N58318 (HUGHES 369, UNDER CONTRACT WITH US GEOLOGICAL SURVEY) WAS INBND FM SE TO LND AT KETCHIKAN-TEMSCO HELIPORT (6Z4) AS N73WS (CESSNA 185 AMPHIBIAN) WAS DEPG SE FM KETCHIKAN INTL ARPT (KTN). KTN & 6Z4 WERE LOCATED IN TONGASS NARROWS WITHMTNS NE & SW. RPRTD WX WAS: 500' SCT, 1100' BKN, 2200' OVC, VIS 5 MI WITH LGT RAIN & FOG, CIG RAGGED. FOR A VFR APCH TO 6Z4 (APRX 1-1/2 MI NORTH OF KTN ARPT), N58318 HAD TO GO UP THE NARROWS & OVR OR NR KTN. KTN HAD NO CTL TWR, BUT SUB- PART M OF FAR 93 REQD 2-WAY RDO COMM WITH KTN FSS, WHILE OPERG BLO 3000' & W/I 3 MI OF KTN. AT 1318:58, N58318 RPRTD AT GRAVINA PT (APRX 4 MI SE OF KTN) & THE FSS PROVIDED TRAFFIC ADZR. AT 1319:19, N73WS RPRTD INTENTIONS TO DEPART FROM KTN & WAS GIVEN A TRAFFIC ADZY, INCLUDING INFO CONCERNING N58318. N73WS DEPD KTN, USING PARALLEL TWY NEXT TO RWY 11, IAW LTROF AGREEMENT. NRLY 1 MI SE OF KTN, THE TWO COLLIDED AS N58318 WAS FLYING NEAR THE EXTDD CNTRLN OF RWY 11. N58318 CRASHEDIN WTR; N73WS RETURNED & CRASH LNDD AT KTN. FIVE ACFT IN VCNTY OF KTN; FAA DATA INDCD HVY TRAFFIC AT KTN FM MAY TO SEP.