POTENTIAL CONFLICT WITH LTSS BTWN 2 ACR ACFT; BOTH ON VISUAL APCHS AND CLRED TO LAND ON THE SAME RWY. NO INDICATION FROM TWR SO FAR AS WHO WAS #1 OR WHO WAS THE SUCCEEDING ACFT.

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ON FLT FROM DENVER TO GRAND JUNCTION ON AUG/FRI/91; WE HAD A NEAR MIDAIR WITH AN ACR COMMUTER LTT WHILE ON A VISUAL APCH TO RWY 11. AN FAA INSPECTOR WAS PERFORMING A SAFETY INSPECTION FROM THE JUMP SEAT. WE WERE ON A L DOWNWIND TO RWY 11 WHEN THE TWR CTLR CLRED US TO LAND. TURNING L BASE THE TWR ADVISED US OF VFR TFC ON A 10 MI FINAL TO 11. WE CALLED NEGATIVE CONTACT AND RECONFIRMED OUR CLRNC TO LAND. DURING MY TURN TO FINAL (5-6 MI FROM THE THRESHOLD) THE FAA INSPECTOR CALLED OUT THE LTT TFC AT OUR 12:30 POS AND JUST BELOW US. I ESTIMATE THE SEPARATION WAS 500 FT VERTICALLY AND LESS THAN 1 MI. UPON ACQUIRING THE LTT VISUALLY I IMMEDIATELY STOPPED MY L TURN AND DSCNT; ROLLING INTO A 30 DEG BANK TO THE R IN ORDER TO AVOID A COLLISION. AFTER WE TOOK EVASIVE ACTION THE TWR ASKED US TO 'EXTEND OUR BASE'. WE MADE A R 360 DEG TO REALIGN ON FINAL AS THE LTT LANDED IN FRONT OF US. VISIBILITY WAS VERY GOOD (20-30 MI). THE TWR HAD CLRED BOTH AIRPLANES TO LAND ON THE SAME RWY AT THE SAME TIME AND FAILED TO GIVE US SEPARATION WHEN WELL WITHIN HIS SIGHT. FORTUNATELY FOR US THE FAA INSPECTOR SAW THE TFC FROM HIS ELEVATED POS LOOKING DOWN OVER OUR SHOULDERS. HE GAVE US THE EXTRA SECONDS WE NEEDED TO AVOID A COLLISION. HE ALSO SAID THAT HE WAS GOING TO PULL THE ATC TAPES FOR THE INVESTIGATION. EVEN THOUGH IT WAS A NON RADAR ENVIRONMENT; THE CTLR FAILED IN HIS DUTY TO SEPARATE TFC CLOSE TO THE RWY. OTHER CREWS HAVE COMPLAINED OF SIMILAR INCIDENTS IN GRAND JUNCTION. IT'S ONLY A MATTER OF TIME (OUR MLG WAS NON TCASII).