ACR MLG FAILS TO MAKE ALT XING RESTRICTION AFTER AMENDED CLRNC ALT CHANGE GIVEN IN DSCNT PROC.

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RTE OF FLT INCLUDED THE MILTON 7 ARR INTO LGA. WE WERE CLRED FROM FL370 TO FL250 W OF MIP IN TIME TO MAKE ALL ALT RESTRICTIONS ON THE ARR. A SLOW DSCNT WAS INITIATED SINCE THE CLRNC WAS EARLY. (CHANGED CRUISE ALT IN FMC.) APCHING APPROX 50 MI FROM MARRC WHEN WE INTENDED TO INCREASE OUR RATE OF DSCNT; OUR ALT CLRNC WAS CHANGED TO FL290. WE CONTINUED THE SLOW RATE OF DSCNT SINCE WE WERE RESTR TO FL290. APPROX 20-23 MI W OF MARRC AND DSNDING THROUGH FL310 THE CTLR GAVE CROSS MARRC AT FL180. IMMEDIATELY AN IDLE PWR; SPD BRAKES EXTENDED AND AN INCREASED AIRSPD DSCNT WAS INITIATED. THE COMPUTER DSCNT LINE INDICATED WE COULD NOT MAKE THE RESTRICTION SO I NOTIFIED ZNY WHEN WE WERE DSNDING THROUGH FL280 AND APPROX 18 MI W OF MARRC; THAT WE COULD NOT MAKE THE RESTRICTION. HE SAID WE SHOULD HAVE DSNDED FASTER EARLIER IN THE DSCNT AND I REPLIED WE COULD NOT HAVE MADE IT DUE TO THE FL290 ALT WE WERE ASSIGNED. HE GAVE US ANEW XING '10 MI E OF MARRC AT FL180' WHICH WE WERE BARELY ABLE TO MAKE. THE WINDS THAT NIGHT WERE 124 KTS FROM 270 DEGS WHICH MADE THINGS DIFFICULT. THE CTLR HAD NOT MENTIONED AN 'EXPECT FL180 AT MARRC.' IT IS WRITTEN ON THE ARR BUT WHEN RESTR TO FL290 WE DOUBTED THAT WE WERE GOING TO GET IT SINCE WE WERE GETTING TOO CLOSE TO MAKE IT. EVEN IF WE HAD BEEN AT FL290.