Date: 202109
Local time of day: 1201-1800
Location: A11.TRACON, AK
Aircraft: B737-900
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ANC
ATC / advisory: TRACON A11
Second aircraft: B747 Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness
Anomaly: Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Regained Aircraft Control; Flight Crew Took Evasive Action
Contributing factors: Environment - Non Weather Related; Human Factors; Procedure
Primary problem: Environment - Non Weather Related

Narrative: Wake turbulence encounter following a Boeing 747 on final approach. On radar downwind in VFR conditions we were cleared a visual approach following a 747 that was already established on final.  On the dog leg to final I was descending to arrive at the FAF at what would be a normal intercept for glideslope to runway 07R. Autopilot and autothrottles were connected at this time.  I noted on TCAS that we were 6 miles behind the heavy as we were about be aligned on final. Suddenly we encountered the wake turbulence from the preceding aircraft and the aircraft rolled quickly to the left. I took over controls manually and disconnected the autopilot and autothrottles while simultaneously recovering the airplane from the sharp bank to the left. The event happen very quickly; so I am unsure as to what bank angle we reached but estimating more than 30 and less than 45deg. We received a roll authority alert as the auto pilot had been unable to maintain level flight with the quick onset from the wake turbulence.  The aircraft recovered and we re-established ourselves on final. I mentioned to the First Officer that I was going to climb and maintain above the preceding aircraft flight path and also stay above glide slope for the remainder of the approach; planning to touchdown at 2;000 feet. The rest of the flight was uneventful and we landed normally in Anchorage.Looking back on this event I could have easily avoided encountering the wake turbulence.  When cleared for the visual approach behind the 747 I should've maintained my altitude instead of starting a gradual descent. I had plenty of time to descend later and descending at that time only increased the chances of encountering the wake. At the time; I was considering the fact that our distance was adequate and that we wouldn't have any issues following the 747 using normal visual cues /angle approaching the runway. I was wrong.  Even 6 miles behind the heavy the turbulence was strong and the rolling tendency abrupt. Not worth the risk; not to mention the discomfort to the passengers and crew. In the future I will certainly keep this in mind for a visual behind a preceding heavy aircraft to avoid this type of encounter.




Synopsis: B737-900 Captain reported encountering wake turbulence on approach to ANC in trail of a B747.