B737 first officer attributed captain's improper positioning of the fuel pump and crossfeed switches...

Narrative:

While at cruise flight; I noticed the autopilot kept increasing aileron trim. I mentioned it to my captain and he immediately realized we had a 4;000 pound fuel imbalance. All four main tank fuel pump switches were in the 'on' position with the crossfeed valve in the open position. He promptly began balancing fuel. By the time we landed the fuel was balanced. We believe my captain may have opened the crossfeed valve when he turned off the center tank pumps.I think there were many factors that contributed to this occurrence. Neither one of us flies the classic frequently. Therefore; there is a lack of familiarity with the aircraft. The fuel gauges are closer to the captain and were not in my scan. The captain experienced interference from the newer model fuel procedure and out of habit moved the crossfeed valve after turning off the center tank pumps. Also; if the system is functioning correctly; I believe the fuel system should have remained reasonably balanced. From the crew perspective; making sure to occasionally scan the fuel gauges and both crew members verifying each other's switch movements would have helped prevent this situation. From a procedure perspective; having like aircraft with different procedures opens the door to these mistakes. Also; flying another aircraft infrequently makes it difficult to include different gauges in your scan.

Original NASA ASRS Text

Title: B737 First Officer attributed Captain's improper positioning of the fuel pump and crossfeed switches to differences in B737 models flown by the company and to the fact that the Captain and the First Officer usually flew the newer models.

Narrative: While at cruise flight; I noticed the autopilot kept increasing aileron trim. I mentioned it to my Captain and he immediately realized we had a 4;000 pound fuel imbalance. All four main tank fuel pump switches were in the 'On' position with the crossfeed valve in the open position. He promptly began balancing fuel. By the time we landed the fuel was balanced. We believe my Captain may have opened the crossfeed valve when he turned off the center tank pumps.I think there were many factors that contributed to this occurrence. Neither one of us flies the classic frequently. Therefore; there is a lack of familiarity with the aircraft. The fuel gauges are closer to the Captain and were not in my scan. The Captain experienced interference from the newer model fuel procedure and out of habit moved the crossfeed valve after turning off the center tank pumps. Also; if the system is functioning correctly; I believe the fuel system should have remained reasonably balanced. From the crew perspective; making sure to occasionally scan the fuel gauges and both crew members verifying each other's switch movements would have helped prevent this situation. From a procedure perspective; having like aircraft with different procedures opens the door to these mistakes. Also; flying another aircraft infrequently makes it difficult to include different gauges in your scan.

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.

Attributes
ACN	1295674
Time
Date	201509
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise Initial Approach
Flight Plan	IFR
Component
Aircraft Component	Fuel Crossfeed
Person 1
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 188
Events
Anomaly	Deviation - Procedural Published Material / Policy Inflight Event / Encounter Fuel Issue

B737 first officer attributed captain's improper positioning of the fuel pump and crossfeed switches to differences in B737 models flown by the company and to the fact that the captain and the first officer usually flew the newer models.