FLC ON ARR DSNDS BELOW ASSIGNED ALT.

Narrative

I HAD BEEN FLYING INTO DFW ALL MONTH USING THE 'BOIDS' ARR AND LNDG S (XING RHOME AT 9000 FT). THIS PARTICULAR FLT; DFW WAS LNDG N WHICH MEANT OUR CLRNC WAS TO CROSS 'DIDLY' AT 11000 FT. DURING THE DSCNT ATC CLRED US TO CROSS DIDLY AT 11000 FT WHICH WAS SET IN THE ALT WINDOW OF THE FLT GUIDANCE PANEL. AS I APCHED 11000 FT I BEGAN TO SLOW TO 250 KTS. THE FO WENT OFF FREQ TO GET THE ATIS WHILE I WAS LOOKING FOR TFC; ALL THE TIME THINKING I HAD TO BE AT 9000 FT IN JUST A FEW MI. I LEFT 11000 FT TO DSND TO 9000 FT. AT 10700 FT I GOT THE ALT WARNING AT WHICH TIME THE FO SAID 'OUR CLRNC IS TO 11000 FT.' I IMMEDIATELY BEGAN THE RECOVERY TO 11000 FT. ATC DID NOT MENTION THE DEV AND ALT 'LOSS' WAS NO MORE THAN 400 FT. I STILL CANNOT EXPLAIN WHY IT HAPPENED OTHER THAN A HIGH WORKLOAD PERIOD; A 9000 FT MINDSET ON MY PART AND HABIT OF BEING ASSIGNED 9000 FT ON THAT PARTICULAR ARR. SUPPLEMENTAL INFO FROM ACN 328603: THE DEV OCCURRED DUE TO FOLLOWING ROUTINE/FAMILIAR HABIT PATTERNS DURING A HIGH WORKLOAD PERIOD WHEN THE 'PNF' WAS NOT MONITORING.