FLC FAILS TO COMPLY WITH ATC ALT RESTR.

Narrative

WE WERE CRUISING AT FL330 ON A CLOUDLESS DAY. WE WERE IN THE VICINITY OF RDU VORTAC ON THE JET RTE BTWN RDU AND RIC WHEN ZDC CLRED US TO CROSS 85 MI SW OF RIC AT FL270. AS IS OUR AIRLINE'S PROC; I; AS THE PF USING AUTOPLT; SET AND ARMED FL270 IN THE DFGS. THE PNF XCHKED FL270 SET AND ARMED IN DFGS. THE CLRNC WAS GIVEN ABOUT 130 DME FROM THE RIC VORTAC. I WROTE THE CLRNC ON MY NOTE PAPER AND MADE A MENTAL NOTE TO BEGIN A DSCNT AT ABOUT 110 DME FROM RIC. THE PNF AND I THEN RESUMED A CONVERSATION ABOUT VARIOUS MATTERS INCLUDING RECENT LABOR AGREEMENTS WITH OUR COMPANY. AT ABOUT 90 DME FROM RIC; ZDC SAID 'ARE YOU GOING TO BE ABLE TO MAKE THAT RESTR?' WE REPLIED IN THE NEGATIVE AT WHICH TIME WE BEGAN A DSCNT FROM FL330 TO FL270. ZDC THEN SAID; '...DSND NORMAL RATE TO FL270....' WE ACKNOWLEDGED AND REACHED FL270 75 DME SW OF RIC VORTAC. THIS INCIDENT WAS CAUSED BY MY FORGETTING ABOUT THE ALT RESTR. MY PERFORMANCE MAY HAVE BEEN AFFECTED BY SEVERAL FACTORS: 1) LACK OF SLEEP. I SLEPT ABOUT 5-6 HRS ON EACH OF THE 2 PREVIOUS NIGHTS AND OUR FIRST FLT ON THE DAY OF THE INCIDENT DEPARTED AT XA45. 2) TIME OF DAY. I SEEM TO BE MORE FATIGUED ON TRIPS IN THE EARLY AFTERNOON. 3) DISTRS. MY THOUGHT PROCESS ABOUT DSCNT PLANNING MAY HAVE BEEN INTERRUPTED SOMEHOW BY MY CONVERSATION WITH THE OTHER PLT OR BY LOOKING OUTSIDE THE COCKPIT WINDOWS AT FAMILIAR LANDMARKS. I COULD PROBABLY PREVENT FURTHER RECURRENCES OF THIS SIT BY EITHER UTILIZING THE PMS TO PERFORM THE DSCNT; OR ON XING RESTR DSCNTS DONE WITHOUT PMS; KEEPING THE DME READOUT FIRMLY IN MY XCHK UNTIL THE DSCNT IS COMPLETED.