BE20 PLT CLBING TO FL200 BECOMES DISTR; OVERSHOT ASSIGNED ALT; AND CONFLICTS WITH MIL TFC AT FL210.

Narrative

I WAS CLRED TO CLB TO FL200. I HAD THE AUTOPLT ENGAGED; AND AS I APCHED MY ASSIGNED ALT; THE AUTOPLT ANNUNCIATED ALT CAPTURE. I WAS THEN DISTR BY PROGRAMMING A WAYPOINT INTO THE GPS. THE OTHER ACFT (A MARINE ACFT) CALLED ZDC ASKING ABOUT TFC ON RADAR. HE SAID HE HAD AN RA AND WAS CLBING. CTR CTLR ASKED ME FOR MY ALT. IT WAS INDICATING BTWN FL206 AND FL207. I IMMEDIATELY DSNDED BACK TO ALT OF FL200. THE AUTOPLT HAD NOT ACTUALLY CAPTURED THE ALT; BUT HAD NOT ANNUNCIATED ANY MALFUNCTION. THE NEXT CTLR ASKED ME TO CALL THE ZDC SUPVR WHEN I LANDED; WHICH I DID. THE AUTOPLT HAD SEVERAL MOMENTARY 'AUTOPLT TRIM FAIL' LIGHT ANNUNCIATIONS LATER IN THE FLT. THESE OCCURRENCES WERE RPTED FOR MAINT ACTION. MY DISTR WITH GPS WAYPOINT ENTRY AND RELIANCE ON THE AUTOPLT AUTOMATED ALT CAPTURE FUNCTION CAUSED THIS SIT. I WAS TOLD BY THE CTR SUPVR THAT THE CONFLICT WAS CAPTURED BY THEIR SYS ELECTRONICALLY. THE MARINE ACFT HAD CLBED TO FL213; WHILE I WAS AT FL207; A DIFFERENCE OF 600 FT. MY ACFT IS NOT TCASII EQUIPPED. FORTUNATELY; THE MARINE ACFT HAD TCASII.