Narrative:

On the RNAV visual runway xxr into ZZZ at around 1;800 feet AGL; I asked for flaps 15. I glanced at the flap indication 15 and le flaps ext light green. A few seconds later received an airspeed low call out from the aircraft. I checked my airspeed at around 175-180; so I glanced at the flap setting which showed flaps 15. The problem we had was the green le flap ext and the yellow le flap transit where alternating between yellow and green. We executed a go-around and requested extended vectors to run the checklist. I informed the flight attendant that we had a flap issue and would be landing shortly in ZZZ. I also made a short PA to the passengers. At 10;000 feet on radar vectors; we got into the qrc. We ran the leading edge flaps transit checklist. The interesting part was the le flap ext and the le flap transit lights continued to alternate between green and yellow. The le devices indicated all devices in the green. We ran the checklist which directed a flaps 15 landing. Ran perf wb for the 15 flap data for runway xxr at ZZZ; and also ran break cooling data. Made sure we were both comfortable with our plan to land [runway] xxr and taxi clear. We landed [runway] xxr waited to apply brakes and taxied clear. Brake cooling directed us not to approach the gate for 30 minutes; so we held out until the 30 minute time had expired. I gave a call to dispatch and maintenance while we waited for our gate. Maintenance took the aircraft from us and ran a few tests. They found that leading edge flap #4 had an issue. They set the flaps to 15 and also got the alternating yellow and green lights with all le devices showing green. They did mention a code for le flap #4 was showing a problem. The first officer and I headed over to our next flight.

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Original NASA ASRS Text

Title: B737-700 Captain reported a mechanical problem with a portion of the leading edge flap.

Narrative: On the RNAV Visual Runway XXR into ZZZ at around 1;800 feet AGL; I asked for flaps 15. I glanced at the flap indication 15 and LE FLAPS EXT light green. A few seconds later received an Airspeed Low call out from the aircraft. I checked my airspeed at around 175-180; so I glanced at the flap setting which showed flaps 15. The problem we had was the green LE FLAP EXT and the yellow LE FLAP TRANSIT where alternating between yellow and green. We executed a go-around and requested extended vectors to run the checklist. I informed the Flight Attendant that we had a flap issue and would be landing shortly in ZZZ. I also made a short PA to the passengers. At 10;000 feet on radar vectors; we got into the QRC. We ran the LEADING EDGE FLAPS TRANSIT Checklist. The interesting part was the LE FLAP EXT and the LE FLAP TRANSIT lights continued to alternate between green and yellow. The LE DEVICES indicated all devices in the green. We ran the checklist which directed a flaps 15 landing. Ran Perf WB for the 15 flap data for Runway XXR at ZZZ; and also ran break cooling data. Made sure we were both comfortable with our plan to land [Runway] XXR and taxi clear. We landed [Runway] XXR waited to apply brakes and taxied clear. Brake cooling directed us not to approach the gate for 30 minutes; so we held out until the 30 minute time had expired. I gave a call to Dispatch and Maintenance while we waited for our gate. Maintenance took the aircraft from us and ran a few tests. They found that leading edge flap #4 had an issue. They set the flaps to 15 and also got the alternating yellow and green lights with all LE DEVICES showing green. They did mention a code for LE FLAP #4 was showing a problem. The First Officer and I headed over to our next flight.

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.