Narrative:

While being vectored for visual approach to runway xx at ZZZ; the first officer called for flaps 5. I set the flap handle to 5 and about the same time ATC called our base turn. It was shortly afterward that I realized the flaps had barely moved; even though the handle was in the 5 detent. The indicators were split; 1 at 0; and the other at about 1/2 degree (I don't recall left/right). I pointed this out to the first officer and we agreed to abandon the approach and work the problem through the QRH. While being vectored by ATC; we referenced the trailing edge flap asymmetry checklist. This checklist directed us to bring the flap handle back to the up position; which in turn led us to the trailing edge flaps up landing checklist. At that point I made sure the first officer had the flight controls and ATC; and I contacted dispatch/maintenance through ZZZ operations frequency. I informed them of our condition and told them we would probably need to divert to ZZZ1 in order to have a longer runway. We began to run weight and balance numbers and brake cooling data for runway xy at ZZZ1. Dispatch was doing the same; but also ran numbers for runway xx at ZZZ. They informed us that we would have a stopping margin of about 1;500 ft. With autobrake max. We went ahead and confirmed this by running the numbers ourselves; but neither one of us was comfortable landing on the shorter runway because we also had the number 2 thrust reverser inoperative. This was something that was already on an MEL. Another big concern was brake cooling and potential for blowing tire fuse plugs.we both felt like the safest and most conservative choice was the longer runway at ZZZ1. I was fully aware that it would be inconvenient for everyone involved but had to remind myself of our operational priorities and their order. Dispatch; ATC; flight attendants; and passengers were all fully informed of our situation. We [requested priority handling] with ATC and requested vectors for a 25 mile final to give us time to finish the QRH procedures which required us to deploy the leading edge flaps via the alternate method. I assumed control of the aircraft about 35 miles from the airport. We finished the QRH and made the high speed approach and landing on runway xy without incident. Crash fire rescue equipment (crash fire rescue) was waiting and we had them inspect the tires and brakes. They noted nothing of concern and based on my brake application at about 130 kts.; we were able to proceed to a gate that had been coordinated for us. On shutdown we noted low b-system quantity of 74 and an RF displayed. Defects were entered in the logbook and per coordination from the operations center; the passengers and crew eventually deplaned; cleared immigration and customs; and boarded ground transportation for ZZZ.this was just an unfortunate flap malfunction. I don't think it was preventable.

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Original NASA ASRS Text

Title: B737 flight crew reported a flap extension failure that resulted in a diversion.

Narrative: While being vectored for Visual Approach to Runway XX at ZZZ; the First Officer called for Flaps 5. I set the Flap Handle to 5 and about the same time ATC called our base turn. It was shortly afterward that I realized the flaps had barely moved; even though the handle was in the 5 detent. The indicators were split; 1 at 0; and the other at about 1/2 degree (I don't recall L/R). I pointed this out to the First Officer and we agreed to abandon the approach and work the problem through the QRH. While being vectored by ATC; we referenced the Trailing Edge Flap Asymmetry Checklist. This checklist directed us to bring the flap handle back to the Up position; which in turn led us to the Trailing Edge Flaps Up Landing Checklist. At that point I made sure the First Officer had the flight controls and ATC; and I contacted Dispatch/Maintenance through ZZZ OPS frequency. I informed them of our condition and told them we would probably need to divert to ZZZ1 in order to have a longer runway. We began to run weight and balance numbers and brake cooling data for Runway XY at ZZZ1. Dispatch was doing the same; but also ran numbers for Runway XX at ZZZ. They informed us that we would have a stopping margin of about 1;500 ft. with Autobrake Max. We went ahead and confirmed this by running the numbers ourselves; but neither one of us was comfortable landing on the shorter runway because we also had the Number 2 thrust reverser inoperative. This was something that was already on an MEL. Another big concern was brake cooling and potential for blowing tire fuse plugs.We both felt like the safest and most conservative choice was the longer runway at ZZZ1. I was fully aware that it would be inconvenient for everyone involved but had to remind myself of our operational priorities and their order. Dispatch; ATC; Flight Attendants; and Passengers were all fully informed of our situation. We [requested priority handling] with ATC and requested vectors for a 25 mile final to give us time to finish the QRH procedures which required us to deploy the leading edge flaps via the alternate method. I assumed control of the aircraft about 35 miles from the airport. We finished the QRH and made the high speed approach and landing on Runway XY without incident. CFR (Crash Fire Rescue) was waiting and we had them inspect the tires and brakes. They noted nothing of concern and based on my brake application at about 130 kts.; we were able to proceed to a gate that had been coordinated for us. On shutdown we noted low B-system quantity of 74 and an RF displayed. Defects were entered in the logbook and per coordination from the Operations Center; the passengers and crew eventually deplaned; cleared Immigration and Customs; and boarded ground transportation for ZZZ.This was just an unfortunate flap malfunction. I don't think it was preventable.

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.