A B747-200 HITS THE WAKE OF A B747-400 JUST AFTER TKOF FROM LAX. THE ACR FLC SAID THEIR ACFT ROLLED 25 DEGS TO THE L; BUT THEY WERE ABLE TO STOP THE ROLL AND RESTORE LEVEL ACFT ATTITUDE.

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WE WERE DEPARTING LAX FOR JTY IN A B747-200; TOGW WAS 768000 LBS. AN ACR B747-400 DEPARTED JUST AHEAD OF US. WE DELAYED FOR NORMAL HVY/HVY SEPARATION; AND MADE AN UNEVENTFUL TKOF. CLBING THROUGH ABOUT 1000 FT THE ACFT ROLLED HARD L ABOUT 25 DEGS; ACCOMPANIED BY SOME LIGHT CHOP. IMMEDIATE AILERON INPUT BROUGHT THE WINGS BACK TO LEVEL; AND THE REMAINDER OF THE SID WAS UNEVENTFUL. THE WIND WAS VERY LIGHT; CONDITIONS SMOOTH AND VFR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT HE WATCHED THE PRECEDING B747-400 TKOF; BUT HE DID NOT GIVE MUCH THOUGHT TO THE POSSIBILITY OF ENCOUNTERING WAKE TURB AND THE TWR CTLR DID NOT MENTION IT EITHER. EVERYONE IN THE COCKPIT WAS SURPRISED. THE CAPT SAID THAT THE WIND WAS FAIRLY CALM; HE DOES NOT KNOW THE EXACT SPD OR DIRECTION; AND THE VISIBILITY WAS GOOD. HE SAID THAT HE DOES NOT KNOW THE EXACT DISTANCE HE WAS BEHIND THE -400; BUT HE HAD HIS TCASII ON THE 6 MI RANGE DISPLAY AND WAS NOT SHOWING THE TARGET. HE DOES KNOW THAT HE TOOK OFF ABOUT 2; OR A LITTLE MORE; MINS AFTER THE - 400. THEY WERE STILL CONFIGURED FOR TKOF AND TKOF PWR WAS STILL ON THE ACFT. AFTER THIS ONE ENCOUNTER NO FURTHER WAKE EVENTS OCCURRED FOR THE REST OF THE FLT.