Narrative:

While taxiing to the gate at dfw all hydraulic fluid was lost from the left system and hydraulic pressure went to '0' in both system. Hydraulic pressure to the right system was restored to normal after the xfer pump was turned off. One of the highlights of revision #112 to the S80 operating manual stated that loss of fluid in 1 hydraulic system could result in loss of pressure in both system if the low level switch failed to turn off the xfer pump. I assumed that this information was given to us because this type of situation was possible, but not very likely. My first officer, however, was not at all surprised that the loss of fluid in 1 system caused pressure to be lost in both system. He has now lost all fluid in 1 system twice and in both instances pressure in both system has gone to '0.' callback conversation with reporter revealed the following information: this reporter had just landed and turned off of the runway when he realized that he had no steering control to continue his turn onto the taxiway toward the gate area so he stopped the aircraft. He and the first officer checked the hydraulic system and that is when they saw that the left system had no fluid and the right had no pressure. The first officer then turned off the xfer pump and the right system pressure was restored. The cause of the loss was a leak in the left reverser and normally a fluid loss in either system would signal the xfer pump to go off. For some reason, unknown to the reporter, this part of the hydraulic protection system did not work. When the xfer pump does not go off in this situation the remaining hydraulic system pressure goes to '0.' the reporter said that he recalled this phenomenon once the first officer started to discuss his prior experience with it.

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Original NASA ASRS Text

Title: AN ACR MD80, SUPER 80 FLC LOST THE FLUID IN THE L HYD SYS AFTER LNDG AND THE R HYD SYS PRESSURE WENT TO '0.' THE FLC STOPPED THE ACFT ON THE TXWY USING BRAKE ACCUMULATOR PRESSURE.

Narrative: WHILE TAXIING TO THE GATE AT DFW ALL HYD FLUID WAS LOST FROM THE L SYS AND HYD PRESSURE WENT TO '0' IN BOTH SYS. HYD PRESSURE TO THE R SYS WAS RESTORED TO NORMAL AFTER THE XFER PUMP WAS TURNED OFF. ONE OF THE HIGHLIGHTS OF REVISION #112 TO THE S80 OPERATING MANUAL STATED THAT LOSS OF FLUID IN 1 HYD SYS COULD RESULT IN LOSS OF PRESSURE IN BOTH SYS IF THE LOW LEVEL SWITCH FAILED TO TURN OFF THE XFER PUMP. I ASSUMED THAT THIS INFO WAS GIVEN TO US BECAUSE THIS TYPE OF SIT WAS POSSIBLE, BUT NOT VERY LIKELY. MY FO, HOWEVER, WAS NOT AT ALL SURPRISED THAT THE LOSS OF FLUID IN 1 SYS CAUSED PRESSURE TO BE LOST IN BOTH SYS. HE HAS NOW LOST ALL FLUID IN 1 SYS TWICE AND IN BOTH INSTANCES PRESSURE IN BOTH SYS HAS GONE TO '0.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR HAD JUST LANDED AND TURNED OFF OF THE RWY WHEN HE REALIZED THAT HE HAD NO STEERING CTL TO CONTINUE HIS TURN ONTO THE TXWY TOWARD THE GATE AREA SO HE STOPPED THE ACFT. HE AND THE FO CHKED THE HYD SYS AND THAT IS WHEN THEY SAW THAT THE L SYS HAD NO FLUID AND THE R HAD NO PRESSURE. THE FO THEN TURNED OFF THE XFER PUMP AND THE R SYS PRESSURE WAS RESTORED. THE CAUSE OF THE LOSS WAS A LEAK IN THE L REVERSER AND NORMALLY A FLUID LOSS IN EITHER SYS WOULD SIGNAL THE XFER PUMP TO GO OFF. FOR SOME REASON, UNKNOWN TO THE RPTR, THIS PART OF THE HYD PROTECTION SYS DID NOT WORK. WHEN THE XFER PUMP DOES NOT GO OFF IN THIS SIT THE REMAINING HYD SYS PRESSURE GOES TO '0.' THE RPTR SAID THAT HE RECALLED THIS PHENOMENON ONCE THE FO STARTED TO DISCUSS HIS PRIOR EXPERIENCE WITH IT.

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.