLE MORE ACFT; I FELT THIS WAS NOT PROPER. I THOUGHT THE R DISPLAY CTL UNIT SHOULD HAVE BEEN DEFERRED. AFTER MORE RESEARCH OF THE MEL; I DO NOT BELIEVE THE DISPLAY CTL UNIT CAN BE DEFERRED. THEREFORE; THE ACFT SHOULD HAVE BEEN GNDED UNTIL REPAIRED.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.