Widebody; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Confusion
ATC Issue All Types; Conflict Airborne Conflict
Aircraft; Procedure
Over ONOHI on the VECKI 7 arrival to KOA we were cleared for the ILS 17 by HCF.  We were descending through about 12;000 feet when HCF notified us that there was traffic at 11 o'clock opposite direction at 8;500 feet.  We searched visually and were not able to pick up Aircraft right away.  We then heard HCF suggest a 20 degree turn to the right [of] Aircraft Y.  Passing through about 11;000 feet we picked it up on TCAS and saw that it was at 11:30 and heading almost straight at us at 8;500 feet.  We were in VNAV with the autopilot on and so our airplane leveled to slow to 240 just prior to reaching 10;000 feet.  I think that if we had not decreased our descent rate to slow that we would have gotten an RA and would have had to change our path.  Passing through 10;000 feet we visually acquired Aircraft Y passing off to our left about 1;500 feet below us. We were cleared for the ILS to 17 and were descending on the arrival at the time of the traffic advisory from HCF.  How are [these aircraft] allowed to depart basically straight up the localizer course when there is traffic cleared for the ILS?Departing traffic should be prohibited from flying right up the localizer course.  Ours turned out to be a non-event; but relying on us to see each other is dangerous; especially when we are descending right through their altitude on the approach.
Pilot inbound to KOA describes conflict with another aircraft that is flying the back course of the ILS he is flying.