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A dc-9 captain reported significant wake vortex-induced roll on approach behind a B747-800.
| Attributes | |
| ACN | 1040637 |
| Time | |
| Date | 201210 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ANC.Airport |
| State Reference | AK |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | DC-9 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Landing |
| Route In Use | Visual Approach |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | B747-800 Advanced |
| Flight Phase | Landing |
| Person 1 | |
| Function | Pilot Flying Captain |
| Qualification | Flight Crew Flight Engineer Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP) |
| Events | |
| Anomaly | Inflight Event / Encounter Wake Vortex Encounter |
Narrative:
[We were] following a B747-800 into anchorage. I hand flew one dot above the glide slope. The winds were calm at the surface. I know how to avoid wake turbulence and was in VFR conditions arriving at least 4-5 miles behind the newer 800 type 747's. Around 200 ft or less; I had the dc-9 roll rapidly to the right; descend; and the aircraft offset from the centerline. I regained control and realigned and landed. I told the tower controller that I experienced some type of wake and she said she knows; said she saw what happened. I would have to assume that the 747 was coupled for the landing; just by the way I viewed the stable and steady state approach. My questions are: does the 800; newer wing; have some unknown new wake characteristic where it stays longer or reacts differently than the standard wing? Did boeing make an assumption without proofs or was it theoretical? Could the large vertical stab/rudder create a vortices that will not dissipate even after touch down; unlike the wings. Could a rudder input (during flare) cause a pressure change to develop vortices that high off the ground? We can agree that the V/south is symmetrical until an input is applied. A wing wake should have rolled me; but what about the large vertical surface?
Original NASA ASRS Text
Title: A DC-9 Captain reported significant wake vortex-induced roll on approach behind a B747-800.
Narrative: [We were] following a B747-800 into Anchorage. I hand flew one dot above the glide slope. The winds were calm at the surface. I know how to avoid wake turbulence and was in VFR conditions arriving at least 4-5 miles behind the newer 800 type 747's. Around 200 FT or less; I had the DC-9 roll rapidly to the right; descend; and the aircraft offset from the centerline. I regained control and realigned and landed. I told the Tower Controller that I experienced some type of wake and she said she knows; said she saw what happened. I would have to assume that the 747 was coupled for the landing; just by the way I viewed the stable and steady state approach. My questions are: Does the 800; newer wing; have some unknown new wake characteristic where it stays longer or reacts differently than the standard wing? Did Boeing make an assumption without proofs or was it theoretical? Could the large vertical stab/rudder create a vortices that will not dissipate even after touch down; unlike the wings. Could a rudder input (during flare) cause a pressure change to develop vortices that high off the ground? We can agree that the V/S is symmetrical until an input is applied. A wing wake should have rolled me; but what about the large vertical surface?
Data retrieved from NASA's ASRS site as of July 2013 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.