LR60 ACFT ON CLB TO CRUISE WENT THROUGH ASSIGNED BY 450 FT WHEN CAPT RPTR ASSUMED THE ALT CAPTURE WOULD LEVEL ACFT. RPTR HAD INADVERTENTLY DISENGAGED THE AUTOPLT WHEN ROLLING THE ELEVATOR TRIM SWITCH.

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ON CLB TO CRUISE ALT FL230 THE CLB RATE WAS 3000 FPM. AUTOPLT SELECTED AND VERT MODE SELECTED. AT FL220 I 'BARRELED' THE TRIM SWITCH TO SLOW RATE OF CLB TO 1000 FPM. WITH ONLY 30 HRS IN THE NEW LEAR 60 I DIDN'T REALIZE THE ALT CAPTURE MODE WOULD ENGAGE SO EARLY (1000 FT). SINCE IT HAD ENGAGED; WHEN I TOGGLED THE TRIM TO SLOW RATE OF CLB I INADVERTENTLY KICKED OFF THE ALT CAPTURE MODE. AT 22500 FT WE GOT A CLRNC DIRECT TO DEST AND I BUSIED MYSELF CONFIGURING THE FMS FOR DIRECT TO DEST FLT. THIS DISTRACTED MY ATTN AND I BUSTED THE FL230 ALT CLRNC BY 450 FT BEFORE I REALIZED THE ERROR AND GOT BACK TO ASSIGNED ALT. THE COPLT CAUGHT THE ALT BUST. I JUST CAME FROM AN ACFT THAT WOULDN'T CLB AT SUCH A FAST RATE AND WOULDN'T GO TO ALT CAPTURE MODE BEFORE 500 FT PRIOR. MY LACK OF FAMILIARITY WITH THIS SYS; PLUS BEING DISTRACTED; PLUS HAVING AN OVER DEPENDENCE OR TRUST IN THE AUTOPLT SYS LED ME TO COMMIT THIS ERROR. IN THE FUTURE THE LEVELOFF MUST BE THE PRIME CONSIDERATION AND OCCUPATION UNTIL COMPLETE.