Narrative:

During cruise the hydraulic high temperature light for the right hydraulic system was annunciated on the overhead annunciator panel (oap). Both the hydraulic transfer pump and electric auxiliary hydraulic pumps were off. The procedure in the pom for high temperature was accomplished which included turning the right engine driven hydraulic pump off. Next step was to monitor the high temperature light allowing time to extinguish. Review of the ships logbook revealed 2 prior similar instances. After 25 mins, high temperature light on the oap remained illuminated. Subsequent to radio conversation with our maintenance coordinator I noted that the right system hydraulic pressure still indicated 3000 psi even though all hydraulic pumps had been turned off. Further investigation showed that even though the right engine driven pump was being turned on and off, the pump continued to operate. I had no way of turning off the pump, and this failing pump was causing and maintaining the hydraulic high temperature light. An emergency was declared and descent from cruise altitude initiated. During the descent, the high temperature light extinguished. All hydraulic operated components worked normally during approach and landing. An uneventful landing was accomplished at cvg using the transfer hydraulic and auxiliary hydraulic pumps. The engine driven pump was in the off position, but was still operating. Callback conversation with reporter revealed the following information: new information was obtained when reporter called analyst back. Flight had been in level flight for about 15 mins after departing dfw airport when high temperature light came on. PIC and first officer performed the checklist items, then PIC called maintenance control and dispatch to advise same of situation. All concurred that, in view of the aircraft maintenance history from logbook, that the light would go out and that it would be safe for flight to operate to destination airport of cvg. No one suggested that the PIC check the hydraulic pressure gauge to see if indeed the pressure had reduced in response to hydraulic pump switch being turned off as per checklist. Captain stated that he was led down the 'primrose' path in having read the previous write-ups wherein the light did go out after switch activation. He never thought to check the pressure until about 20 mins later, and then couldn't believe the gauge, still showing 3000 pounds of pressure. He assumes that the 2 previous occasions worked for the crew, in that the pump did turn off. He further explained that the pitfall is that the warning light is on the captain's side overhead panel, and the switch/pressure gauge is by the first officer's left knee, some distance apart. To further cloud the issue, these pumps are never checked to see if they can be turned off. Captain tried to turn pump off by also pulling the control circuit breaker for it, to no avail. He cannot explain why the light went out after he declared an emergency and started down in the cvg area. No devices were used. Auxiliary pump on below 10000 ft. Post-flight inspection revealed that the wires going to the switch were cramped too tightly by either air carrier or manufacturer maintenance department, thereby actually snipping the wire and breaking it. He suggested to his air carrier that aircraft procedures in preflight should include turning off the pump and then checking pressure to see if it is turned off. This same philosophy should be incorporated in the abnormal checklist as an inordinate amount of time is wasted in waiting for the temperature light to go out after switch use, without any guarantee that it did reduce the pressure. He has had 1 more experience of an aircraft with a pump that would not turn off and will send in another report. He feels that this has the potential to be a recurring or chronic problem.

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Original NASA ASRS Text

Title: ACFT EQUIP PROBLEM MALFUNCTION MANDATES NEED FOR EMER DIVERSION TO ALT ARPT FOR LNDG.

