Narrative:

I was the flying pilot and had configured to flaps 10; holding 180 kts until just before the bridge; and then asked for gear down; flaps 15 and the landing checklist. Since my ref speed was 133 knots; I bugged the speed back to 138 kts. At approximately 150 kts I called for flaps 30 and then shortly after called for flaps 40. It quickly became apparent the aircraft was not slowing as I expected and then my first officer called; 'flap asymmetry.' the left flap was at approx 16 and the right flap was at approx 12. I was now approaching 1000 AGL and decided that we would need to go around and give ourselves more time to sort out our problem. I also thought it ill advised to try a landing at ZZZ not knowing my flap condition. We advised ATC we were going around and they gave us an immediate left turn out of the pattern and a climb to 3000'. In the go around; I called for flaps 5 and held out speed at 180 kts. The first officer moved the flap control lever to 5; but the flaps remained fixed at 16/12. We did retract the gear and I called for the first officer to get out the QRH and perform the flap asymmetry emergency procedure. I flew and talked with ATC; while the first officer talked with the flight attendants/passengers; and completed the QRH procedures. A minute or so after our departure from the pattern; ATC asked us to climb to 4000'. I started to climb; but felt the aircraft rolling right and the flaps retracted to 5 without us moving the lever. I stopped the climb and decided we needed to get on the ground as soon as possible. I told ATC we were unable to climb; I was declaring an emergency and that I wanted vectors to ZZZ1 and their longest runway. Then without warning; the gear horn sounded. With flaps at 5 and the gear up; we decided to lower the gear to get rid of the horn and proceeded with flaps 5; gear down and being vectored to ZZZ1. We landed with a ref speed of 162 kts with auto brakes set to max and max reversing on touchdown. I let the aircraft roll to the end of the runway before I exited; brought the aircraft to a stop; shut down the engines and asked crash fire rescue equipment to inspect the wheels; tires; brakes and gear for heat and damage. After about 5 minutes; crash fire rescue equipment indicated they found no damage and fairly normal heat for our situation and suggested we could slowly taxi to the gate. To aid crash fire rescue equipment in their inspection; I ordered the flaps to be retracted and they did come up when commanded.

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Original NASA ASRS Text

Title: A B737-400 encountered a flap asymmetry situation and diverted to an airport with a longer runway. Flaps retracted normally after landing.

Narrative: I was the Flying Pilot and had configured to flaps 10; holding 180 kts until just before the bridge; and then asked for gear down; flaps 15 and the landing checklist. Since my ref speed was 133 knots; I bugged the speed back to 138 kts. At approximately 150 kts I called for flaps 30 and then shortly after called for flaps 40. It quickly became apparent the aircraft was not slowing as I expected and then my First Officer called; 'Flap Asymmetry.' The left flap was at approx 16 and the right flap was at approx 12. I was now approaching 1000 AGL and decided that we would need to go around and give ourselves more time to sort out our problem. I also thought it ill advised to try a landing at ZZZ not knowing my flap condition. We advised ATC we were going around and they gave us an immediate left turn out of the pattern and a climb to 3000'. In the go around; I called for flaps 5 and held out speed at 180 kts. The First Officer moved the flap control lever to 5; but the flaps remained fixed at 16/12. We did retract the gear and I called for the First Officer to get out the QRH and perform the flap asymmetry emergency procedure. I flew and talked with ATC; while the First Officer talked with the flight attendants/passengers; and completed the QRH procedures. A minute or so after our departure from the pattern; ATC asked us to climb to 4000'. I started to climb; but felt the aircraft rolling right and the flaps retracted to 5 without us moving the lever. I stopped the climb and decided we needed to get on the ground ASAP. I told ATC we were unable to climb; I was declaring an emergency and that I wanted vectors to ZZZ1 and their longest runway. Then without warning; the gear horn sounded. With flaps at 5 and the gear up; we decided to lower the gear to get rid of the horn and proceeded with flaps 5; gear down and being vectored to ZZZ1. We landed with a ref speed of 162 kts with auto brakes set to max and max reversing on touchdown. I let the aircraft roll to the end of the runway before I exited; brought the aircraft to a stop; shut down the engines and asked CFR to inspect the wheels; tires; brakes and gear for heat and damage. After about 5 minutes; CFR indicated they found no damage and fairly normal heat for our situation and suggested we could slowly taxi to the gate. To aid CFR in their inspection; I ordered the flaps to be retracted and they did come up when commanded.

Data retrieved from NASA's ASRS site as of April 2012 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.