Narrative:

During descent on arrival to cvg; master caution light came on with hydraulic system light. Captain started quick reaction checklist for 'B' system failure. We continued to uneventful landing at cvg. After landing with aircraft shut down on taxiway; we discussed the events. Captain asked if during the flight I had turned off the engine #2 and #2 electric hydraulic pumps. I told him I had not. He stated that during the qrc checklist procedure he had found both pump switches in off position and had assumed I had turned them off. Previous to the master caution warning light; we had descended through a cloud layer and had turned on engine heat/anti-ice switches. These switches are identical to; and located directly above; the 'B' system hydraulic pump switches. Most likely; instead of turning engine anti-ice off; I inadvertently turned off both B system hydraulic pumps; causing the 'B' system low pressure. Supplemental information from acn 696798: I got out and complied with the loss of system 'B' non normal hydraulic checklist. When I got to system 'B' hydraulic pump switches off; I found that the pumps were already off. I assumed the copilot had turned off the pumps while I had my head down in the checklist. Evidently he had turned the pumps off by mistake instead of the engine anti-ice after coming out of IMC.

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Original NASA ASRS Text

Title: B737-800 FLT CREW HAS A 'HYD SYS B' CAUTION LIGHT; DECLARES EMER AND COMPLETES THE QRH CHKLIST.

Narrative: DURING DSCNT ON ARR TO CVG; MASTER CAUTION LIGHT CAME ON WITH HYD SYS LIGHT. CAPT STARTED QUICK REACTION CHKLIST FOR 'B' SYS FAILURE. WE CONTINUED TO UNEVENTFUL LNDG AT CVG. AFTER LNDG WITH ACFT SHUT DOWN ON TXWY; WE DISCUSSED THE EVENTS. CAPT ASKED IF DURING THE FLT I HAD TURNED OFF THE ENG #2 AND #2 ELECTRIC HYD PUMPS. I TOLD HIM I HAD NOT. HE STATED THAT DURING THE QRC CHKLIST PROC HE HAD FOUND BOTH PUMP SWITCHES IN OFF POS AND HAD ASSUMED I HAD TURNED THEM OFF. PREVIOUS TO THE MASTER CAUTION WARNING LIGHT; WE HAD DSNDED THROUGH A CLOUD LAYER AND HAD TURNED ON ENG HEAT/ANTI-ICE SWITCHES. THESE SWITCHES ARE IDENTICAL TO; AND LOCATED DIRECTLY ABOVE; THE 'B' SYS HYD PUMP SWITCHES. MOST LIKELY; INSTEAD OF TURNING ENG ANTI-ICE OFF; I INADVERTENTLY TURNED OFF BOTH B SYS HYD PUMPS; CAUSING THE 'B' SYS LOW PRESSURE. SUPPLEMENTAL INFO FROM ACN 696798: I GOT OUT AND COMPLIED WITH THE LOSS OF SYS 'B' NON NORMAL HYD CHKLIST. WHEN I GOT TO SYS 'B' HYD PUMP SWITCHES OFF; I FOUND THAT THE PUMPS WERE ALREADY OFF. I ASSUMED THE COPLT HAD TURNED OFF THE PUMPS WHILE I HAD MY HEAD DOWN IN THE CHKLIST. EVIDENTLY HE HAD TURNED THE PUMPS OFF BY MISTAKE INSTEAD OF THE ENG ANTI-ICE AFTER COMING OUT OF IMC.

Data retrieved from NASA's ASRS site as of January 2009 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.