Date: 202005
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: B757-200
Operator: Air Carrier
Flight plan: IFR
Flight phase: Final Approach
Airspace: Class B ZZZ
Aircraft component: Fuel Crossfeed
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Training / Qualification; Situational Awareness; Confusion
Second reporter function: Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: When the First Officer and I board the aircraft in ZZZ; the fuel cross valve was in the open position. Neither the FO (First Officer) or myself noticed this. We departed on schedule for our leg to ZZZ1; with the cross feed still open. The fuel config enunciation illuminated several times; AND we glanced at the fuel panel but again; I did not see the x feed valve position. As the FO called for flaps 25 on approach to ZZZ1; I noticed my yoke was highly biased toward a left wing down command. I finally saw the fuel imbalance at that time; and noticed the crossfeed open. By then; we were approximately 1;000 ft. AGL and deemed it not advisable to be changing fuel switch positions at that time. The left wing indicated 2200 pounds; the right 11;600 pounds. At 500 ft. AGL; the LOW FUEL initiation illuminated. After shut down at the gateway; we discussed how such an event could possibly HAVE happened; and what we would do to preclude such an event in the future. Each time the fuel config light illuminated; I glanced up at the fuel panel. But I believe expectation bias took over; and I never noticed the fuel imbalance itself and the crossfeed valve open. I realize the dire consequences of not being vigilant in the situation; and I take full responsibility. In the future; when I observe a fuel config light; I will not simply 'look at the fuel panel;' but will analyze what information the system is try to tell me. I also realize I should've written this up in the maintenance log; as we clearly exceeded AOM limitations.


Second narrative: When I did my preflight I clearly did not see that the fuel cross feed valve had been opened up; the Captain did not notice this either. We departed our flight to ZZZ1 with cross feed open. Fuel config enunciation illuminated several times but neither of us noticed the position of the cross feed valve at that time. As I called for flaps 25 on the approach to ZZZ1; I noticed yoke was a little toward left wing down but aircraft was flying fine. Captain and I then noticed the fuel imbalance and cross feed open. We were approximately 1000 ft AGL and decided to continue without any changes. The left wing showed approximately 2300 pounds and the right 11;600. At about 500 AGL or lower we received the low fuel illumination. Landed without any other issues. After shutdown in the gateway; Captain and I talked about how such an event like this happened or be missed; also how we could prevent an event from happening in the future. Whenever a fuel config light illuminates there is a reason why or cause; we should definitely look around and make sure we know why it illuminated. Expectation bias probably took over and we should never let our guard down. I will be much more vigilant in a situation like this one when I observe the a fuel config light is cancelled or removed.


Synopsis: Air Carrier flight crew reported inadvertently leaving a fuel crossfeed valve open; resulting in a fuel imbalance.