Narrative:

During descent checks, when I turned the right engine driven hydraulic pump switch to high, the pressure immediately dropped to zero and the corresponding quantity gauge snapped to the highest reading, above 19 quarts. The left engine pump had already been switched to high normally and neither the standby nor xfer pumps had been switched on yet. I (first officer) was flying and kept the controls while the captain got out the emergency checklist. He informed ATC that we had a hydraulic problem and advised them we would give more information after we ran our checklists. We did not declare an emergency at this point. The captain started with the 'left or right hydraulic pressure low light' checklist. When he got to the note 'an off scale high quantity indication may be observed when a hydraulic system is depressurized,' we both interpreted this to mean that the high quantity reading on the right hydraulic gauge was erroneous due to a total loss of fluid in that system. This led to answering the next box on the checklist: is quantity low -- decreasing or zero? As a yes and proceeding to the 'left or right hydraulic quantity zero, low or decreasing,' after completing that checklist, he declared an emergency with ATC requesting an approach to the long runway 27L and turned over the radios to me while he coordinated with the flight attendants and made a PA. I had approach extend us on downwind to get time to complete all checklists and brief the approach. We did the emergency gear extension per the checklist and started the approach. Due to the crosswind limit being excessive for runway 27L, we changed to a localizer runway 30 approach and landed uneventfully. When maintenance was preparing to tow us, they had us turn on the auxiliary hydraulic pump to try to raise the gear doors. At that time, we discovered that there was still fluid in the system. While running the emergency checklists, we had not tried to turn on the auxiliary pump because the checklist he was using did not call for it and we did not want to run what we thought was a dry pump, thinking that it could be a possible fire risk. In hindsight after rereading every possible option on the first checklist, 'left or right hydraulic pressurization low light,' we realized that continuing that checklist after answering the first decision as a 'no,' would have eventually lead to turning the auxiliary pump on and possibly having normal hydraulic pressure available to lower the landing gear normally and have normal rudder power available. Supplemental information from acn 604713: I informed the passenger of the malfunction emphasizing the aircraft was fine, that there was a possibility of observing sparks, that we would be stopping on the runway, that, as a precaution, they would see many emergency vehicles, that the gear would be pinned and the aircraft would be towed to the gate. Finished with checklists and checked with the flight attendants to ensure all was stowed. Afterwards, I discussed the event with the first officer, what we had learned and I began to feel that we had not lost all fluid. It was my real time perception/evaluation that we had. I feel very strongly that the note concerning the 'off the scale indication' led me to that evaluation, and that it needs to be reworded and relocated.

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Original NASA ASRS Text

Title: MD80 CREW HAD THE R ENG DRIVEN HYD PUMP FAIL ON APCH TO MIA.

Narrative: DURING DSCNT CHKS, WHEN I TURNED THE R ENG DRIVEN HYD PUMP SWITCH TO HIGH, THE PRESSURE IMMEDIATELY DROPPED TO ZERO AND THE CORRESPONDING QUANTITY GAUGE SNAPPED TO THE HIGHEST READING, ABOVE 19 QUARTS. THE L ENG PUMP HAD ALREADY BEEN SWITCHED TO HIGH NORMALLY AND NEITHER THE STANDBY NOR XFER PUMPS HAD BEEN SWITCHED ON YET. I (FO) WAS FLYING AND KEPT THE CTLS WHILE THE CAPT GOT OUT THE EMER CHKLIST. HE INFORMED ATC THAT WE HAD A HYD PROB AND ADVISED THEM WE WOULD GIVE MORE INFO AFTER WE RAN OUR CHKLISTS. WE DID NOT DECLARE AN EMER AT THIS POINT. THE CAPT STARTED WITH THE 'L OR R HYD PRESSURE LOW LIGHT' CHKLIST. WHEN HE GOT TO THE NOTE 'AN OFF SCALE HIGH QUANTITY INDICATION MAY BE OBSERVED WHEN A HYD SYS IS DEPRESSURIZED,' WE BOTH INTERPRETED THIS TO MEAN THAT THE HIGH QUANTITY READING ON THE R HYD GAUGE WAS ERRONEOUS DUE TO A TOTAL LOSS OF FLUID IN THAT SYS. THIS LED TO ANSWERING THE NEXT BOX ON THE CHKLIST: IS QUANTITY LOW -- DECREASING OR ZERO? AS A YES AND PROCEEDING TO THE 'L OR R HYD QUANTITY ZERO, LOW OR DECREASING,' AFTER COMPLETING THAT CHKLIST, HE DECLARED AN EMER WITH ATC REQUESTING AN APCH TO THE LONG RWY 27L AND TURNED OVER THE RADIOS TO ME WHILE HE COORDINATED WITH THE FLT ATTENDANTS AND MADE A PA. I HAD APCH EXTEND US ON DOWNWIND TO GET TIME TO COMPLETE ALL CHKLISTS AND BRIEF THE APCH. WE DID THE EMER GEAR EXTENSION PER THE CHKLIST AND STARTED THE APCH. DUE TO THE XWIND LIMIT BEING EXCESSIVE FOR RWY 27L, WE CHANGED TO A LOC RWY 30 APCH AND LANDED UNEVENTFULLY. WHEN MAINT WAS PREPARING TO TOW US, THEY HAD US TURN ON THE AUX HYD PUMP TO TRY TO RAISE THE GEAR DOORS. AT THAT TIME, WE DISCOVERED THAT THERE WAS STILL FLUID IN THE SYS. WHILE RUNNING THE EMER CHKLISTS, WE HAD NOT TRIED TO TURN ON THE AUX PUMP BECAUSE THE CHKLIST HE WAS USING DID NOT CALL FOR IT AND WE DID NOT WANT TO RUN WHAT WE THOUGHT WAS A DRY PUMP, THINKING THAT IT COULD BE A POSSIBLE FIRE RISK. IN HINDSIGHT AFTER REREADING EVERY POSSIBLE OPTION ON THE FIRST CHKLIST, 'L OR R HYD PRESSURIZATION LOW LIGHT,' WE REALIZED THAT CONTINUING THAT CHKLIST AFTER ANSWERING THE FIRST DECISION AS A 'NO,' WOULD HAVE EVENTUALLY LEAD TO TURNING THE AUX PUMP ON AND POSSIBLY HAVING NORMAL HYD PRESSURE AVAILABLE TO LOWER THE LNDG GEAR NORMALLY AND HAVE NORMAL RUDDER PWR AVAILABLE. SUPPLEMENTAL INFO FROM ACN 604713: I INFORMED THE PAX OF THE MALFUNCTION EMPHASIZING THE ACFT WAS FINE, THAT THERE WAS A POSSIBILITY OF OBSERVING SPARKS, THAT WE WOULD BE STOPPING ON THE RWY, THAT, AS A PRECAUTION, THEY WOULD SEE MANY EMER VEHICLES, THAT THE GEAR WOULD BE PINNED AND THE ACFT WOULD BE TOWED TO THE GATE. FINISHED WITH CHKLISTS AND CHKED WITH THE FLT ATTENDANTS TO ENSURE ALL WAS STOWED. AFTERWARDS, I DISCUSSED THE EVENT WITH THE FO, WHAT WE HAD LEARNED AND I BEGAN TO FEEL THAT WE HAD NOT LOST ALL FLUID. IT WAS MY REAL TIME PERCEPTION/EVALUATION THAT WE HAD. I FEEL VERY STRONGLY THAT THE NOTE CONCERNING THE 'OFF THE SCALE INDICATION' LED ME TO THAT EVALUATION, AND THAT IT NEEDS TO BE REWORDED AND RELOCATED.

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.