ACR FLC INSTRUCTED TO EXECUTE A MISSED APCH WHEN ADVISING ATC THEY COULD NOT SIGHT DC9 AHEAD ON FINAL. THE FLC EXECUTE A FULL MISSED APCH WHEN UNABLE TO CLARIFY FREQ; AND ARE QUESTIONED BY DEP CTL WHY THEY WERE NOT ON RWY HDG. FO CONCERNED WITH TFC SPACING AND FREQ CONGESTION WHICH DELAYED HIS FLT.

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APCH CTL VECTORED US ON A BASE LEG AT 180 KIAS APPROX 2 1/2 MI BEHIND A DC9 FOR THE LOC RWY 31 AT LGA. WE WERE THEN GIVEN A VECTOR TO INTERCEPT THE FINAL; CLRED THE LOC RWY 31; AND TOLD TO CONTACT TWR. UPON CHKING IN WITH TWR; WE WERE ASKED IF WE HAD THE DC9 IN FRONT OF US IN SIGHT. THOUGH WE HAD THE ACFT ON THE TCASII; WE HAD LOST VISUAL CONTACT WITH THE DC9; AS HE BLENDED IN WITH THE GND LIGHTS. WE NOTIFIED TWR WE DID NOT HAVE A VISUAL WITH THE DC9. TWR DIRECTED US TO GO AROUND. WE INITIATED THE GAR AND CLBED TO 2000 FT MSL AS DIRECTED BY TWR AND SWITCHED TO APCH CTL. DUE TO THE SHORT CLB FROM 1600 FT TO 2000 FT WITH THE CHANGE IN THE GEAR AND FLAP CONFIGN AND A FREQ CHANGE; THE FREQ CHANGE TO APCH WAS DELAYED. IN FACT; AFTER REALIZING I ENTERED THE FREQ CHANGE INCORRECTLY; I HAD TO RETURN TO TWR TO CONFIRM THE PROPER FREQ. DUE TO RADIO SATURATION; I WAS UNACCEPTABLY DELAYED IN REACQUIRING THE FREQ. IN THE MEANTIME; THE CAPT WAS EXECUTING THE PUBLISHED MISSED APCH WHICH REQUIRED A CLBING R TURN TO THE ORCHY NDB. WHEN I FINALLY GOT HOLD OF APCH CTL; THEY WANTED TO KNOW WHY WE WERE TURNING TO ORCHY. I TOLD THE CTLR WE WERE CLRED THE LOC 31 AND WHEN TOLD TO GO AROUND; EXECUTED THE MISSED APCH PROC. THE CTLR WANTED TO KNOW WHAT INSTRUCTIONS TWR HAD GIVEN US ON THE GAR. BOTH THE CAPT AND I HEARD 'GO AROUND; CLB TO 2000 FT; CONTACT APCH CTL.' NEVER DID WE HEAR (OR RECALL HEARING) 'MAINTAIN RWY HDG.' DUE TO THE DELAY IN CONTACTING APCH CTL; WE FLEW THE PUBLISHED MISSED APCH. (HE ACTUALLY EXPECTED US TO FLY RWY HDG.) THE SIT COULD HAVE BEEN AVOIDED IF APCH CTL HADN'T ORIGINALLY PUT US IN SO TIGHT ON THE DC9 (2 1/2 MI). OBVIOUSLY; THE UNANTICIPATED GAR COMMAND; TASK SATURATION ASSOCIATED WITH THE GAR WITH ONLY A SHORT CLB OF 400 FT; AND A FREQ CHANGE LED TO THE DELAY IN CONTACTING APCH. THIS IS A SIT THAT COULD BE REPEATED AGAIN IN THE FUTURE. I THINK THE BEST WAY TO REDUCE THAT LIKELIHOOD IS TO QUIT TRYING TO CRAM TOO MANY AIRPLANES INTO CONFINED AIRSPACE. MORE SPACING WOULD HAVE PREVENTED THE GAR IN THE FIRST PLACE.