A B757 CREW ON THE LGA KORRY 3 STAR DSNDED BELOW THEIR CLRED ALT WHEN TASK SATURATED WITH HOLDING INSTRUCTIONS AND DSCNT CLRNC.

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I WAS THE PLT MONITORING ON A FLT TO LGA. WE WERE INBOUND ON THE KORRY 3 ARR AND BEGAN TO RECEIVE NUMEROUS CLRNCS TO CHANGE THE ARR IN ONE WAY OR ANOTHER. AFTER PASSING ENO WE WERE GIVEN THE ATC CLRNC TO 'DSND VIA THE KORRY ARR AND TO ALSO CROSS SKIPY AT OR BELOW FL220.' THE FO INITIALLY SELECTED FLT LEVEL CHANGE TO EXPEDITE OUR DSCNT TO GET BELOW FL220 WHILE HE INPUTTED THIS CHANGE TO THE ARR; AND AFTER WE DSNDED BELOW FL220 HE WENT BACK TO VNAV. WE COMPLIED WITH ALL OF THESE CLRNCS. A SHORT TIME AFTER THIS WE WERE GIVEN ANTHER CLRNC TO CROSS BRAND AT 250 KTS. MY FO MADE THE NECESSARY INPUT TO THE FMS. THE ATC CTLR INFORMED US HE WOULD HAVE HOLDING INSTRUCTIONS IN A MOMENT. SOMETIME AROUND THE TIME OF ISSUING HOLDING INSTRUCTIONS AT RBV TO US; HE ALSO RESTATED THE CLRNC TO DSND VIA THE KORRY ARR; HOWEVER; TO NOW CROSS BRAND AT 11000 FT. THE PRINTED ARR HAS BRAND LISTED AT 11000 FT OR ABOVE. I REMEMBER CHKING TO SEE THAT MY FO HAD CORRECTLY CHANGED THE FMS TO REFLECT THAT WE NOW NEEDED TO CROSS BRAND AT 250 KTS AND AT 11000 FT. THE FMS REFLECTED THIS AND I REMEMBER THAT OUR ALT SELECT WINDOW ON THE MCP REFLECTED 10000 FT AS THAT WAS THE FINAL ALT ON THE ARR. I HAD MONITORED THE XING OF ALL OF THE PREVIOUS FIXES AND WAS BUSY CHKING THE ARR PAGE TO VERIFY THAT WE HAD ALSO CORRECTLY ENTERED THE HOLDING INFO AT RBV WHEN WE RECEIVED A CLRNC TO CLB TO 11000 FT AS THERE WAS AN ACFT HOLDING AT 10000 FT. WE WERE JUST PASSING 10600 FT AND MY FO IMMEDIATELY SELECTED VERT SPD AND ROLLED IN A CLB OF 1500 FPM. I QUERIED THE CTLR TO VERIFY THAT WE WERE CLRED TO 'DSND VIA THE KORRY ARR;' AND HE RESPONDED THAT WE WERE BUT WE WERE TO CROSS BRAND AT 11000 FT. SINCE I WAS BUSY XCHKING THE HOLDING INFO ON THE ARR PLATE; BRAND WAS THE ONE FIX THAT I DID NOT ACTUALLY VERIFY THE PASSING OF AS WE WERE DOING IT. THE SEEMINGLY CONTINUAL CHANGES THAT WERE GIVEN TO US FOR THE KORRY ARR CAUSED A SIGNIFICANT AMOUNT OF CONFUSION; INTO WHAT IS ALREADY A VERY BUSY STAR. IF THE CTLR'S REAL INTENT WAS FOR US TO NEVER DSND BELOW 11000 FT; THEN THAT CLRNC WAS NEVER RECEIVED OR ACKNOWLEDGED BY US. IF HE WANTED US TO CROSS BRAND AT 11000 FT AND THEN DSND TO 10000 FT; I HAVE TO BELIEVE THAT WE COMPLIED WITH THAT AS I HAD PREVIOUSLY SEEN THAT CLRNC LOADED INTO THE LEGS PAGE OF THE FMS. HOWEVER; I CANNOT BE 100% SURE AS I DID NOT VISUALLY CONFIRM THE PASSING OF THAT PARTICULAR FIX AS I WAS CHKING THE ARR PLATE TO SEE THAT THE HOLDING INSTRUCTIONS WERE ALSO CORRECTLY IN THE FMS. I THINK IT WOULD HELP TO EITHER HAVE THE CLRNC TO DSND VIA OR TO BE GIVEN REGULAR ATC CLRNCS TO DSND. USING A COMBINATION OF THE TWO ALONG WITH HOLDING INSTRUCTIONS IS POTENTIALLY CREATING A SITUATION FOR MISCOM OR CONFUSION; AND MOST DEFINITELY ADDING A GREAT DEAL TO THE PLT'S WORKLOAD.