CAPT OF AN ATX DASSAULT FALCON; DA20; TOOK OFF BELOW MINIMUM RVR REQUIRED FOR HIS PART 135 OPS SPECS. REDUCED VISIBILITY TKOFS ARE PERMITTED PROVIDING THAT THERE ARE 3 RVR RPTING POINTS. THIS ARPT ONLY HAD THE ONE LOCATED AT THE DEP END.

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MY COMPANY DISPATCH TOLD ME THE VISIBILITY AT THE ARPT WAS 2 1/4 MI; WHEN THEY NOTIFIED ME OF THE TRIP. I KNEW IT HAD BEEN FOGGY THAT NIGHT. UPON MY ARR AT THE ARPT; THE VISIBILITY HAD DROPPED TO 1/4 MI; FOG. WHEN I STARTED MY TAXI; GND CTL HAD ADVISED US THAT RWY 5 RVR WAS 1200 FT. WE SWITCHED TO TWR AND WERE CLRED FOR POS AND HOLD ON RWY 5. TWR THEN CALLED 'RVR 1000 FT CLRED FOR TKOF.' OUR COMPANY'S PART 135 OPS SPECS ALLOW REDUCED VISIBILITY TKOFS DOWN TO 600 FT RVR. HOWEVER; FOR TKOF VISIBILITY LESS THAN 1/4 MI OR 1200 RVR THE RWY MUST BE EQUIPPED WITH 3 SEPARATE RVR MEASURING DEVICES. ADDITIONALLY; 2 OUT OF 3 MUST BE WORKING AND ALL RPTING 600 FT VISIBILITY OR MORE. MY DECISION TO TKOF COMPROMISED SAFETY. I LATER FOUND OUT THAT THIS RWY WAS EQUIPPED WITH RVR AT THE TOUCHDOWN AREA ONLY. NO RVR WAS AVAILABLE FOR MIDFIELD OR END OF RWY VISIBILITY. AS CAPT; I AM RESPONSIBLE TO KNOW THE MORE DIFFICULT REGULATIONS LIKE THIS ONE. NEXT TIME I'LL MAKE A RADIO CALL TO FIND OUT WHICH VISIBILITY IS BEING RPTED. A CALL TO THE CTL TWR WOULD HAVE CLRED UP ANY CONFUSION REGARDING WHICH VISIBILITY WAS BEING RPTED. I FOUND THIS INFO (ARPT RVR EQUIP) DIFFICULT TO FIND IN ARPT INFO PUBS. I FINALLY PHONED THE CTL TWR TO FIND OUT FOR MYSELF. THE REST OF THE FLT WAS UNEVENTFUL.