A B747-100 DEPARTING OUT OF SEOUL; KOREA; HAS AN NMAC WITH MIL FIGHTER.

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AT XX28Z CLBING OUT OF SEOUL; KOREA; IMC; PASSING APPROX FL140; WE PASSED WITHIN ABOUT 300 FT OF A FLT OF 2 ACFT. TCASII SOUNDED TO DSND AND WE DSNDED SHARPLY. IN ABOUT 2 SECONDS; THE TCASII SOUNDED TO RESUME CLB; WHICH WE DID. THE 2 ACFT WERE OBSERVED ON THE TCASII SCREEN TO BE AT 200 FT AND 300 FT; RESPECTIVELY; ABOVE US. WE QUERIED ATC AND THEY STATED THERE WAS VFR TFC IN THAT AREA BUT ATC WOULD NOT TELL US WHO THEY WERE. WE ADVISED KOREA ATC OF THE NEAR MISS. FLT PROGRESSED NORMALLY ON TO NARITA. RTE G597 IS A 1-WAY ROUTING FOR DEPS LEAVING SEOUL. QUITE OFTEN; ACFT APPEAR ON THIS RTE ON THE TCASII WITHOUT ELEVATION READOUTS. THE RTE NEEDS TO BE DEDICATED TO CIVIL DEP ACFT OR ELSE ANOTHER RTE NEEDS TO BE SPECIFIED. THE CLOSURE RATE IN THIS NEAR MISS WAS AROUND 800 KTS AND TO MISS AT 300 FT IS TERRIBLE! SUPPLEMENTAL INFO FROM ACN 377669: DURING CLBOUT ON G597; DEP CTL GAVE US A TA; 'TFC AT 10 O'CLOCK.' THERE WAS AN AREA OF NUMEROUS TARGETS AT APPROX 20 NM. DUE TO THE DENSITY OF TARGETS; THEIR ALTS COULD NOT BE DELINEATED. ABOUT 20 SECONDS LATER; A TARGET WAS READ AT APPROX 10 MI AND 1200 FT ABOVE AT 11 O'CLOCK. I SUGGESTED TO PF; 'WE SHOULD LEVEL OFF BRIEFLY.' HE STARTED TO DECREASE THE CLB. ATC CALLED AGAIN; 'TFC AT 11 O'CLOCK.' TCASII ALERT; 'DSND!' THE PLT COMMENCED THE AVOIDANCE MANEUVER. INITIAL DSCNT RATE 1500 FPM DOWN. THE TFC WAS OBSERVED ON TCASII SCREEN AT +200/+300 (2 TARGETS) 200 FT AND 300 FT ABOVE US. WE WERE JUST ENTERING AN AREA OF CLOUDS AND NEVER SAW THE TFC. THE HORIZ SEPARATION WAS NOT CLR ON THE SCREEN; POSSIBLY 0- 400 YARDS OFF THE L SIDE. TOTAL TIME FROM FIRST WARNING BY ATC TILL END OF INCIDENT WAS 1 MIN OR LESS. CTR: 'WHO WAS THE TFC WE JUST MISSED?' THE ANSWER WAS; 'IT WAS VFR TFC NOT IN THEIR CTL.' IN 30 YRS OF FLYING; THIS WAS PERHAPS THE 'CLOSEST CALL' I'VE EVER HAD! VFR TFC FLYING UNCTLED ON AN AIRWAY WILL EVENTUALLY CAUSE DISASTROUS RESULTS! SUPPLEMENTAL INFO FROM ACN 377470: CLBING OUT OF SEL; IMC; PASSING APPROX 14000 FT; WE PASSED WITHIN ABOUT 300 FT OF A FLT OF 2 ACFT. TCASII SOUNDED TO DSND AND THE PLTS DSNDED. IN ABOUT 2 SECONDS; THE TCASII SOUNDED TO RESUME CLB; WHICH THE PLTS DID. THE 2 ACFT WERE OBSERVED ON THE TCASII SCREEN TO BE AT 200 FT AND 300 FT; RESPECTIVELY; ABOVE US. THE ONLY WAY TO PREVENT THIS TYPE OF INCIDENT FROM HAPPENING AGAIN; IS TO RESTRICT VFR MIL TFC FROM FLYING NEAR THE AIRWAYS.