UNAUTH RWY OP WHEN MLG LANDS ON A RWY BUT CREW HAS NO PERFORMANCE DATA FOR THAT RWY.

Narrative

WE HAD PASSED THROUGH KTUL EARLIER THE SAME MORNING. SINCE PREVAILING WINDS WERE FROM THE S AT ABOUT 15 KTS WE HAD USED OUR USUAL RWY (18L) FOR LNDG. TO EXPEDITE OPS; WE HAD USED RWY 26 FOR DEP. UPON RETURNING TO KTUL; ATIS ADVISED THAT RWY 18L WAS CLOSED AND THAT THE TUL VORTAC WAS STILL OTS. SINCE THE VORTAC WAS OTS; VECTORS TO THE ILS 18R WERE BEING USED TO PROVIDE POSITIONING FOR LET- DOWNS. CEILINGS WERE RAGGED AT THE 2500 FT AGL LEVEL AND VISIBILITY WAS GREATER THAN 10 MI. WE WERE VECTORED TO THE FINAL APCH FIX (KROAK INTXN FOR RWY 18R) AT 2500 FT MSL. WITH THE ARPT IN SIGHT PRIOR TO REACHING THE FINAL APCH FIX; WE WERE CLRED FOR A VISUAL APCH TO RWY 18R; OTHER TFC WAS ON VECTORS TO RWY 26L SINCE I HAD NEVER LANDED ON RWY 18R IN ACR OPS; I CHKED THE ARPT DIAGRAM TO VERIFY ITS DIMENSIONS. I FOUND IT TO BE LARGER THAN 2 OTHER ARPTS WHICH WE REGULARLY SERVE. BEING SATISFIED THAT IT WAS MORE THAN ADEQUATE FOR OUR OP; I THOUGHT NO MORE ABOUT USING RWY 18R. WHILE CALCULATING DATA FOR DEP; WE FOUND THAT OUR PERFORMANCE MANUALS DID NOT HAVE DATA FOR TKOF OR FOR LNDG ON RWY 18R. FURTHER; I COULD NOT FIND ANY DATA LIMITING RWY 18R USAGE BECAUSE OF STRUCTURAL WT LIMITS. SINCE THE RWY IS LARGER THAN OTHERS (AT SIMILAR ELEVATIONS) WHICH WE REGULARLY USE; AND SINCE THE RWY IS NOT WT LIMITED; I BELIEVE OUR USE OF IT WAS SAFE; ALTHOUGH I DO NOT HAVE PERFORMANCE DATA TO SUPPORT THAT CONTENTION.