FMC PROGRAMMED FOR AN 'EXPECT' CLRNC BEGAN DSCNT PRIOR TO ACTUAL ATC CLRNC. CTLR INTERVENED.

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DURING A ROUTINE FLT WE WERE CLRED DIRECT TO LAMMA INTXN ON THE BITHO 6 ARR INTO ORL. THE ARR STATES TO 'EXPECT TO CROSS LAMMA INTXN AT 12000 FT.' CONSEQUENTLY; I PROGRAMMED THE FMC TO CROSS LAMMA INTXN AT 12000 FT. PRIOR TO RECEIVING A DSCNT CLRNC THE ACFT BEGAN TO DSND BASED ON THE COMPUTER TOP OF DSCNT POINT. THE CAPT; WHO HAD LEFT THE COCKPIT FOR PHYSIOLOGICAL REASONS; WAS JUST GETTING BACK INTO HIS SEAT. ZJX THEN ASKED US WHAT OUR ALT WAS. AT THIS TIME I REALIZED WE WERE NEVER CLRED TO LEAVE FL310 AND HENCE; STARTED A CLB BACK TO FL310. THE CTLR THEN CLRED US TO CROSS LAMMA INTXN AT 12000 FT. WHEN ASKED ABOUT THE ALTDEV THE CTLR STATED; 'DON'T WORRY ABOUT IT.' THE CONTRIBUTING FACTORS TO THIS EVENT ARE AS FOLLOWS. THE CREW FLEW TO SAME DEST ALL MONTH AND WAS ROUTINELY CLRED TO CROSS A FIX AT SAME ALT. WE WERE PREPROGRAMMED MENTALLY FOR SUCH ACTION. A 2-MAN COCKPIT LENDS ITSELF TO ERRORS WHEN NO BACKUP IS AVAILABLE IF 1 OF THE CREW LEAVES THE COCKPIT. THE PLT WITH LOW TIME OPERATING EXPERIENCE IN A SOPHISTICATED ACFT THAT IS COMPUTER OPERATED INADVERTENTLY PROGRAMMED COMPUTER IMPROPERLY. 3 AREAS THAT MAY BE CONSIDERED TO PREVENT THIS FROM HAPPENING ARE RE-WORD ALT XING RESTRS ON DEP AND ARRS SUCH AS: ELIMINATE THE PHRASE 'EXPECT TO CROSS AT' AND REPLACE WITH 'CROSS AT; ONLY IF RADIO CONTACT FAILURE.' RE-EXAMINE COMPANY PROCS WITH REGARD TO PROGRAMMING FMC'S. ANALYZE AIM PROCS WITH REGARD TO CLRNCS GIVEN TO 2-MAN CREWS WHEN 1 CREW MEMBER IS OUT OF THE COCKPIT.