FO OF A B757 WAS SLOW IN STARTING DSCNT FOR A XING RESTR RESULTING IN UNDERSHOOTING RESTR.

Narrative

WE HAD INITIATED OUR DSCNT INTO THE CHICAGO AREA ON A CLR NIGHT. WE WERE GIVEN A XING RESTR TO BE AT FL240 30 MI W OF JOLIET; IL. I WAS CALLING IN-RANGE TO OUR COMPANY OPS WHEN THE CALL FROM ATC CAME. I OVERHEARD THE FO REPEAT THE INSTRUCTIONS BUT CONTINUED TO TALK TO THE COMPANY FOR APPROX 1 MORE MIN. WHEN I RETURNED TO THE ATC FREQ; THE FO HAD INITIATED THE DSCNT; BUT WAS A LITTLE HIGH ON THE PROFILE; BECAUSE THE RESTR WAS GIVEN AT SUCH A LATE TIME. I DEPLOYED THE SPOILERS AND IT APPEARED THAT THE RESTR WOULD BE MADE. I WAS USING THE FIX PAGE ON THE FMC TO DETERMINE OUR DISTANCE TO JOLIET. AS 31 DME OR 1 MI TO OUR RESTR WE WERE AT 25000 FT WITH A VVI OF ABOUT 2500 FPM; WHEN THE CTLR ASKED US OUR ALT BECAUSE WE WERE PASSING THE XING RESTR. I LOOKED DOWN AND TOLD HIM WE WERE NOW PASSING 24400 FT. HE DID NOT RESPOND AND TOLD US TO CONTACT A NEW FREQ. ACCORDING TO THE FMC THE RESTR WAS MADE. I DO NOT KNOW IF A VIOLATION DID INDEED OCCUR. A NUMBER OF ACTIONS COULD HAVE ALLEVIATED THE PROB. AN EARLIER DSCNT FROM THE CTLR; AND AN EARLIER INITIAL DSCNT FROM THE CREW. I COULD HAVE ALSO CALLED UP RAW DATA TO BACK UP THE FMC IF IN FACT THE IRU'S WERE GIVING ME INCORRECT INFO. I ALSO COULD HAVE NOTIFIED THE CTLR THAT IT WOULD BE CLOSE AND ASK FOR SOME RELIEF. IN ADDITION; IF THE COMPANY HAD ACARS I WOULD NOT HAVE HAD TO BE OUT OF THE LOOP ON A DIFFERENT FREQ. CREW FATIGUE COULD HAVE ALSO FACTORED INTO THE SIT SINCE THE FO HAD DEADHEADED OUT TO SAN FRANCISCO ON THE SAME DAY AND THEN WORKED THE FLT RIGHT BACK (OVER 8 HRS 30 MINS).