Narrative:

I descended to a cruise altitude of 9500' on a heading of 175 degrees. The aircraft did not have mode C transponder, so I was flying below the maximum altitude until I could cross the mountains at teton pass southwest of jac. I was approximately 5 mi east and 5 mi north of jac when an airliner called jac radio on 122.8 to announce he was 10 mi south of the airport and landing. An small aircraft Y behind me called and said he was 5 mi north of the airport cruising at 11000'. I called jac radio and announced my position and altitude. Jac radio called back a few seconds later to ask my position again. I was in the process of restating my position (I was almost abeam the #'south on the north end of the runway and about 5 mi to the east) when the airliner passed almost directly under me on an almost completely opp heading. I never saw the descending airliner until he was almost directly under me and I had no time react. I then told jac radio that the airliner passed below me, as did the fellow in the small aircraft Y. I monitored the frequency until I crossed teton pass, and did not hear any comment from the airliner crew as to whether or not they ever saw me. I don't think airliners on IFR flight plans controled out of slc should be coming inot a unicom airport with clearance to land when slc cannot discern who is in the air.

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Original NASA ASRS Text

Title: CLOSE PROX ACR-MLG GA-SMA 5 NM EAST OF JAC.

Narrative: I DSNDED TO A CRUISE ALT OF 9500' ON A HDG OF 175 DEGS. THE ACFT DID NOT HAVE MODE C XPONDER, SO I WAS FLYING BELOW THE MAX ALT UNTIL I COULD CROSS THE MOUNTAINS AT TETON PASS SW OF JAC. I WAS APPROX 5 MI E AND 5 MI N OF JAC WHEN AN AIRLINER CALLED JAC RADIO ON 122.8 TO ANNOUNCE HE WAS 10 MI S OF THE ARPT AND LNDG. AN SMA Y BEHIND ME CALLED AND SAID HE WAS 5 MI N OF THE ARPT CRUISING AT 11000'. I CALLED JAC RADIO AND ANNOUNCED MY POS AND ALT. JAC RADIO CALLED BACK A FEW SECS LATER TO ASK MY POS AGAIN. I WAS IN THE PROCESS OF RESTATING MY POS (I WAS ALMOST ABEAM THE #'S ON THE N END OF THE RWY AND ABOUT 5 MI TO THE E) WHEN THE AIRLINER PASSED ALMOST DIRECTLY UNDER ME ON AN ALMOST COMPLETELY OPP HDG. I NEVER SAW THE DSNDING AIRLINER UNTIL HE WAS ALMOST DIRECTLY UNDER ME AND I HAD NO TIME REACT. I THEN TOLD JAC RADIO THAT THE AIRLINER PASSED BELOW ME, AS DID THE FELLOW IN THE SMA Y. I MONITORED THE FREQ UNTIL I CROSSED TETON PASS, AND DID NOT HEAR ANY COMMENT FROM THE AIRLINER CREW AS TO WHETHER OR NOT THEY EVER SAW ME. I DON'T THINK AIRLINERS ON IFR FLT PLANS CTLED OUT OF SLC SHOULD BE COMING INOT A UNICOM ARPT WITH CLRNC TO LAND WHEN SLC CANNOT DISCERN WHO IS IN THE AIR.

Data retrieved from NASA's ASRS site as of August 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.