ON LNDG FLARE ILS RWY 18L; DFW; B757 FLC WAS REQUIRED TO TAKE ACTION TO CORRECT FOR LATERAL MOVEMENT CAUSED BY A B777 TAXIING ONTO RWY.

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ILS RWY 18L AT DFW. WX WAS 500 OVERCAST WITH 3 MILES VIS. APCH WAS FLOWN ON AUTOPLT TO 400 FT AND THEN HAND FLOWN TO TOUCHDOWN. PRIOR TO SHORT FINAL; TWR HAD CLRED A BOEING 777 TO CROSS 18L AND HOLD SHORT OF 18R. AS WE APCHED THE THRESHOLD; BELOW 50 FT TWR CLRED THE B777 TO TAKE POSITION ON 18R. AS WE FLARED AND BEGAN TO RETARD OUR POWER THE B777 APPARENTLY THROTTLED UP. AT 5 FT IN THE FLARE WITH THROTTLES IDLE; WE CAUGHT THE BRUNT OF THE B777'S POWER SURGE AND FOUND OURSELVES GOING FROM SMOOTH TO TURBULENT AIR AND BEING BLOWN SIDEWAYS. THE CHANGE IN FLT CONDITIONS WAS RATHER ABRUPT; BUT WE MANAGED TO CORRECT AND LAND SAFELY. AFTER GATE ARR; I SPOKE WITH W TWR SUPVR WHO TOLD ME THAT BECAUSE OF THE CONSTRUCTION ON THE W SIDE; WHICH WILL LAST ANOTHER YEAR; THEY HAVE GONE TO USING THE OUTSIDE FOR DEPARTURES AND THE INSIDE RWY FOR TKOFS; AND THAT OUR SIT IS NOT THAT UNCOMMON. HE ALSO SAID THAT TWR TRIES TO AVOID THE CONFLICT THAT WE ENCOUNTERED; BUT IT STILL OCCURS. NEEDLESS TO SAY; I BELIEVE THAT THE OPERATION COULD EVENTUALLY LEAD TO AN ACFT BEING BLOWN OFF THE RWY DURING LNDG IF THE PROC IS NOT CHANGED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT IN VMC CONDITIONS; THE FLT CREW NATURALLY WOULD HAVE OBSERVED THE B777'S POSITION AND MOST LIKELY WOULD HAVE ACCOMMODATED FOR THE POTENTIAL OF JET BLAST. THE CAPT ADVISED HE WAS 5 TO 10 FT IN THE FLARE; REDUCING PWR AND ALMOST AT ENG IDLE. HE ADVISED HE WAS ON NORMAL APCH GLIDE PATH. HIS GREATEST CONCERN IS DURING POOR WX CONDITIONS; WHEN ACFT TYPE COULD NOT IMMEDIATELY BE RECOGNIZED; THEN INCURRING JET BLAST ON FLARE OUT; ESPECIALLY WHEN NOT RECEIVING A CAUTION ADVISORY BY ATC FOR THE TAXIING ACFT JET BLAST. DURING DISCUSSION WITH THE TWR SUPVR; THE SUPVR ADVISED THAT DFW HAD RECEIVED OTHER SIMILAR CALLS FROM PLTS CONCERNING THE SAME JET BLAST ENCOUNTER. THE CAPT WAS ADVISED TO EXPECT THIS CONDITION FOR ANOTHER 18 MONTHS OR UNTIL THE RWY 18R CONSTRUCTION IS COMPLETED.