Narrative: DURING CRUISE THE HYD HIGH TEMP LIGHT FOR THE R HYD SYS WAS ANNUNCIATED ON THE OVERHEAD ANNUNCIATOR PANEL (OAP). BOTH THE HYD TRANSFER PUMP AND ELECTRIC AUX HYD PUMPS WERE OFF. THE PROC IN THE POM FOR HIGH TEMP WAS ACCOMPLISHED WHICH INCLUDED TURNING THE R ENG DRIVEN HYD PUMP OFF. NEXT STEP WAS TO MONITOR THE HIGH TEMP LIGHT ALLOWING TIME TO EXTINGUISH. REVIEW OF THE SHIPS LOGBOOK REVEALED 2 PRIOR SIMILAR INSTANCES. AFTER 25 MINS, HIGH TEMP LIGHT ON THE OAP REMAINED ILLUMINATED. SUBSEQUENT TO RADIO CONVERSATION WITH OUR MAINT COORDINATOR I NOTED THAT THE R SYS HYD PRESSURE STILL INDICATED 3000 PSI EVEN THOUGH ALL HYD PUMPS HAD BEEN TURNED OFF. FURTHER INVESTIGATION SHOWED THAT EVEN THOUGH THE R ENG DRIVEN PUMP WAS BEING TURNED ON AND OFF, THE PUMP CONTINUED TO OPERATE. I HAD NO WAY OF TURNING OFF THE PUMP, AND THIS FAILING PUMP WAS CAUSING AND MAINTAINING THE HYD HIGH TEMP LIGHT. AN EMER WAS DECLARED AND DSCNT FROM CRUISE ALT INITIATED. DURING THE DSCNT, THE HIGH TEMP LIGHT EXTINGUISHED. ALL HYD OPERATED COMPONENTS WORKED NORMALLY DURING APCH AND LNDG. AN UNEVENTFUL LNDG WAS ACCOMPLISHED AT CVG USING THE TRANSFER HYD AND AUX HYD PUMPS. THE ENG DRIVEN PUMP WAS IN THE OFF POS, BUT WAS STILL OPERATING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: NEW INFO WAS OBTAINED WHEN RPTR CALLED ANALYST BACK. FLT HAD BEEN IN LEVEL FLT FOR ABOUT 15 MINS AFTER DEPARTING DFW ARPT WHEN HIGH TEMP LIGHT CAME ON. PIC AND FO PERFORMED THE CHKLIST ITEMS, THEN PIC CALLED MAINT CTL AND DISPATCH TO ADVISE SAME OF SITUATION. ALL CONCURRED THAT, IN VIEW OF THE ACFT MAINT HISTORY FROM LOGBOOK, THAT THE LIGHT WOULD GO OUT AND THAT IT WOULD BE SAFE FOR FLT TO OPERATE TO DEST ARPT OF CVG. NO ONE SUGGESTED THAT THE PIC CHK THE HYD PRESSURE GAUGE TO SEE IF INDEED THE PRESSURE HAD REDUCED IN RESPONSE TO HYD PUMP SWITCH BEING TURNED OFF AS PER CHKLIST. CAPT STATED THAT HE WAS LED DOWN THE 'PRIMROSE' PATH IN HAVING READ THE PREVIOUS WRITE-UPS WHEREIN THE LIGHT DID GO OUT AFTER SWITCH ACTIVATION. HE NEVER THOUGHT TO CHK THE PRESSURE UNTIL ABOUT 20 MINS LATER, AND THEN COULDN'T BELIEVE THE GAUGE, STILL SHOWING 3000 POUNDS OF PRESSURE. HE ASSUMES THAT THE 2 PREVIOUS OCCASIONS WORKED FOR THE CREW, IN THAT THE PUMP DID TURN OFF. HE FURTHER EXPLAINED THAT THE PITFALL IS THAT THE WARNING LIGHT IS ON THE CAPT'S SIDE OVERHEAD PANEL, AND THE SWITCH/PRESSURE GAUGE IS BY THE FO'S L KNEE, SOME DISTANCE APART. TO FURTHER CLOUD THE ISSUE, THESE PUMPS ARE NEVER CHKED TO SEE IF THEY CAN BE TURNED OFF. CAPT TRIED TO TURN PUMP OFF BY ALSO PULLING THE CTL CIRCUIT BREAKER FOR IT, TO NO AVAIL. HE CANNOT EXPLAIN WHY THE LIGHT WENT OUT AFTER HE DECLARED AN EMER AND STARTED DOWN IN THE CVG AREA. NO DEVICES WERE USED. AUX PUMP ON BELOW 10000 FT. POST-FLT INSPECTION REVEALED THAT THE WIRES GOING TO THE SWITCH WERE CRAMPED TOO TIGHTLY BY EITHER ACR OR MANUFACTURER MAINT DEPT, THEREBY ACTUALLY SNIPPING THE WIRE AND BREAKING IT. HE SUGGESTED TO HIS ACR THAT ACFT PROCS IN PREFLT SHOULD INCLUDE TURNING OFF THE PUMP AND THEN CHKING PRESSURE TO SEE IF IT IS TURNED OFF. THIS SAME PHILOSOPHY SHOULD BE INCORPORATED IN THE ABNORMAL CHKLIST AS AN INORDINATE AMOUNT OF TIME IS WASTED IN WAITING FOR THE TEMP LIGHT TO GO OUT AFTER SWITCH USE, WITHOUT ANY GUARANTEE THAT IT DID REDUCE THE PRESSURE. HE HAS HAD 1 MORE EXPERIENCE OF AN ACFT WITH A PUMP THAT WOULD NOT TURN OFF AND WILL SEND IN ANOTHER RPT. HE FEELS THAT THIS HAS THE POTENTIAL TO BE A RECURRING OR CHRONIC PROBLEM.

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.