Narrative:

Approximately 50 mi south of jac, slc center informed us that another aircraft was shooting a practice ILS approach to runway 18 at jac, and asked us to slow down to avoid holding. We slowed and changed our request from VOR-DME 36 with a visual 18 to the ILS runway 18 to avoid a delay. We were cleared direct dunior for the ILS nopt to runway 18. Prior to dunior, center gave holding instructions for quirt with an expected further clearance of XA15Z. Shortly thereafter, the other aircraft, a light twin, canceled IFR, and went to advisory frequency and left center's radar coverage of 13000 ft MSL. Center then cancelled our holding and cleared us to intercept the ILS to runway 18, and said 'cleared the ILS approach runway 18.' at this time, we did not have the preceding aircraft in sight or the runway in sight. We continued on the approach. After being handed to tower, we asked where the other aircraft was, and discovered that the pilot had not spoken to tower yet. Tower had no idea where he was. At 10 mi on final, we received a yellow TCASII advisory that the light twin was .1 NM behind, and 700 ft below. At this time, we were descending rapidly to catch up. We initiated a go around and landed uneventfully. After much discussion, the captain and I decided everything was done by the book, but more could have been done by the controller to relieve a possible conflict.

Related reports:

Google
 

Original NASA ASRS Text

Title: B757 LNDG JAC EXPERIENCED GAR BECAUSE OF UNKNOWN TFC AND EXCESS ALT.

Narrative: APPROX 50 MI S OF JAC, SLC CTR INFORMED US THAT ANOTHER ACFT WAS SHOOTING A PRACTICE ILS APCH TO RWY 18 AT JAC, AND ASKED US TO SLOW DOWN TO AVOID HOLDING. WE SLOWED AND CHANGED OUR REQUEST FROM VOR-DME 36 WITH A VISUAL 18 TO THE ILS RWY 18 TO AVOID A DELAY. WE WERE CLRED DIRECT DUNIOR FOR THE ILS NOPT TO RWY 18. PRIOR TO DUNIOR, CTR GAVE HOLDING INSTRUCTIONS FOR QUIRT WITH AN EXPECTED FURTHER CLRNC OF XA15Z. SHORTLY THEREAFTER, THE OTHER ACFT, A LIGHT TWIN, CANCELED IFR, AND WENT TO ADVISORY FREQ AND LEFT CTR'S RADAR COVERAGE OF 13000 FT MSL. CTR THEN CANCELLED OUR HOLDING AND CLRED US TO INTERCEPT THE ILS TO RWY 18, AND SAID 'CLRED THE ILS APCH RWY 18.' AT THIS TIME, WE DID NOT HAVE THE PRECEDING ACFT IN SIGHT OR THE RWY IN SIGHT. WE CONTINUED ON THE APCH. AFTER BEING HANDED TO TWR, WE ASKED WHERE THE OTHER ACFT WAS, AND DISCOVERED THAT THE PLT HAD NOT SPOKEN TO TWR YET. TWR HAD NO IDEA WHERE HE WAS. AT 10 MI ON FINAL, WE RECEIVED A YELLOW TCASII ADVISORY THAT THE LIGHT TWIN WAS .1 NM BEHIND, AND 700 FT BELOW. AT THIS TIME, WE WERE DSNDING RAPIDLY TO CATCH UP. WE INITIATED A GAR AND LANDED UNEVENTFULLY. AFTER MUCH DISCUSSION, THE CAPT AND I DECIDED EVERYTHING WAS DONE BY THE BOOK, BUT MORE COULD HAVE BEEN DONE BY THE CTLR TO RELIEVE A POSSIBLE CONFLICT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.