Narrative:

Aircraft was preflight inspected per flight manual. No discrepancies were noted. All aspects of aircraft operation relative to the hydraulic systems were normal during flight and through engine shutdown. The oncoming crew found the green hydraulic system magnetic indicators in line with both engines shut down. Investigation by maintenance revealed one sensor cable cut and one disconnected, yielding the in line positions. It appears that although normal checks were run the improper indications were missed by looking at the magnetic indicator after engines were turning or looking and not seeing the in line conditions. Pressures on the green system were normal. Perhaps magnetic indicators should go amber when wiring is severed or disconnected instead of in line. Callback conversation with reporter revealed the following: confirmed that the system as designed could be a trap wherein the flight crew would not know the hydraulic valve position or could be led astray with a power loss to the indicators. Reporter would not comment on suspected cause of wires being tampered with nor did he give the airline involved. He reaffirmed that it should not be difficult to have the indicator lines go to amber color with loss of power. Amber is what the flight crew associated with a system malfunction.

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Original NASA ASRS Text

Title: SO REPORTS WHAT HE THINKS IS A DESIGN FLAW IN A HYDRAULIC PUMP VALVE POSITION INDICATOR.

Narrative: ACFT WAS PREFLT INSPECTED PER FLT MANUAL. NO DISCREPANCIES WERE NOTED. ALL ASPECTS OF ACFT OPERATION RELATIVE TO THE HYD SYSTEMS WERE NORMAL DURING FLT AND THROUGH ENG SHUTDOWN. THE ONCOMING CREW FOUND THE GREEN HYD SYS MAGNETIC INDICATORS IN LINE WITH BOTH ENGS SHUT DOWN. INVESTIGATION BY MAINT REVEALED ONE SENSOR CABLE CUT AND ONE DISCONNECTED, YIELDING THE IN LINE POSITIONS. IT APPEARS THAT ALTHOUGH NORMAL CHKS WERE RUN THE IMPROPER INDICATIONS WERE MISSED BY LOOKING AT THE MAGNETIC INDICATOR AFTER ENGS WERE TURNING OR LOOKING AND NOT SEEING THE IN LINE CONDITIONS. PRESSURES ON THE GREEN SYS WERE NORMAL. PERHAPS MAGNETIC INDICATORS SHOULD GO AMBER WHEN WIRING IS SEVERED OR DISCONNECTED INSTEAD OF IN LINE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: CONFIRMED THAT THE SYS AS DESIGNED COULD BE A TRAP WHEREIN THE FLT CREW WOULD NOT KNOW THE HYD VALVE POS OR COULD BE LED ASTRAY WITH A PWR LOSS TO THE INDICATORS. RPTR WOULD NOT COMMENT ON SUSPECTED CAUSE OF WIRES BEING TAMPERED WITH NOR DID HE GIVE THE AIRLINE INVOLVED. HE REAFFIRMED THAT IT SHOULD NOT BE DIFFICULT TO HAVE THE INDICATOR LINES GO TO AMBER COLOR WITH LOSS OF POWER. AMBER IS WHAT THE FLT CREW ASSOCIATED WITH A SYSTEM MALFUNCTION.

Data retrieved from NASA's ASRS site as of August 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.