B737 AND FLT OF FIVE HELO'S HAD LESS THEN LEGAL SPACING IN GASTINEAU CHANNEL WHILE FLYING THE RWY 26 R-NAV APCH TO JNU.

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WE WERE FLYING THE RNAV RWY 26 APPROACH TO JUNEAU. AT MARNM WE RPTED OUR POS AND INTENTIONS TO VFR TFC ON FREQ 123.05. WE ALSO WERE TOLD TO RPT 'TRAWL' BY JUNEAU TWR (118.7) FOR LNDG CLRNC. AFTER WE MADE OUR RPT ON THE COMMON TFC FREQ (123.05) WE HEARD A RPT FROM A FLT OF FIVE HELO'S THAT INTENDED TO CROSS THE GASTINEAU CHANNEL AT 2000 FT OVER THE CITY OF JUNEAU. I ESTIMATED THAT WE WOULD BE CLOSE TO THAT ALTITUDE ABEAM JUNEAU AND MADE AN ANNOUNCEMENT OF 123.05 TO THAT EFFECT. I RECEIVED NO RESPONSE. ALTHOUGH RPTED WX AT THE JUNEAU ARPT WAS APPROX 3400 FT BROKEN WITH GOOD VISIBILITY; WE WERE IMC UNTIL ABOUT 1800 FT TO 2000 FT WE PICKED UP THE HELO'S ON TCAS AND WE CONCERNED THAT THEY WERE NEAR OUR ALTITUDE. AS WE 'BROKE OUT' OF THE CLOUDS VISIBILITY WAS RESTRICTED AT TIMES BY RAIN AND MIST. I PICKED UP THE 1ST HELO VISUALLY ABOVE US AND STARTED TO ACQUIRE THE IN-TRAIL HELO'S CLIMBING ACROSS OUR PATH. AS I HAD GND CONTACT I DIRECTED THE PLT FLYING TO DISENGAGE THE AUTOPILOT AND DESCEND. AT THE SAME TIME WE RECEIVED A COUPLE 'TA'S' AND THEN AN 'RA' TO DESCEND. THE HELICOPTERS APPEARED TO BE JUST BELOW THE RAGGED OVERCAST WITH IN TRAIL BIRDS CLIMBING TO 2000 FT ACROSS OUR PATH. PROC'S NEED TO BE RE-ESTABLISHED AND RE-ENFORCED REGARDING DECONFLICTING IFR AND VFR TFC IN THIS NARROW CORRIDOR (GASINEAU CHANNEL). ANNOUNCEMENTS ON A FREQ IS NOT ENOUGH. THE HELICOPTERS WERE PROBABLY FOLLOWING NOISE ABATEMENT PROCEDURES WHICH CONFLICT WITH OUR INSTRUMENT APPROACHES AND DEPARTURES INTO JUNEAU. THE SURROUNDING TERRAIN MAKES MANEUVERING VERY DIFFICULT IN A SIT LIKE THIS AND IT'S A NON-RADAR ENVIRONMENT. THE TCAS SYSTEM WAS CERTAINLY A MAJOR FACTOR IN OUR SITUATIONAL AWARENESS AND AVOIDANCE OF A SIGNIFICANT NEAR OR ACTUAL MID-AIR THREAT.