A B737-700 captain reported encountering wake turbulence from a preceding B747 on a parallel runway ...

Narrative:

We were approximately 25 miles out for 24R [at lax] when ATC crossed a B747 at ten miles for 24L. The surface winds were a crosswind from right to left; but the winds at altitude were left to right; which must have kept the B747's jet wash lingering in our approach path. I flew slightly high; but still encountered the turbulence at about 15 miles at about 4;500 ft. I believe we were at flaps 5 slowing to 170 KTS per ATC. We rolled abruptly to the left; but only about 20 degrees before the autopilot was disengaged. The remainder of the approach was flown by hand; slightly steep (1/2 dot or so) until about 1;000 ft AGL. As we were below 10;000 ft in a sterile cockpit; I did not make a PA. We landed without incident and turned off at the reverse and immediately crossed 24L per the tower. The taxi was short and very congested and; again; I did not stop the aircraft to make a PA. Once safely parked at our gate; I made myself available at the front of the aircraft to answer customer questions. There were a few; but no one seemed overly agitated or alarmed. [It's] nearly impossible to consistently predict where jet wash will be encountered; even if protective measures are taken; as we did. Next time; I may elect to go-around. This is the first time socal approach has placed a B747 across my final at lax (probably with good intentions on their part).

Original NASA ASRS Text

Title: A B737-700 Captain reported encountering wake turbulence from a preceding B747 on a parallel runway at LAX.

Narrative: We were approximately 25 miles out for 24R [at LAX] when ATC crossed a B747 at ten miles for 24L. The surface winds were a crosswind from right to left; but the winds at altitude were left to right; which must have kept the B747's jet wash lingering in our approach path. I flew slightly high; but still encountered the turbulence at about 15 miles at about 4;500 FT. I believe we were at flaps 5 slowing to 170 KTS per ATC. We rolled abruptly to the left; but only about 20 degrees before the autopilot was disengaged. The remainder of the approach was flown by hand; slightly steep (1/2 dot or so) until about 1;000 FT AGL. As we were below 10;000 FT in a sterile cockpit; I did not make a PA. We landed without incident and turned off at the reverse and immediately crossed 24L per the Tower. The taxi was short and very congested and; again; I did not stop the aircraft to make a PA. Once safely parked at our gate; I made myself available at the front of the aircraft to answer customer questions. There were a few; but no one seemed overly agitated or alarmed. [It's] nearly impossible to consistently predict where jet wash will be encountered; even if protective measures are taken; as we did. Next time; I may elect to go-around. This is the first time SoCal Approach has placed a B747 across my final at LAX (probably with good intentions on their part).

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	931862
Time
Date	201101
Local Time Of Day	1201-1800
Place
Locale Reference	LAX.Airport
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach Final Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Final Approach Initial Approach
Flight Plan	IFR
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 200 Flight Crew Type 12000
Events
Anomaly	Inflight Event / Encounter Wake Vortex Encounter

A B737-700 captain reported encountering wake turbulence from a preceding B747 on a parallel runway at lax.