Date: 201811
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Light Wind; 10
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Flap/Slat Control System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting
Second reporter function: Pilot Flying; Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was the Pilot Flying during the second and last leg of the third day of a four-day pairing. The weather was day; VMC with 10+ miles of visibility and light winds. We were approaching ZZZ descending through 9;000 feet for a right base; visual approach to Runway XXR backed up by the ILS; cleared direct to ZZZZZ. The Captain programmed a hard altitude of 2;400 feet MSL at ZZZZZ so that we would get an accurate vertical profile. As we descended into the field; I began slowing and configuring; using flaps in conjunction with speed brakes as I was approximately 1;500 feet high on profile. While decelerating; I called for Flaps 5; then 10; and gear down. I felt like the aircraft wasn't responding as it usually did; (it wasn't correcting down on profile and I was still high) as I had a fair amount of drag out; so I decided to hand fly it and level off; slow up; and then come down.I called for Flaps 15; noting the airspeed around 195 knots. At this point; we both noticed that the flap position indicator was stuck between 0 and 1; with the amber Leading Edge Flaps Transit light illuminated; and then heard the Airspeed Low Warning. We did not receive a stick shaker or buffet. The flap selector handle was at 15 [degrees] and did not agree with the indicator; which was stuck between 0 and 1. I added power and we initially leveled off at 5;000 feet. The aft overhead Leading Edge Devices annunciator panel indicated that LE Flaps were fully extended and LE Slats were extended and all green indication capsules on the annunciation panel. We communicated to Approach Control that we needed vectors to run a few checklists and sort out a problem with our flaps.We diagnosed a trailing edge flap disagree situation; (there was no asymmetry) and then completed the Trailing Edge Flap Disagree Checklist. The Pilot Monitoring (Captain) ran the [Weight and Balance System] numbers for a Flaps 15 landing with the Trailing Edge Flaps Disagree abnormal. I notified the flight attendants of the flap abnormality and relayed that we would need to run several checklists and it would take a while; but that we did not anticipate an evacuation.We received a descent to 3;000 feet and help from Approach with vectors for a box pattern while we ran checklists. Once we leveled off at 3;000 feet; I re-engaged the autopilot in heading mode with 210 knots selected in the speed window. It was then that I realized that we still had the landing gear down; so we retracted the gear to reduce fuel burn and drag while completing checklists. The Captain took control of the aircraft at this point; and became the Pilot Flying. The Captain [requested priority] and requested that Fire Rescue Equipment be standing by for our landing.With the Captain's concurrence; I made a brief announcement to the passengers regarding an abnormality that required us to run several checklists; and that they might see fire trucks by the runway after landing as a precaution. We completed the Alternate Flap Extension Checklist and Before Landing Checklist; and had an uneventful Flaps 15 landing on Runway XXR; exiting the runway and running the brake cooling module in [the Weight and Balance System] as the Fire Rescue trucks examined the aircraft for any smoking brakes. The Fire Crew reported that everything looked normal.The [Weight and Balance System's] brake cooling module indicated that we were cleared to park at the gate; so we proceeded to the gate with the Fire Rescue trucks in escort. Once parked; we deplaned the passengers. I completed a post flight walk around and did not notice any apparent fluid leaks or damage to any flight control surfaces.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Air carrier flight crew reported noticing the flaps were not extending during approach and ran the QRH. Priority landing was requested; aircraft landed without incident at a reduced flaps setting.