FO; UNAWARE HE FAILED TO FULLY ENGAGE THE AUTOPLT; IS UNAWARE THAT THE ACFT IS CLBING ABOVE ASSIGNED ALT.

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WE WERE PROCEEDING DIRECT TO KNOX (OXI) VOR/DME USING RNAV. WE WERE CRUISING AT FL250 AND HAD JUST BEEN TOLD TO DSND TO 14000 FT MSL. SINCE THE RNAV CAN ONLY BE COUPLED TO THE #1 AUTOPLT; AND I WANTED TO USE MY OWN #2 AUTOPLT (IN ORDER TO COUPLE IT TO MY OWN #2 VOR); I DISENGAGED THE #1 AUTOPLT AND ENGAGED THE #2 AUTOPLT. WHEN YOU SWITCH FROM ONE AUTOPLT TO THE OTHER; YOU MUST RE-ENGAGE BOTH THE AUTOPLT AND AUTOTHROTTLES. WHEN I TRIED TO RE- ENGAGE THE AUTOTHROTTLE AND #2 AUTOPLT; I DIDN'T NOTICE THAT THE #2 AUTOPLT DID NOT ENGAGE. I FOCUSED MY ATTN ON THE FLT DIRECTOR PANEL AND PROGRAMMED A 2000 FPM DSCNT; NOT NOTICING THAT THE VSI AND ALTIMETER WERE SHOWING A CLB. MY FIRST CLUE THAT SOMETHING WAS WRONG CAME WHEN THE AUTOTHROTTLES ADVANCED PWR. INITIALLY; I BELIEVED THERE WAS AN AUTOTHROTTLE MALFUNCTION SINCE THE THROTTLES SHOULD HAVE RETARDED FOR THE DSCNT. IN REALITY; SINCE THE #2 AUTOPLT WAS NOT ENGAGED; IT ALLOWED THE ACFT TO START A CLB. THE CLB CAUSED THE AIRSPD TO BLEED OFF; AND THE AUTOTHROTTLES PROPERLY ADVANCED; WHICH CAUSED THE AIRPLANE TO CLB EVEN MORE RAPIDLY. AT ABOUT FL255; I DISENGAGED BOTH THE AUTOTHROTTLES AND AUTOPLT (NOT REALIZING THE AUTOPLT WAS NOT ENGAGED). WE REACHED ABOUT FL256 BEFORE I COULD ESTABLISH THE DSCNT. I THEN TOLD THE CAPT THAT I BELIEVED WE HAD AN AUTOTHROTTLE AND AUTOPLT MALFUNCTION. FOR A WHILE; HE DIDN'T SAY MUCH. I CONTINUED TO PUZZLE AT HOW THIS FAILURE OF AUTOTHROTTLE AND AUTOPLT COULD OCCUR. AT ONE POINT; I SAID; 'I WISH I KNEW WHAT HAD HAPPENED.' HE THEN SAID THAT HE COULD TELL ME WHAT HAPPENED. I INVITED HIM TO EXPLAIN. HE WENT ON TO LIST THE EVENTS IN DETAIL. I WAS DUMBFOUNDED TO LEARN HE ALLOWED THIS CHAIN OF EVENTS TO CONTINUE. I ASKED HIM WHY HE DIDN'T DO OR SAY ANYTHING ABOUT THE SIT. HE SAID HE TOLD ME ONCE THAT WE WERE 200 FT HIGH. I TOLD HIM THAT I DIDN'T HEAR HIS ALERT AND WONDERED WHY HE DIDN'T DO OR SAY ANYTHING MORE. HE RESPONDED BY SAYING THAT HE DIDN'T WANT TO UPSET ME BY APPEARING TO 'DIRECT' ME AS I HAD COMPLAINED OF 2 DAYS EARLIER. 2 DAYS EARLIER THE CAPT DIRECTED ME ON WHEN TO DSND; TURN AND REDUCE AIRSPD ON A VISUAL APCH INTO LA GUARDIA; NY. I TOLD HIM THEN THAT I FELT HE WAS TOO DIRECTIVE IN A SIT WHERE PLT TECHNIQUE WAS INVOLVED; AND NO CONFLICT WAS IMMINENT.