Date: 201410
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ; Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Fuel Booster Pump
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Time Pressure
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; General Declared Emergency
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: I am the Captain and was the pilot monitoring for the flight. We were delayed about 2 hours due to late arriving aircraft. There was some sense of time pressure; which was self-imposed; to get the flight out. I was dealing with a maintenance issue and requirements to contact dispatch. During the before engine start checklist I only turned on one center tank pump with fuel in the center tank. The pump I turned on was the left one. Due to aircraft design there are no pressure lights when one center pump is on and one is left off. After takeoff and during the 10000 foot check on the after takeoff climb check I noticed that the right main tank fuel was decreasing when fuel feed should have been from the center. I was flying away from Airport ZZZ and going towards the mountains. As we continued to climb the right main continued to decrease. I looked at the fuel panel and did not see any lights. I got concerned that we were going away from Airport ZZZ and towards the mountain and appeared to have a fuel leak. I wanted to stay closer to Airport ZZZ while I tried to figure out the problem so I declared an emergency and asked for a turn back towards Airport ZZZ. While in the turn I noticed that the right center fuel pump was off. I turned it on and this resolved the abnormal fuel feed situation. I told departure that I was terminating the emergency and wanted to turn back on course. We basically did a 360 turn and then continued. Fuel feed was normal from this point on. We landed with normal burn. I did not feel like we were overly rushing to get out of Airport ZZZ but I obviously missed the center fuel pump during the before start engine checklist. I tend to do a scan of the overhead panel just prior to takeoff but it is more of a light check than a switch check. I will modify my scan to include switch positions. When I first noticed the imbalance I was torn between giving some time and continuing on to trouble shoot and staying close to Airport ZZZ. The imbalance was occurring rapidly so prior to doing any abnormal checklist I decided to turn back towards Airport ZZZ instead of going over the mountains. Once again I am sure I looked at the fuel panel but most likely only for lights and not switch positions. During the turn I finally noticed the switch. Two major lessons:1. Never rush (sometimes difficult to due)2. When faced with an abnormal try to wind the clock for a second and think about the most likely causes of the problem.


Second narrative: I was the flying pilot of record. On climb out; passing approximately FL180 the Captain noticed an impending fuel imbalance. Thinking we had a fuel leak; and heading away from Airport ZZZ; he quickly declared an Emergency and requested a return to Airport ZZZ. He directed me to take the radios and to continue flying the jet. We turned back toward Airport ZZZ. Descending thru 16;500 feet as the Captain started to pull out the QRH; he corrected the problem. He discovered a center boost pump was in the off position. When placed to on the fuel issue was resolved. We did not deviate from any clearance and determined we could continue. The captain undeclared the Emergency.The flight was delayed due to the aircraft needing maintenance. We departed approximately 2 hours late. All procedures appeared to be handled normally. Upon concluding the emergency we realized we missed the second center tank boost pump in the off position. We read the checklist and still did not catch our error. Looking over from my seat this boost pump switch is almost in line with the electrical generator switch. I looked over and mistook the one for the other. This drives the point home to look at what you see and need to see. I now will make sure to lean over to make sure I'm looking at the correct switch. We discussed this during the flight. We both agreed we didn't feel we rushed and yet still missed the switch. We reviewed the fuel system and associated lights.


Synopsis: While preparing for the before start checklist; a B737 Captain reports only turning on one center tank fuel pump. This is not detected by either pilot during the checklist and the flight departs in that condition. An impending fuel imbalance is detected during climb and several minutes pass before the cause is detected and corrected.