Narrative:

While on the sunst 4 arrival into las; we encountered unexpected wake turbulence while in and out of the clouds. The encounter was rapid and equivalent to moderate chop; lasting approximately three seconds. Although the seat belt sign was on in the cabin; the flight attendants were still up securing the cabin for arrival. I told the first officer [that] I was going to check on them; and he had the radios (in addition to his pilot flying duties). Thankfully; no one was hurt; and I returned to my duties as pilot monitoring. Shortly thereafter; we both noticed the aircraft was no longer in LNAV. I directed an immediate return to course and noticed our cross track error was approximately 3 NM. While correcting to course between bty and mycal; la center called and noted our left turn back on course. I advised them of the wake turbulence encounter and that our LNAV apparently disengaged as a result. They then directed us to proceed directly to mycal and descend via the arrival. The rest of the arrival into las was uneventful.since neither the first officer nor I recall an uncoordinated change in navigation mode; we can only attribute the exiting of LNAV to the wake turbulence encounter. My immediate concern was the safety of the flight attendants and passengers; and I failed to note the navigation mode change in a timely manner as the pilot monitoring. In the future; I will ensure the aircraft is still in the proper mode following such an encounter.

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Original NASA ASRS Text

Title: B737-700 Captain reported a track deviation occurred when LNAV disconnected as a result of a wake turbulence encounter descending into LAS.

Narrative: While on the SUNST 4 Arrival into LAS; we encountered unexpected wake turbulence while in and out of the clouds. The encounter was rapid and equivalent to moderate chop; lasting approximately three seconds. Although the seat belt sign was on in the cabin; the Flight Attendants were still up securing the cabin for arrival. I told the First Officer [that] I was going to check on them; and he had the radios (in addition to his Pilot Flying duties). Thankfully; no one was hurt; and I returned to my duties as Pilot Monitoring. Shortly thereafter; we both noticed the aircraft was no longer in LNAV. I directed an immediate return to course and noticed our cross track error was approximately 3 NM. While correcting to course between BTY and MYCAL; LA Center called and noted our left turn back on course. I advised them of the wake turbulence encounter and that our LNAV apparently disengaged as a result. They then directed us to proceed directly to MYCAL and descend via the arrival. The rest of the arrival into LAS was uneventful.Since neither the First Officer nor I recall an uncoordinated change in navigation mode; we can only attribute the exiting of LNAV to the wake turbulence encounter. My immediate concern was the safety of the Flight Attendants and passengers; and I failed to note the navigation mode change in a timely manner as the Pilot Monitoring. In the future; I will ensure the aircraft is still in the proper mode following such an encounter.

Data retrieved from NASA's ASRS site 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.