Date: 201509
Local time of day: 1201-1800
Location: LAX.Airport, CA
Flight conditions: VMC
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class B LAX
ATC / advisory: TRACON SCT
Second aircraft: B777 Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Human factors: Situational Awareness; Workload; Communication Breakdown
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was the pilot flying day VMC leg. Was told to expect 24L. From downwind over SMO was given a heading for base leg. On the issuance of the dog leg heading was told to follow traffic and I HEARD cleared visual '25L'. At about that time we encountered moderate wake turbulence. The autopilot came off and I continued to hand fly the aircraft through the landing.  I asked the First Officer (FO) 'it's 25L now?' 'Verify that' he asked ATC. I was told on the tape he read back 24L. I thought he told me 'yes 25L.' I saw traffic to follow on the 25 complex so flew over to align with 25L. It was clear when we got over there we were too close behind the traffic ahead. ATC asked if we saw the traffic 'for the south' and we answered in the affirmative. The FO even told ATC we could do S turns.  I told the FO 'no' it wouldn't work and that we had to go around. Before going around ATC specified we were cleared 24L and I finally comprehended that. We flew back over to 24L and landed uneventfully. The 25L traffic was quite close but we received no TCAS warning and all traffic was in sight. FO was brand new and had never flown into LAX on the SADDE arrival. He was rushed to reprogram the box for 25L and I even told him to just get the ILS freq. I suspect that once I made the move to 25L he became task saturated. In my experience runway switches to 25L on this arrival are not uncommon. This is especially true with the 24R closure. I misheard the visual approach clearance because I thought a runway change possible. The 'left' in the 24L clearance must have cued me to 25L as 'right' for a 24R clearance is the usual landing runway on north complex LAX.These comments are not meant to detract from my mistake miss hearing the approach clearance.  Apparently the FO read back 24L every time. But he never did direct me back to 24L or ask for clarification on what I was doing or had heard. I simply attribute that to him being new; but a more forceful approach by the FO would have cleared up my misunderstanding.Once I committed to the wrong runway ATC asked if I saw the traffic ahead; which is understandable; but didn't reconfirm the runway assignment; offer a heading or simply ask us what we were doing. Regarding the traffic they said 'he is for the south' which to me simply meant the south runway of the 25s; which confirmed we were too close to traffic landing on what I thought was our runway assignment. It did not convey that he was for 25L and I was cleared for 24L. Since the aircraft came off autopilot during the wake turbulence event I suppose I was a bit more task saturated by hand flying this entire time. I was also bit distracted since the FO was new.


Second narrative: I was now staring at the traffic and this; along with my preceding approx. 20 seconds heads down; lost my situational awareness in relation to the airport and did not immediately realize we were now lined up on the south side of the complex. I replied to ATC that we could try an 'S' turn but Captain said that wouldn't work and we should prepare to go around. It was then that I realized where we were. ATC said we were supposed to be lined up for 24L. Captain corrected back to 24L and the remainder of the approach and landing was uneventful.


Synopsis: A B737-800 flight crew reported wake turbulence on the SADDE arrival while given a; 'cleared visual Runway 25L' clearance.  Confusion between the Captain; First Officer ensued and they lined up for 25L after being cleared for visual to 24L.