B737 FLC CONCERNED ABOUT PROX OF HELI TO THEIR FLT PATH DURING FINAL APCH.

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ON FINAL APCH TO MSY RWY 10; AT ABOUT 400 FT AGL; I OBSERVED A HELI CO-ALT; 90 DEGS TO OUR FLT PATH (POINTED TOWARD OUR FINAL). WE HAD SWITCHED TO TWR FREQ AT 12.5 MI; AND SINCE THAT TIME HAD NOT HEARD ANY XMISSION FROM THE HELI; NOR HAD TWR ADVISED US OF ITS PRESENCE. AS THE PNF; IT WAS EXTREMELY DISTRACTING TO HAVE AN ACFT IN THAT POS AND MONITOR THE APCH. AS THE HELI APCH 500 FT OFFSET; STILL PERPENDICULAR TO OUR FLT PATH; IT BEGAN A TURN TO FINAL THAT PARALLELED OUR FLT PATH; OFFSET 400 FT S. AT ABOUT 200 FT AGL WE PASSED THE HELI AND MADE OUR LNDG. IN RETROSPECT; A GAR WOULD PROBABLY HAVE BEEN APPROPRIATE; AS I MADE AN ASSUMPTION THAT THE HELI WOULD TURN FINAL AND LAND. THE OUTCOME OF THIS EVENT COULD HAVE BEEN VERY DIFFERENT IF EITHER PF WAS NOT ACTUALLY AWARE OF THE OTHER ACFT. THE CAPT CALLED TWR TO INDICATE OUR DISLIKE OF WHAT HAD JUST OCCURRED. LCL APOLOGIZED FOR NO CALL; BUT THEN SAID THAT THE HELI'S APCH WAS 'TYPICAL.' IT MAY BE THAT; BUT I WOULD SUBMIT THAT IT'S AN ACCIDENT WAITING TO HAPPEN.