ACR OVERSHOOTS ALT ON PROFILE DSCNT TO YYZ; ON.

Narrative

DURING THE DSCNT INTO YYZ; WE WERE CLRED TO 7000 FT VIA THE PROFILE DSCNT FOR RWY 05/06R. THIS DSCNT REQUIRES A STEP-DOWN FIX AT 15 NM FROM YWT (12000 FT). THE ALT FOR THIS FIX IS AT OR BTWN 14000-12000 FT. WHEN CLRED TO 7000 FT; THE PNF SET THAT ALT IN THE ALT ALERTER AND THE DSCNT WAS STARTED. WE FAILED TO NOTICE THE LEVELOFF ALT REQUIRED BY THE PROC. AT 11500 FT WE WERE QUESTIONED BY THE CTLR ABOUT THE ALTDEV. WE WERE THEN CLRED TO 11000 FT AND THE PROFILE DSCNT. WE HAD DISCUSSED THE ARR WITH THE FO; EVEN ENTERED THE FIX 15 NM FROM YWT VOR AND THE XING RESTR OF 12000 FT. BUT; WE WERE VECTORED AWAY FROM OUR RTE AND THEN CLRED DIRECT YWT; THIS ERASED THE YWT -- 15 NM FIX FROM THE FMS. IT WAS LATER RE-ENTERED BUT WITHOUT ITS RESTR. IN ADDITION; THE CLRNC TO DSND TO 7000 FT TRIGGERED AN AUTOMATIC RESPONSE TO CROSS SUCH ALT INSTEAD OF THE APPROPRIATE STEP-DOWN FIX. I THINK IT WOULD BE LESS CONFUSING IF CREWS WERE CLRED TO THE PROFILE DSCNT PERIOD. THIS WAY; NO 'CONDITIONED' RESPONSE WOULD COME FROM THE CREW OTHER THAN SEARCHING IN THE CHART FOR THE APPROPRIATE ALTS. I DON'T SEE THE NEED FOR THE USE OF AN ALT WHEN CLRING A FLT FOR THE PROFILE SINCE ANY ALTS; OTHER THAN THE ONES DEPICTED ON THE CHART; WOULD MEAN YOU ARE NOT ON THE PROFILE DSCNT. I'VE DONE THIS ARR SEVERAL TIMES WITH NO PROBS; THE DAY IN QUESTION HAD BEEN A LONG DAY; PLAGUED WITH DEMANDING APCHS WITH LOW LEVEL WINDSHEAR AT EVERY ARPT WE HAD BEEN. TIREDNESS MAY HAVE ALSO PLAYED A ROLE IN THIS EVENT.