The B737-300 encountered wake turbulence from a preceding B757; which appeared to have disconnected ...

Attributes
ACN	844596
Time
Date	200907
Local Time Of Day	1201-1800
Place
Locale Reference	SADDE
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR SADDE
Component
Aircraft Component	Autoflight System
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 172 Flight Crew Type 12000
Person 2
Function	First Officer
Experience	Flight Crew Last 90 Days 164
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types Inflight Event / Encounter Wake Vortex Encounter

Narrative:

We were on the sadde six arrival into lax. Early on the arrival ATC advised us we were following a heavy 757 and to be aware of wake turbulence. Between symon and sadde we experienced the wake turbulence from the preceding 757 about 20 miles ahead. We were leveling at 10;000 ft. As we were approaching sadde from the north; I noticed LNAV was no longer selected. No mode was selected and I told the first officer to come left to smo. This occurred at .6 NM north of sadde. Seconds later approach asked us if we were in a turn to smo and further vectored us left 050 to intercept the arrival to smo. Our delay in the turn probably put us closer to the departure corridor than expected. I believe that the jolts from the wake turbulence kicked off LNAV. I haven't experienced this phenomenon before; if accurate. Nonetheless; I feel I should have checked systems more thoroughly and more timely after a wake turbulence event to ensure no changes occurred.

Original NASA ASRS Text

Title: The B737-300 encountered wake turbulence from a preceding B757; which appeared to have disconnected the LNAV function of the auto flight system.

Narrative: We were on the SADDE SIX arrival into LAX. Early on the arrival ATC advised us we were following a heavy 757 and to be aware of wake turbulence. Between SYMON and SADDE we experienced the wake turbulence from the preceding 757 about 20 miles ahead. We were leveling at 10;000 FT. As we were approaching SADDE from the north; I noticed LNAV was no longer selected. No mode was selected and I told the First Officer to come left to SMO. This occurred at .6 NM north of SADDE. Seconds later Approach asked us if we were in a turn to SMO and further vectored us left 050 to intercept the arrival to SMO. Our delay in the turn probably put us closer to the Departure corridor than expected. I believe that the jolts from the wake turbulence kicked off LNAV. I haven't experienced this phenomenon before; if accurate. Nonetheless; I feel I should have checked systems more thoroughly and more timely after a wake turbulence event to ensure no changes occurred.

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.