B737-800
Flight Crew Air Transport Pilot (ATP)
Time Pressure; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach
Human Factors
I'm fairly new to the 737 and this was my first leg after being off for several weeks due to surgery and recuperation. I was the pilot flying from ORD at FL280. Enroute we entered some clouds so I turned on the engine A/I (Anti-ice). During descent we exited the clouds so I reached up and turned off the engine A/I. A little while later the yaw damper light illuminated. We followed the QRH procedure but the light remained on. With our current weather conditions this was not an issue according to the QRH. We flew the WATSN TWO arrival; switched over to approach control; and were cleared for the runway 28C ILS. Approach asked us to slow to 210kts. I selected flaps 1 then 5. Because we were over taking an aircraft ahead of us; we were further asked to slow to 180kts. I then selected flaps 10 but was having a hard time slowing. Approach then asked us to slow to 170kts. About this time; while in speed intervention; I noticed an A in the speed window. I went gear down then flaps 15 and 25 but was still having difficulty slowing down. Next I noticed that I was approaching a red zipper at the bottom of the speed tape! The First Officer and I briefly discussed that something was not right and that we needed to go-around and sort it out. Approach control beat us to the punch due to traffic spacing and climbed us to 5;000 feet at 210kts. While executing the go-around; we noticed that the flap indicator was in the up position (i.e. not in agreement with the flap handle). But which was correct-- the flap indicator or the flap handle? I decided that it was the flap indicator because of the airspeed alerts that I had been getting (i.e. I was choosing to believe the AOA). But what was causing this? I first made sure that all the CBs were in; they were. Next I thought hydraulics. A quick scan of the hydraulic systems showed that both pumps of the B system hydraulics (electric and engine) were in the off position!  Apparently I had inadvertently turned off the B system pumps when I thought I was turning off the engine A/I. Once the pumps were turned back on everything operated normally; including the yaw damper. We were vectored back to runway 28C and made an uneventful approach and landing. Lessons learned: 1. Make sure to move the correct switch when moving a switch.  2. Make sure to check flap position indicator when moving the flap handle.  3. If things don't seem right they probably aren't. Buy yourself some time and figure it out. In this case go-around which we did.  4. If you have to trust something regarding the flyability of the aircraft; the AOA is a good place to start.
[Report narrative contained no additional information].
Captain of a B737-800 accidentally turns off the Hydraulic 'B' pumps vice the Engine anti-ice which he was reaching for. Shortly after; the Yaw damper light turns on and the crew notices the aircraft not slowing as expected. Noticing something isn't right they announce a go-around to work the problem and realize the Captain's mistake. Switches are corrected and warning lights turn off and flaps are retracted on schedule. Landing follows shortly after.