Narrative:

We were en route san to ZZZ when left hydraulic system indicator started to vibrate then decrease to less than 6 gallons. Captain called ZZZ1 maintenance for advice and was told that during approach, xfer pump should be turned on. However, we should turn it off if left quantity decreased further. During approach, flight attendants complained of fumes. Captain requested arff trucks to meet aircraft as precaution. Captain made PA to passenger telling them trucks were only a precaution. On downwind, as xfer pump was turned on as per company's previous instructions, both left and right hydraulic system pressure low lights illuminated and stayed on steady. Left quantity had dropped, right remained steady at 13. Flaps could not be extended with this lack of hydraulic pressure. Captain told me to turn off xfer pump. As xfer pump was turned off, right system pressure was recovered. We extended gear and flaps and made a normal landing. This could have become a nasty situation if the captain didn't have the vision of forethought to assess and plan out our course of action. It seems that all pressure was lost due to seizure of xfer pump. Callback conversation with reporter revealed the following information: the reporter stated that after a later review, the procedures manual did deal with the situation encountered and did not require use of the power xfer unit. The reporter said with the power xfer unit operating, the right hydraulic system dropped to trigger the low pressure warning light. The reporter stated the captain used the idea that when something is turned on and the effect is negative, then turn it off. The reporter said this was done and right system pressure recovered.

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Original NASA ASRS Text

Title: AN MD80 IN CRUISE AT FL330 HAD L HYD SYS PRESSURE AND QUANTITY DECREASE. MAINT ADVISED USE OF THE XFER PUMP. WHEN ON, R SYS PRESSURE WAS LOST.

Narrative: WE WERE ENRTE SAN TO ZZZ WHEN L HYD SYS INDICATOR STARTED TO VIBRATE THEN DECREASE TO LESS THAN 6 GALLONS. CAPT CALLED ZZZ1 MAINT FOR ADVICE AND WAS TOLD THAT DURING APCH, XFER PUMP SHOULD BE TURNED ON. HOWEVER, WE SHOULD TURN IT OFF IF L QUANTITY DECREASED FURTHER. DURING APCH, FLT ATTENDANTS COMPLAINED OF FUMES. CAPT REQUESTED ARFF TRUCKS TO MEET ACFT AS PRECAUTION. CAPT MADE PA TO PAX TELLING THEM TRUCKS WERE ONLY A PRECAUTION. ON DOWNWIND, AS XFER PUMP WAS TURNED ON AS PER COMPANY'S PREVIOUS INSTRUCTIONS, BOTH L AND R HYD SYS PRESSURE LOW LIGHTS ILLUMINATED AND STAYED ON STEADY. L QUANTITY HAD DROPPED, R REMAINED STEADY AT 13. FLAPS COULD NOT BE EXTENDED WITH THIS LACK OF HYD PRESSURE. CAPT TOLD ME TO TURN OFF XFER PUMP. AS XFER PUMP WAS TURNED OFF, R SYS PRESSURE WAS RECOVERED. WE EXTENDED GEAR AND FLAPS AND MADE A NORMAL LNDG. THIS COULD HAVE BECOME A NASTY SIT IF THE CAPT DIDN'T HAVE THE VISION OF FORETHOUGHT TO ASSESS AND PLAN OUT OUR COURSE OF ACTION. IT SEEMS THAT ALL PRESSURE WAS LOST DUE TO SEIZURE OF XFER PUMP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT AFTER A LATER REVIEW, THE PROCS MANUAL DID DEAL WITH THE SIT ENCOUNTERED AND DID NOT REQUIRE USE OF THE PWR XFER UNIT. THE RPTR SAID WITH THE PWR XFER UNIT OPERATING, THE R HYD SYS DROPPED TO TRIGGER THE LOW PRESSURE WARNING LIGHT. THE RPTR STATED THE CAPT USED THE IDEA THAT WHEN SOMETHING IS TURNED ON AND THE EFFECT IS NEGATIVE, THEN TURN IT OFF. THE RPTR SAID THIS WAS DONE AND R SYS PRESSURE RECOVERED.

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.