Narrative:

Our aircraft, an large transport, was following a widebody transport on the ILS DME runway 05R in mexico city. The WX was good with a left crosswind of 20 KTS. Approaching the OM, the widebody transport had already touched down and was rolling out, giving at least 5 mi spacing. The approach was in choppy air, and the tower called landing winds of 10 KTS, so I added 10 KTS to the approach speed. Everything was proceeding normally until passing the threshold, on the GS, the aircraft rolled left, then right but was not initially, a fast or unusual occurrence. Then, the aircraft unexpectedly rolled hard first one direction and then another while the nose pitched up and down. Extreme control movements were required to level the wings and keep them level. I advanced power to go around when the wake turbulence suddenly ceased. The captain touched the throttles indicating we should land. We were in a good position to continue the landing, however, the airspeed was bug plus 10 KTS (about 140 KTS) at touchdown. We made a normal landing but used more braking than usual due to 1. High ground speed due to density altitude (mexico city elevation 7341 ft) 2. Left thrust reverser inoperative dispatch. 3. Adrenaline. We exited the runway at 'B' highspd taxiway with approximately 2000 ft runway remaining. In this situation, everything happened so quickly that everything was reaction. My guess is that the 10 KTS of wind was a direct X and served to keep the widebody transport wingtip vortices on the runway -- setting up a potentially fatal situation. Had this been recognized earlier, flying slightly above the GS might have prevented this experience. Legal spacing does not guarantee safety!

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Original NASA ASRS Text

Title: LGT FOLLOWING WDB FOR LNDG ENCOUNTERS WAKE TURB WHICH CAUSES EXTREME ROLL AND PITCH MOVEMENTS.

Narrative: OUR ACFT, AN LGT, WAS FOLLOWING A WDB ON THE ILS DME RWY 05R IN MEXICO CITY. THE WX WAS GOOD WITH A L XWIND OF 20 KTS. APCHING THE OM, THE WDB HAD ALREADY TOUCHED DOWN AND WAS ROLLING OUT, GIVING AT LEAST 5 MI SPACING. THE APCH WAS IN CHOPPY AIR, AND THE TWR CALLED LNDG WINDS OF 10 KTS, SO I ADDED 10 KTS TO THE APCH SPD. EVERYTHING WAS PROCEEDING NORMALLY UNTIL PASSING THE THRESHOLD, ON THE GS, THE ACFT ROLLED L, THEN R BUT WAS NOT INITIALLY, A FAST OR UNUSUAL OCCURRENCE. THEN, THE ACFT UNEXPECTEDLY ROLLED HARD FIRST ONE DIRECTION AND THEN ANOTHER WHILE THE NOSE PITCHED UP AND DOWN. EXTREME CTL MOVEMENTS WERE REQUIRED TO LEVEL THE WINGS AND KEEP THEM LEVEL. I ADVANCED PWR TO GAR WHEN THE WAKE TURB SUDDENLY CEASED. THE CAPT TOUCHED THE THROTTLES INDICATING WE SHOULD LAND. WE WERE IN A GOOD POS TO CONTINUE THE LNDG, HOWEVER, THE AIRSPD WAS BUG PLUS 10 KTS (ABOUT 140 KTS) AT TOUCHDOWN. WE MADE A NORMAL LNDG BUT USED MORE BRAKING THAN USUAL DUE TO 1. HIGH GND SPD DUE TO DENSITY ALT (MEXICO CITY ELEVATION 7341 FT) 2. L THRUST REVERSER INOP DISPATCH. 3. ADRENALINE. WE EXITED THE RWY AT 'B' HIGHSPD TAXIWAY WITH APPROX 2000 FT RWY REMAINING. IN THIS SITUATION, EVERYTHING HAPPENED SO QUICKLY THAT EVERYTHING WAS REACTION. MY GUESS IS THAT THE 10 KTS OF WIND WAS A DIRECT X AND SERVED TO KEEP THE WDB WINGTIP VORTICES ON THE RWY -- SETTING UP A POTENTIALLY FATAL SITUATION. HAD THIS BEEN RECOGNIZED EARLIER, FLYING SLIGHTLY ABOVE THE GS MIGHT HAVE PREVENTED THIS EXPERIENCE. LEGAL SPACING DOES NOT GUARANTEE SAFETY!

Data retrieved from NASA's ASRS site as of July 2007 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.