THE PIC OF A CL65 QUESTIONS THE ILLUSION HE FELT WHEN USING THE NEW; TEMPORARY PAPI INSTALLED FOR THE DISPLACED THRESHOLD ON RWY 36L AT CVG.

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APCHING CVG FROM THE SW; ATC HAD VECTORED US ONTO A HIGH L DOGLEG TO FINAL FOR THE RWY 36L VISUAL APCH. ACCORDING TO THE NOTAMS ON OUR DISPATCH THAT PORTION OF RWY 36L S OF TXWY K WAS CLOSED LEAVING 6400 FT AVAILABLE FOR TKOF AND LNDG. AS WE TURNED FINAL; I ATTEMPTED TO FLY WHAT I BELIEVED TO BE A 3 DEG GLIDE PATH TO THE RELOCATED THRESHOLD. HOWEVER; I SPOTTED A PAPI DOWN THE RWY ON THE L SIDE NEAR THE RELOCATED THRESHOLD AND IT INDICATED THAT I WAS BELOW THE GLIDE PATH. I REDUCED OUR RATE OF DSCNT AND ASKED MY FO IF SHE KNEW ANYTHING ABOUT A NEW PAPI INSTALLATION. SHE SAID THAT ACCORDING TO THE ATIS THERE WAS A NEW PAPI; BUT IT WAS NOT IN SVC. (I THOUGHT IT WAS RATHER PECULIAR TO HAVE THE PAPI ON; BUT CALL IT OTS. BUT THIS WAS NOT WITHOUT PRECEDENT. YRS AGO FLT INSTRUCTING AT DAY; THE RWY 24L VASI WAS NOTAMED OTS BUT WAS STILL ON. AND IN NASSAU (MYNN) THE PAPI'S BURN BRIGHT BUT HAVE BEEN LABELED 'ON TEST ONLY' FOR YRS.) SO; WE LEVELED OFF AND THE ONE THING I WANTED TO BE SURE OF WAS XING THE RELOCATED THRESHOLD AT OR ABOVE 50 FT AGL. THE AIRPLANE CALLED OUT '50' AND THE RELOCATED THRESHOLD SLID UNDER THE NOSE. THE LNDG WAS UNEVENTFUL AND ATC MADE NO COMPLAINTS. THE WHOLE PAPI-QUESTIONING PROCESS LASTED ONLY ABOUT 20 SECONDS. I USUALLY LISTEN IN WHEN THE FO GETS THE ATIS; BUT THIS TIME I DIDN'T. AND THE FO APPARENTLY MISUNDERSTOOD WHAT WAS SAID BECAUSE WHEN I CALLED ABOUT THE PAPI VIA ATIS LATER THAT DAY; THE ATIS SAID THE PAPI WAS IN SVC ON RWY 36L. I WAS UNABLE TO LEARN WHETHER THE GLIDE ANGLE IS A STANDARD 3 DEGS OR STEEPER. BUT WHEN I FOLLOWED THE PAPI THE NEXT MORNING; THE ON-GLIDE PATH ANGLE LOOKED VERY STEEP. IF THIS WAS AN OPTICAL ILLUSION CAUSED BY THE LENGTHY THRESHOLD RELOCATION; THEN IT WAS A VERY PWRFUL ILLUSION; INDEED. HAD I HEARD '50' ANY SOONER; WE WOULD HAVE GONE AROUND.