Narrative:

Prior crew briefed 'a' hydraulic quantity gauge flickering, then back to normal. Flying into slc broken cloud layer into airport, reported light to moderate rime icing (confirmed, picked up moderate rime). At 10500 ft MSL, reported field in sight (at approximately 4000-6000 ft east (abeam) field. Cleared visual approach, but to remain within 12 NM of field. We needed to get down (lose altitude and configure as soon as possible -- contributing factor). I, as PNF, was accomplishing approach checklist, when captain asked to turn off anti-ice. Captain, seeing I was occupied with checklist duties, reached up to turn off the anti-ice. Unbeknownst to me, in doing so, actually turned off 'a' system hydraulics. Captain declared emergency. I, the PNF, proceeded to run loss of system 'a' hydraulics checklist. Upon reaching point in checklist to turn pumps off, I looked up and saw the pumps in the off position. Knowing that the captain knew I was very busy, I assumed he turned the switches off (contributing factor, not questioning my assumption). I also, after completing the emergency checklist and landing checklist, finally reached up to turn anti-ice off prior to land. Checklists and landing were uneventful. Discussing the situation on the ground, we discovered our mistake. Contributing factors: prebriefed hydraulic problem. Lack of communication -- both from myself (questioning assumption and captain for turning anti-ice off). Prevention of problem occurring: better communication. Any time a switch is moved, inform other person. Supplemental information from acn 428458: I knew the first officer was extremely busy and we were somewhat compressed for time. So, my first mistake was, I reached up to turn off the anti-ice to 'help' ease the first officer's workload. My second mistake, I didn't finish looking where my hand went and didn't tell the first officer. As a result, unknown to me, I turned off our 'a' system hydraulic pumps. Being in a high workload turn to final, I had just helped create our emergency, with resulting master caution and hydraulic lights coming on. We landed uneventfully. After landing, we discussed what had happened (we were stopped on taxiway). It was then I realized my error. We turned the 'a' pumps back on and all system were normal. Another piece of this picture that caused us to affirm hydraulic failure was a previous write-up of a hydraulic quantity gauge malfunction. It was actually working fine, but because of my error, we thought it may have been reading wrong due to zero 'a' pressure (the write-up had been cleared). My logbook write-up reflected my error in turning off 2 good 'a' pumps to prevent any unnecessary maintenance. I also spoke with our operations director within 2 hours of incident and gave him a full verbal account of what happened.

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Original NASA ASRS Text

Title: A BUSY FLC IN A TWIN ENG ACR STARTS TO PERFORM THEIR DUTIES OUT OF SEQUENCE. THE CAPT TURNED OFF THE 'A' HYD SYS INSTEAD OF THE ANTI-ICE SYS AND THEY ASSUME THAT THE 'A' SYS HAD FAILED AND THEY ACT ACCORDINGLY.

Narrative: PRIOR CREW BRIEFED 'A' HYD QUANTITY GAUGE FLICKERING, THEN BACK TO NORMAL. FLYING INTO SLC BROKEN CLOUD LAYER INTO ARPT, RPTED LIGHT TO MODERATE RIME ICING (CONFIRMED, PICKED UP MODERATE RIME). AT 10500 FT MSL, RPTED FIELD IN SIGHT (AT APPROX 4000-6000 FT E (ABEAM) FIELD. CLRED VISUAL APCH, BUT TO REMAIN WITHIN 12 NM OF FIELD. WE NEEDED TO GET DOWN (LOSE ALT AND CONFIGURE ASAP -- CONTRIBUTING FACTOR). I, AS PNF, WAS ACCOMPLISHING APCH CHKLIST, WHEN CAPT ASKED TO TURN OFF ANTI-ICE. CAPT, SEEING I WAS OCCUPIED WITH CHKLIST DUTIES, REACHED UP TO TURN OFF THE ANTI-ICE. UNBEKNOWNST TO ME, IN DOING SO, ACTUALLY TURNED OFF 'A' SYS HYDS. CAPT DECLARED EMER. I, THE PNF, PROCEEDED TO RUN LOSS OF SYS 'A' HYDS CHKLIST. UPON REACHING POINT IN CHKLIST TO TURN PUMPS OFF, I LOOKED UP AND SAW THE PUMPS IN THE OFF POS. KNOWING THAT THE CAPT KNEW I WAS VERY BUSY, I ASSUMED HE TURNED THE SWITCHES OFF (CONTRIBUTING FACTOR, NOT QUESTIONING MY ASSUMPTION). I ALSO, AFTER COMPLETING THE EMER CHKLIST AND LNDG CHKLIST, FINALLY REACHED UP TO TURN ANTI-ICE OFF PRIOR TO LAND. CHKLISTS AND LNDG WERE UNEVENTFUL. DISCUSSING THE SIT ON THE GND, WE DISCOVERED OUR MISTAKE. CONTRIBUTING FACTORS: PREBRIEFED HYD PROB. LACK OF COM -- BOTH FROM MYSELF (QUESTIONING ASSUMPTION AND CAPT FOR TURNING ANTI-ICE OFF). PREVENTION OF PROB OCCURRING: BETTER COM. ANY TIME A SWITCH IS MOVED, INFORM OTHER PERSON. SUPPLEMENTAL INFO FROM ACN 428458: I KNEW THE FO WAS EXTREMELY BUSY AND WE WERE SOMEWHAT COMPRESSED FOR TIME. SO, MY FIRST MISTAKE WAS, I REACHED UP TO TURN OFF THE ANTI-ICE TO 'HELP' EASE THE FO'S WORKLOAD. MY SECOND MISTAKE, I DIDN'T FINISH LOOKING WHERE MY HAND WENT AND DIDN'T TELL THE FO. AS A RESULT, UNKNOWN TO ME, I TURNED OFF OUR 'A' SYS HYD PUMPS. BEING IN A HIGH WORKLOAD TURN TO FINAL, I HAD JUST HELPED CREATE OUR EMER, WITH RESULTING MASTER CAUTION AND HYD LIGHTS COMING ON. WE LANDED UNEVENTFULLY. AFTER LNDG, WE DISCUSSED WHAT HAD HAPPENED (WE WERE STOPPED ON TXWY). IT WAS THEN I REALIZED MY ERROR. WE TURNED THE 'A' PUMPS BACK ON AND ALL SYS WERE NORMAL. ANOTHER PIECE OF THIS PICTURE THAT CAUSED US TO AFFIRM HYD FAILURE WAS A PREVIOUS WRITE-UP OF A HYD QUANTITY GAUGE MALFUNCTION. IT WAS ACTUALLY WORKING FINE, BUT BECAUSE OF MY ERROR, WE THOUGHT IT MAY HAVE BEEN READING WRONG DUE TO ZERO 'A' PRESSURE (THE WRITE-UP HAD BEEN CLRED). MY LOGBOOK WRITE-UP REFLECTED MY ERROR IN TURNING OFF 2 GOOD 'A' PUMPS TO PREVENT ANY UNNECESSARY MAINT. I ALSO SPOKE WITH OUR OPS DIRECTOR WITHIN 2 HRS OF INCIDENT AND GAVE HIM A FULL VERBAL ACCOUNT OF WHAT HAPPENED.

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.