Narrative:

On climb out at about 17000 feet; there was a cloud layer so I told first officer 'heaters are coming on' and I turned both start switches to continuous and both engine anti ice switches on. At about FL180 we came out of cloud layer and I told first officer 'heaters coming off' and I thought I turned off both engine anti ice switches and I turned off both start switches (there was a pretty good glare from the sun after we came out of clouds). What I actually did was turn off both electric and engine driven hydraulic B pumps. At about FL230 we got a master caution light with flight control light. I looked above my head and saw the system B low reservoir light (I did not see the B electric and engine driven hydraulic switch low-pressure lights (it may have been the glare of the sun). I pulled up the hydraulic page on lower icas and saw that the B hydraulic system was about 400 psi. Before my first officer could verify anything; I pointed to the system B low reservoir light and then to the lower EICAS (I affectively drew his eyes away from doing his own verification of the master caution light). Then I told first officer to ask ATC if we could level off at FL250 to work a problem.I told first officer I had radios and for him to run the QRH for loss of hydraulic system B. While first officer was running the QRH; I told ATC we were gonna go back and would like vectors to stay in the area while we were running some checklists. I sent a quick ACARS note to dispatch and told flight attendants and passengers we were going back. First officer thought I had turned hydraulic switches off; like the checklist calls for. Got a descent down to 10;000 feet and were getting vectors for a 20 mile final. Somewhere in the descent I looked up and saw the blue lights of the engine anti ice and realized that I had turned off the B hydraulic pump switches and caused this whole mess. I pointed this out to the first officer and we put all switches to correct setting. [We] cancelled with ATC and I decided to continue to the departure field for fuel consideration (calculated we would get to destination with only about 4000lbs of fuel). Landed uneventfully and parked to gate. I called dispatch to fill him in on my error. We got another aircraft and went to destination.

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Original NASA ASRS Text

Title: B737 flight crew reported inadvertently turning off the hydraulic system while in flight.

Narrative: On climb out at about 17000 feet; there was a cloud layer so I told first officer 'heaters are coming on' and I turned both start switches to continuous and both engine anti ice switches on. At about FL180 we came out of cloud layer and I told first officer 'heaters coming off' and I thought I turned off both engine anti ice switches and I turned off both start switches (there was a pretty good glare from the sun after we came out of clouds). What I actually did was turn off both electric and engine driven hydraulic B pumps. At about FL230 we got a Master Caution light with Flight Control light. I looked above my head and saw the system B low reservoir light (I did not see the B electric and engine driven hydraulic switch low-pressure lights (it may have been the glare of the sun). I pulled up the hydraulic page on lower ICAS and saw that the B hydraulic system was about 400 PSI. Before my first officer could verify anything; I pointed to the system B low reservoir light and then to the lower EICAS (I affectively drew his eyes away from doing his own verification of the master caution light). Then I told first officer to ask ATC if we could level off at FL250 to work a problem.I told first officer I had radios and for him to run the QRH for loss of hydraulic system B. While first officer was running the QRH; I told ATC we were gonna go back and would like vectors to stay in the area while we were running some checklists. I sent a quick ACARS note to dispatch and told flight attendants and passengers we were going back. First officer thought I had turned hydraulic switches off; like the checklist calls for. Got a descent down to 10;000 feet and were getting vectors for a 20 mile final. Somewhere in the descent I looked up and saw the blue lights of the engine anti ice and realized that I had turned off the B hydraulic pump switches and caused this whole mess. I pointed this out to the first officer and we put all switches to correct setting. [We] cancelled with ATC and I decided to continue to the departure field for fuel consideration (calculated we would get to destination with only about 4000lbs of fuel). Landed uneventfully and parked to gate. I called dispatch to fill him in on my error. We got another aircraft and went to destination.

Data retrieved from NASA's ASRS site 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.