WDB ACFT ON DSCNT MISSES XING RESTRICTION.

Narrative

AT FL260 CTR GAVE US A RESTRICTION TO CROSS SOMTO INTXN AT 11000 FT. THE FO WAS FLYING (MYSELF) AND THE CAPT READ BACK THE RESTRICTION. I PROGRAMMED THE FMS TO CROSS SOMTO AT 11000. AT THE TIME THE CLRNC WAS RECEIVED; WE WERE APPROX 40 MI S OF SOMTO. THE FMS CAPTURED VNAV PATH AND BEGAN TO DSND. THE CAPT EXCUSED HIMSELF TO USE THE LAVATORY DSNDING. WHILE HE WAS AWAY; I BEGAN TO PROGRAM THE APCH INTO LGA. WHEN I WAS FINISHED; I WENT TO THE DSCNT PAGE ON THE FMC IN ORDER TO CHK THE PROGRESS OF OUR DSCNT. I NOTICED THAT THE FMC WAS PREDICATING THE DSCNT ON DIALS AT 2500 FT; AN ALT WHICH I HAD PROGRAMMED IN FOR THE APCH. AT THAT MOMENT; I TURNED TO THE DIRECT INTERCEPT TO SEE DISTANCE FROM SOMTO. I OBSERVED THAT WE WERE 13 MI S OF SOMTO AT FL210. I IMMEDIATELY CALLED CTR TO CONFIRM SOMTO AT 11000 FT. THE CTLR ISSUED AN IMMEDIATE TURN TO HDG 180 DEGS. DURING THIS CLRNC THE CAPT RETURNED TO THE COCKPIT. I IMMEDIATELY MADE A R AND INCREASED THE RATE OF DSCNT TO OVER 6000 FPM. AFTER ABOUT 30 DEGS OF TURN; CTR TURNED US BACK TO THE N TO INTERCEPT THE NANCI ARR N OF SOMTO. ONE OF THE MISTAKES I MADE WAS ASSUMING THAT AFTER THE ACFT CAPTURED VNAV PATH IN THE DSCNT THAT IT WOULD MAKE THE XING RESTRICTION AND REQUIRE NO SUPERVISION. WHEN I PUT THE 2500 FT ALT AT DIALS IN; SOMEHOW THE FMC ACCEPTED THAT AS ITS XING RESTRICTION. IT IS POSSIBLE THAT I MAY HAVE ERRED WITH MY INPUT; BUT I DON'T KNOW HOW. ANOTHER MISTAKE WAS CHANGING FROM THE MAP DISPLAY TO THE PLAN DISPLAY IN PROGRAMMING THE APCH. WITH 1 PLT OUT OF THE SEAT AND THE OTHER IN THE PLAN MODE; THERE IS CERTAINLY DIMINISHED POS AWARENESS. NO AMOUNT OF TECHNOLOGY RELIEVES THE PLTS OF THEIR DUTIES OF BASIC AIRMANSHIP. TECHNOLOGICAL ADVANCEMENTS HAVE IN MY OPINION GREATLY ENHANCED AND IMPROVED VIRTUALLY ALL FACETS OF AVIATION; HOWEVER; ERRORS WILL STILL BE MADE BY BOTH THE MACHINERY AND THE PLTS WHO CTL THE MACHINERY AND IN THIS PARTICULAR INCIDENT; COMPLACENCY WAS CERTAINLY A FACTOR.