ALTDEV ALT EXCURSION - ACR CREW CLBS INSTEAD OF DSNDING AS THE CLRNC REQUIRED.

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I WAS THE PF; FMC WAS IN VNAV AND HDG. WE WERE VFR AVOIDING A TSTM CLRED DIRECT SJI WHEN ABLE. AS WE PASSED TSTM; I EXECUTED A DIRECT SJI AND ENGAGED LNAV. CTR CLRED US TO FL240 PLT'S DISCRETION AFTER FL290; SELECTED 24000 FT; SELECTED 24000 FT IN ALT WINDOW AND SELECTED THEN ENGAGED 'CAPTURE' IN THE VNAV MODE. ACFT STARTED A DSCNT AND CTR CLRED US TO AN INTXN. WE WERE UNABLE TO FIND THE FIX ON THE HIGH CHART; ASKED CTR FOR SPELLING; WAS NOT IN NAV DATABASE. I FOUND THE FIX ON THE LOW CHART; ASKED FO TO PUT IT IN NAV PAGE; I HAD TO DEFINE FIX TO THE FMC AND GOT THE ACFT ON RTE. AS I ENGAGED LNAV; CTR ASKED OUR ALT. FO REPLIED 33500 FT DSNDING; WHILE I WAS DEFINING AND GETTING THE FMC TO GO DIRECT; VNAV DISENGAGED. I WAS SURE DSCNT WOULD CONTINUE IN VERT SPD MODE; BUT PITCH COMMAND WAS ANNUNCIATED; AUTOPLT HAD NO PITCH EXCEPT CTL WHEEL STEERING. ACFT STARTED A SLIGHT CLB; CORRECTED AND MADE PROPER DSCNT; NO FURTHER EVENTS. FACTORS: FIRST LEG OF FLT SERIES; NEW FO JUST OUT OF INITIAL OPERATING EXPERIENCE. HE DIDN'T KNOW HOW TO FINE THE FIX AND HAD PROBS WITH FMC USE. HE WAS KEENLY WATCHING WHAT I WAS DOING AND PAID NO ATTN TO FLT PROFILE. I WAS OVERLOADED DUE TO HAVING TO DO ALL THE WORK MYSELF. AUTOFLT HAD SOME REOCCURRING PROBS THE REST OF THE DAY; OCCASIONAL PITCH OR ROLL CTL WHEEL STEERING ANNUNCIATED DURING FMC FLT. I ASSUME THIS WAS NOT NORMAL; BUT COULDN'T DUPLICATE PROBS. IT WAS JUST AN INTERMITTENT PROB; AND CORRECTED ITSELF ON THE THIRD LEG. I SUSPECT A POSSIBLE ALIGNMENT ERROR CAUSED BY IMPROPER ALIGN PROCS DONE BY FO. WHEN I DID A FULL ALIGNMENT ON THE THIRD LEG; NO FURTHER PROBS.