Date: 201602
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dusk
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Leading Edge Slat
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Executed Go Around / Missed Approach; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: On descent into ZZZ on an extended left base under vectors by Approach we were instructed to reduce speed to 210 kts. I was PF and flying manually. As we slowed I requested flaps 1; then flaps 5. We were following a 737 and were asked to further reduce to 170 kts. As we slowed I noticed a brief moment where the PLI came down to the aircraft attitude indicator and the top of the amber foot rose to the aircraft attitude indicator and then the moved back to normal positions. I mentioned this to the FO but he didn't notice it since he was switching frequencies. This was odd because we had plenty of margin between our target airspeed and the PLI/FOOT. As we slowed further I asked for flaps 15 and then 20. It seemed that the airplane did not want to slow down as we began our descent visually using the glide slope. This seemed odd to me and to avoid increasing airspeed I opted for gear down and further landing flap settings. We selected flaps 25 and I noticed that the PLI and Amber foot again pinched in very close the target airspeed. I asked for flaps 30 and at that moment we received the 'LE SLAT ASSYM' alert accompanied by a rumbling that I felt in the control column. The airplane just didn't feel right to me. I would estimate we were around 2500 AGL and we opted to go-around. We conducted normal go-around procedures which leads us to retract flaps to 20 which we did. I hand flew the go-around as I felt it prudent to maintain a feel for the airplane not knowing exactly what we had going on with respect to the wing. We climbed to 4;000 and asked Approach for extended vectors to stay within 30 miles of field. Fuel at that time of the go-around was around 10;600 pounds which was on target for planned FOD. On the go-around we decided to clean up to flaps 5/190 kts. During clean-up I could feel a rolling moment as the flaps approached 5 degrees. I asked that the flaps be placed back to 20 since the aircraft handling in my opinion was ok at that configuration. We split the cockpit up and I had my FO work the QRH while I flew and talked. Working through a rather lengthy and confusing checklist we arrived at the conclusion that we had a leading edge asymmetry issue and would attempt a landing with a Flaps 30+30 speed but a configuration of flaps 20 this due to my concern that when we were previously at flaps 30; we had an aerodynamic rumble associated with sporadic PLI/Amber foot indications. As we received vectors I employed one of our jumpseaters that was seated in the first observer's seat to assist in any way she felt she could. She was very helpful with her input and concurrently we decided to transfer aircraft control so I could look the checklist over to ensure we had covered everything. Feeling satisfied with that I reassumed control of the aircraft and with the full support of my first-officer began to set up for the ILS to the longest runway. The configuration we would fly the approach resulted in a higher than normal approach speed of 172 kts so we agreed the longer runway was the wise choice. We also elected to have the CFR standing by for possible hot brakes and informed them of our intentions after landing. At this time I noted the fuel was 7200 pounds and we were 25 miles from the field heading back. Seeing this I [advised ATC of our low fuel state] as well and requested a direct vector to the outer marker which Approach provided. We configured the aircraft per QRH procedures and shot the approach/landing hand flown at flaps 20. We pre-briefed tail-strike awareness due to odd landing configuration/speed and used max auto brakes. I noted no odd PLI/Amber foot anomalies at this configuration/speed as well as no rolling tendency. The pitch and feel seemed normal on the approach. Landing was uneventful. We cleared the runway and waited for CFR to inspect the aircraft. No hot-spots/smoke noted so we taxied in leaving flaps in their current position to assist maintenance in their post flight inspection.I must absolutely praise my first officer for his assistance during this situation. His valuable and timely input added tremendously to the positive outcome. From a human factors perspective he was flawless. He also provided valuable systems knowledge that helped in assessing our situation. I must also thank TRACON for their excellent assistance providing us exactly what we asked for and when we asked for it.Please add to the description above that I intended to say the PLI was coming down to the aircraft attitude while the amber foot was coming up to the target speed. I erred with my description above a couple times suggesting the amber foot was approaching aircraft attitude.


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


Synopsis: B767-300 flight crew reported landing with a leading edge slat asymmetry problem.