DC-9 Undifferentiated or Other Model
Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer
Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Regained Aircraft Control
Environment - Non Weather Related; Procedure; Aircraft
[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?
A DC-9 Captain reported significant wake vortex-induced roll on approach behind a B747-800.