The slats don't retract on a 747-400 takeoff for a long time after the acceleration height. At the Accel Ht, then the flap retraction process begins. You take off with Flaps 20 or Flaps 10. Then Flaps 5, then Flaps 1, then Flaps Up. In this accident, they never got the speed needed to even start the flap/slat retraction process.