SEPARATION MINIMA WAS LOST AS A FLC; DISTRACTED BY TFC; FAILED TO RECOGNIZE AN AUTOFLT ALT CAPTURE FAILURE.

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WHILE CLBING ENRTE FROM CAK TO SYR WE WERE TOLD BY ATC TO LEVEL OFF AT 16000 FT. I SELECTED 16000 FT ON THE ALT PRE-SELECT AND ALT PRE-SELECT WAS SELECTED ON THE AUTOPLT. AS WE APCHED 16000 FT ATC CALLED TFC XING FROM L TO R AT 17000 FT. WE RPTED THE TFC IN SIGHT. AT ABOUT THIS TIME I THOUGHT I NOTICED THE ACFT LEVELING OFF AT 16000 FT; ALTHOUGH I DID NOT CONFIRM THAT THE AUTOPLT HAD CAPTURED 16000 FT. SHORTLY AFTER THIS I NOTICED THE ACFT STILL CLBING AT ABOUT 16200 FT. I SELECTED ALT HOLD ON THE AUTOPLT AT WHICH TIME THE ACFT PITCHED DOWN ABRUPTLY AND THEN UP. I DISCONNECTED THE AUTOPLT AND LEVELED OFF AND THEN RETURNED TO 16000 FT. WHILE THIS WAS HAPPENING; ATC REQUESTED OUR ALT AND MY COPLT RPTED 16300 FT. THAT WAS OUR HIGHEST OBSERVED ALT. THE TFC WAS IN SIGHT ALWAYS AND NO ACTION WAS NECESSARY TO AVOID A CONFLICT WITH THIS ACFT. ATC THEN REQUESTED THAT WE CALL THEM AT (217) 774- 0329 WHEN WE LANDED AT SYR. WHEN I CONTACTED THEM THEY ADVISED ME THAT THEY HAD NOT HAD THEIR MINIMUM SEPARATION REQUIREMENTS BTWN OUR 2 ACFT AND THAT A RPT WOULD HAVE TO BE FILED WITH THE FAA. I BELIEVE THERE WERE SEVERAL CONTRIBUTING FACTORS IN THIS INCIDENT: FAILURE ON MY PART TO CONFIRM THAT THE AUTOPLT HAD CAPTURED THE SELECTED ALT. ATTN WAS DIVERTED OUTSIDE THE COCKPIT AT A CRITICAL TIME WHEN WE TRIED TO LOCATE THE RPTED TFC. ALTHOUGH I HAVE MANY HRS FLYING THIS TYPE OF ACFT; I HAD NOT FLOWN THIS PARTICULAR ACFT IN SEVERAL MONTHS AND WAS NOT AWARE THAT AUTOPLT SOMETIMES PORPOISES WHEN IT LEVELS OFF. THIS WAS THE SECOND LEG OF AN EARLY MORNING FLT WHICH HAD FOLLOWED A LONG DAY AND A SHORT NIGHT. I DID NOT FEEL AS SHARP AS I NORMALLY DO ON A FLT AND I'M SURE MY COPLT WAS EXPERIENCING SOME FATIGUE AS HE HAD BEEN WITH ME ON THE PREVIOUS FLT. SUPPLEMENTAL INFO FROM ACN 300978: I CALLED ONE TO GO AS THE ACFT CLBED THROUGH 15000 FT. ZOB CALLED TFC 12 O'CLOCK 17000 FT. I RPTED LOOKING NEGATIVE CONTACT. ZOB CALLED TFC 2 O'CLOCK; 17000 FT SBOUND. I RPTED TFC IN SIGHT; AT WHICH TIME THE ALT ALERT SOUNDED; INDICATING 16300 FT AND CLBING. THE PF DISENGAGED AUTOPLT AND LEVELED OFF AT APPROX 16500 FT. MY CONCERN WAS TWOFOLD; FIRST; ALT AWARENESS; SECOND; TFC AWARENESS. I FEEL AS PNF I DID THE RIGHT THING. I CALLED ONE TO GO TO ALERT PF OF ALT AWARENESS; AFTER WHICH I WAS CONTINUALLY LOOKING OUTSIDE OF THE ACFT FOR TFC.