Narrative:

During preflight checks for flight xyz (nov/wed/00 ZZZ), the crew notified maintenance that all the cabin signs, PA system, along with all the call chimes were inoperative. After extensive troubleshooting, and several parts being replaced, the condition noted still existed. It was discovered during troubleshooting that the condition noted only occurred with external power, or APU power supplying the aircraft. There was no way to defer the system involved per the MEL with the noted system inoperative. I contacted the system engineer, xa wwz, in XXX, to see if he had ever heard, or had any ideas what was causing this problem. It was later discovered with the engines providing the ship's power, all noted system operated normally, and continued to operate normally after shutdown at the gate. On arrival, after external power was hooked up, the same noted condition existed. The in-flight crew was concerned that the noted condition had reoccurred, and thought it posed a safety problem, had they needed any of those system once the aircraft was on ground power at the gate.

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Original NASA ASRS Text

Title: A B747-400 WAS DISPATCHED IN NON-COMPLIANCE WITH THE PA, CHIME, AND PAX SIGNS DEFERRED AS INOP ON GND AND AUX PWR OK ON ENG PWR.

Narrative: DURING PREFLT CHKS FOR FLT XYZ (NOV/WED/00 ZZZ), THE CREW NOTIFIED MAINT THAT ALL THE CABIN SIGNS, PA SYS, ALONG WITH ALL THE CALL CHIMES WERE INOP. AFTER EXTENSIVE TROUBLESHOOTING, AND SEVERAL PARTS BEING REPLACED, THE CONDITION NOTED STILL EXISTED. IT WAS DISCOVERED DURING TROUBLESHOOTING THAT THE CONDITION NOTED ONLY OCCURRED WITH EXTERNAL PWR, OR APU PWR SUPPLYING THE ACFT. THERE WAS NO WAY TO DEFER THE SYS INVOLVED PER THE MEL WITH THE NOTED SYS INOP. I CONTACTED THE SYS ENGINEER, XA WWZ, IN XXX, TO SEE IF HE HAD EVER HEARD, OR HAD ANY IDEAS WHAT WAS CAUSING THIS PROB. IT WAS LATER DISCOVERED WITH THE ENGS PROVIDING THE SHIP'S PWR, ALL NOTED SYS OPERATED NORMALLY, AND CONTINUED TO OPERATE NORMALLY AFTER SHUTDOWN AT THE GATE. ON ARR, AFTER EXTERNAL PWR WAS HOOKED UP, THE SAME NOTED CONDITION EXISTED. THE INFLT CREW WAS CONCERNED THAT THE NOTED CONDITION HAD REOCCURRED, AND THOUGHT IT POSED A SAFETY PROB, HAD THEY NEEDED ANY OF THOSE SYS ONCE THE ACFT WAS ON GND PWR AT THE GATE.

Data retrieved from NASA's ASRS site as of July 2007 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.