Yesterday, July 16, 1999, while in Mexico City(MEX), i observed an Air France B747-428(SCD) F-GISE in a quite unusual situation. The aircraft arrived, and departed with only one winglet!!! It took quite a few doubletakes, and binoculars to confirm my original vision. The left wingtip was simply gone. The hole where it should have been attached was quite evident. THe opposite side was normal. I would think that this would cause asymetrical flight and handeling difficulties, but no attention was paid to the wing during the aircraft's apx 2 hr stay at MEX. Does anyone know what happened, or how this type of incident affects flight characteristics?