Date: 201512
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: Mixed
Weather elements / visibility: 5
Light: Dusk
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Trailing Edge Flap
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: The flight was unremarkable until configuring the flaps [for] landing. We were cleared for an ILS approach to 4R. The aircraft was stabilized on glideslope and on course at 170 knots approximately eight miles from the runway. I was the Captain and the First Officer was the Pilot Flying. The aircraft was cleared to land and was configured with the flaps set to five and the landing gear down. The Pilot Flying (PF) asked for flaps 15. As I moved the flap lever from the five detent to 15; the aircraft experienced a sudden un-commanded roll to the right. The First Officer (FO) disconnected the autopilot as the aircraft rolled through 30 degrees of bank. At the same time I moved the flaps back to the five detent. The FO recovered to a wings level attitude and I informed Tower we needed a heading and altitude as we had to break off the approach.  Tower told us to climb to 3000 feet and contact Approach Control. Once the aircraft was climbing; we decided to raise the gear but keep the flaps down. I asked the FO to take over the radios and continue flying while I worked the QRH. We briefly discussed what we thought the problem was; and what could have caused the roll. We briefly considered wake turbulence; but decided it was more likely a flap malfunction or failure as we were not close to the preceding aircraft on final.  It took me a few minutes to decide which checklist to run from the QRH. (Most of the excellent information that was in the old QRH is difficult to find as it is not tabbed by system.). I knew that the older model 737s have an un-commanded roll QRC checklist; but the -700 QRH does not address this. I did find a reference to un-commanded roll at the beginning of the Trailing Edge Flap Asymmetry Checklist. It was only one bullet point; but I decided this checklist was the best one to use for an un-commanded roll after flaps are moved.  We ran all of the items for the checklist through the 'Before Landing' portion. I also notified the Flight Attendants and Passengers; sent an ACARS message to Dispatch; [notified] ATC.  The FO gave me control of the aircraft on a ten mile left downwind. He then reviewed the QRH to make sure everything was accomplished correctly. We finished configuring the aircraft and left the flaps at five for the landing.I have never landed less than 30 flaps; except for in the simulator; so I was not sure what to expect. I used the HUD on final; and had to keep the thrust levers near idle to keep from getting fast on glidepath. The flare and touchdown didn't seem very different from a flaps 30 landing. We taxied clear and told Tower we did not need any further assistance.  We taxied to the gate and finished the shutdown and parking procedures like any other flight; except we opted to keep the flaps at five in case they were damaged.  I did call Dispatch and Maintenance Control and entered the flap discrepancy in the logbook. One thing I did not do was pull the cockpit voice recorder circuit breaker. (I did not look at the event reporting chart until after I was at the hotel and did not realize I was supposed to.)As far as prevention goes; I do not have a suggestion. However; training for the event and QRH guidance could be improved. It was very stressful trying to find un-commanded roll guidance in the -700 QRH. I did not feel it was appropriate to study the AOM while burning what little gas we had left with the flaps stuck down. Perhaps a blurb could be entered in the flight control tab directing the Pilot to various conditions that might cause the roll. Also if it is important for me to pull the circuit breaker on the CRV maybe Company could emphasize this during training; or have Maintenance Control and/or Dispatch help remind the pilots.


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


Synopsis: B737-700 flight crew reported experiencing an uncommanded roll during flap extension on approach. Flight landed with flaps set to position 5.