DSNDING FROM 15000 FT TO 9000 FT; BRIEFING FOR THE APCH; DSNDED TO 8500 FT.

Narrative

IT WAS OUR FIRST LEG OF THE SECOND DAY OF AN OVERNIGHT IN BUFFALO. THE FLT DEPARTED BUFFALO AT XA45 AM LCL FOR BGM. AT ABOUT XB12 WE RECEIVED A CLRNC TO DSND AT 'OUR DISCRETION' FROM 15000 FT TO 9000 FT. I BEGAN OUR DSCNT ABOUT 45 DME W OF BGM VOR. SOON WE WERE HANDED OFF TO BGM APCH. WE ACQUIRED ATIS AND BEGAN TO BRIEF FOR THE APCH. ILS RWY 16 BGM. WE RECEIVED A VECTOR FROM BGM APCH OF 100 DEGS. SUDDENLY I HEARD THE ALT ALERT GO OFF AND THE CAPT STATE 'CHK ALT 9000 FT.' CAPT THEN BEGAN TO PULL ON THE YOKE AND ADD PWR BECAUSE WE WERE DSNDING THROUGH 9000 FT. WE BOTTOMED OUT AT 8500 FT AND CLBED BACK UP IMMEDIATELY. BGM APCH CALLED 'MAINTAIN 9000 FT.' WE WERE ALREADY CLBING THROUGH 8700 FT WHEN WE HEARD THAT CALL. THE REST OF THE APCH WENT AS NORMAL AS PLANNED. I BELIEVE THE REASON THIS ALT EXCURSION OCCURRED IS BECAUSE I COMPLETELY FORGOT ABOUT THIS ALT RESTR OF 9000 FT. IT WAS EARLY; I WAS TIRED; WE WERE HIGH AND COMING DOWN FAST. BGM APCH HAS A HABIT ALONG WITH ZNY TO LEAVE US AT A HIGH INITIAL ALT FOR A LONG TIME; THEREFORE MY MINDSET WAS WE HAVE TO HURRY TO MAKE IT TO THE ILS INITIAL ALT. BY THE TIME I REALIZED I HAD FORGOTTEN TO STOP DSNDING AT 9000 FT WE WERE ALREADY AT 8800 FT. IT TOOK 300 FT MORE TO RECOVER FROM THE 1500-2000 FPM DSCNT. THE WHOLE EVENT OCCURRED IN LESS THAN 10 SECONDS. I TAKE COMPLETE RESPONSIBILITY FOR LOSING MOMENTARY SITUATIONAL AWARENESS.