B737 flight crew reported executing a go-around after encountering wake turbulence from a preceding B747 while on final approach to ANC.
Synopsis
B737 flight crew reported executing a go-around after encountering wake turbulence from a preceding B747 while on final approach to ANC.
Narrative
This go-around event occurred at the end of ZZZ - ANC at approximately XC:30. We were projected for an on-time arrival prior to the go-around. I was the pilot flying. The planned arrival was PTERS 3 followed by radar vectors for ILS 15. Current ATIS reported at the time included winds 10007G21. Maximum wind additive of 15 kt. was added during descent planning. Weather during arrival was overcast at 9;000 - 10;000 ft. 10 SM visibility at the field. We experienced continuous light chop descending through 17;000 ft. Descending below 8;000 ft. we experienced increasingly heavier chop becoming continuous moderate turbulence. Our interval was a 747 at about 5.0 miles. Winds during the final approach were out of the east at 28 - 34 kt. with gusts descending through the final approach fix at approximately 1;500 ft. AGL. Tower reported the Runway 15 winds 100 at 11. We were fully configured at the FAF with all checklists completed and clearance to land.Descending through 1;200 ft. we experienced a severe patch of turbulence causing a roll to the right. The autopilot and autothrottle were both still engaged at the time of the roll. The FO and I assessed this roll to be associated with flying through the 747's wake turbulence. The autopilot corrected back to course by the 1;000-ft. call. We were stable with continuous light turbulence. Autopilot was disengaged approaching 500 ft. At the 500-ft. call; we were still stable and continued for the landing. Light chop with decreasing crosswinds. At 300 ft. the PAPIs showed three red and one white. At approximately 300 ft. the autothrottle was disengaged. Airspeed was 2 - 3 kt. above target speed at 150 kt.Descending through 150 ft.; the aircraft flew through an updraft/gust and became momentarily high on the glideslope. PAPIs showed one red and three white with a validated sight picture. At 100 ft.; airspeed had increased to 162 kt. and it became clear we would be long in the TDZ. An aural warning confirmed this and we executed a go-around for an unstable approach at approximately 60 - 50 ft.Climbing through 500 ft. on centerline; the continuous light to moderate chop returned. At 1;000 ft. on the climb-out; we experienced continuous moderate turbulence with an increasing left to right crosswind at 30+ kt. We continued to climb through what felt like a shear event with continuous moderate turbulence to moderate chop. Autopilot was still disengaged. During an ATC directed turn to 230 heading into the Turnagain Arm Bay low level turbulence area; we experienced moderate gusts from the south/southeast and momentarily exceeded 30 degrees AOB (Angle of Bank) with an aural warning. We continued through 3;000 ft. in an effort to find a better ride. During the climb we were getting airspeed gains and losses of 20 - 30 kt. The PM coordinated with Tower and Approach for altitudes and to return to ANC for a second approach.As we approached 5;000 ft.; the ride improved to constant light turbulence. Autopilot was engaged. The PM reset the FMC for the approach and completed required checklists. We proceeded to descend to 3;000 ft.; slow to 180 kt.; and configure. We were cleared for the visual approach to Runway 15. We backed ourselves up with the ILS 15. We were fully configured and stable at the FAF. Winds were 100 at 20 kt. and steady. Stable at 500 ft.; autopilot and autothrottle were disengaged. Approach; landing; and rollout were normal. During the entire event; the PM provided excellent crosscheck and verbal corrections while informing and coordinating with ATC; loading the FMC; and completing checklists. Excellent CRM/TEM (Threat and Error Management). At the gate and checklist complete; we contacted the Chief Pilot to make sure there were no required reports or follow-up actions.
Second reporter narrative
Coming into Anchorage; we were experiencing moderate turbulence. Captain was PF; and I was PM. We did a stabilized approach. At about 40 ft.; we got an updraft causing us to float down the runway. Captain called go-around; flaps 15; check thrust. So I put flaps 15. Captain called positive rate; gear up; set missed approach altitude. I put the gear up and confirmed 3000 for the missed. I then called ATC and said we were going missed because we were unstable. Captain then said level change; set clean maneuvering speed. I hit level change and then set clean maneuvering speed. I then realized level change didn't arm so I hit it again. After realizing it didn't arm a second time; I looked at the speed tape and noticed we were 195 kt. and accelerating towards the barber pole. I called check speed. Captain then told me flaps 5; flaps 1; flaps up. I put flaps 5 then 1 then up.I also then noticed we had no lateral guidance so I pointed it out to the Captain; he said he didn't have any. I then hit heading and turned the heading bug to the right to get him closer to the published missed. Heading mode wouldn't arm. So I tried LNAV and that wouldn't arm either. The Captain then turned right without the flight director being used. The Departure ATC Controller then gave us a heading so I set the heading bug to that. Then realized we were at 4;700 ft. so I said we need to descend so the Captain called for level change. I hit level change and it stayed in ALT ACQ (Altitude Acquired). I tried a second time and it did the same. ATC then asked us what altitude we wanted. I asked the Captain and he said 3;000 so I told ATC 3;000. ATC told us to descend. The Captain then started to descend. I then looked at the speed and noticed we were at 265 kt. I said airspeed and then the Captain corrected. The Captain then tried to turn the autopilot on. It disconnected instantly. He tried to turn the autopilot on a second time and had the same result. At this point I realized something was seriously wrong with the flight director. I told the Captain I was turning the flight directors off and then back on; then did so. The Captain then called for heading; level change; and autothrottles. All seemed to arm and work properly. He armed the autopilot. We then got stabilized to try the approach again. I reloaded the approach. I asked the Captain if he wanted me to talk to the flight attendants and passengers quick. He said yes so I did so. We then got vectors back to Runway 15 again and the rest was uneventful.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.