B737-800
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Total 18250
Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Requested ATC Assistance / Clarification
Environment - Non Weather Related; Procedure
While being vectored for a night visual approach to Runway 28L at SFO; we encountered wake turbulence from a preceding B777. I would classify it as a moderate to moderate + wake turbulence encounter; lasting only 2-3 seconds. I was PM (Pilot Monitoring); FO (First Officer) was PF (Pilot Flying). We were vectored to 310 heading to intercept 28L final; I noted [the] B777 was 5.5 nm ahead; and NORCAL Approach had assigned that aircraft 180 KIAS to the marker/bridge DUYET. We were assigned 180 KIAS also. As we were capturing the final approach course for 28L; we encountered the moderate wake turbulence from the B777; which placed our aircraft in a momentary 15 degree left bank; followed by a 35-40 degree left bank; which disengaged the autopilot. The FO immediately took the controls and returned the aircraft to straight and level flight; stabilized. The left bank was only momentary; and the wake turbulence subsided. I noted that the B777 was only 4.5 nm ahead now; and surmised that they had slowed below 180 KIAS prior to DUYET; ignoring ATC instructions. We configured the gear & flaps and landed normally. I then called NORCAL Approach; discussed the incident with the sector supervisor; and debriefed the event with the FO. No further action taken. The event occurred in night VMC conditions on visual approaches to RWY 28L because the B777 had slowed below the 180 KIAS speed ATC assigned them to the marker (DUYET). Instead of 5.5 nm separation; we only had 4.5nm. I assume that ATC automatically assigns no less than 5 nm for smaller aircraft following a wide-body (heavy) aircraft. I believe it may be necessary to add at least 1 nm for added safety margin; if and when feasible; like on night visual approaches.
B737-800 Captain reported encountering wake turbulence on a night visual approach to SFO in trail of a B777.