Narrative:

Arrived at gsp airport at XA15 am for XB00 am departure after short overnight. Looked at WX and called company dispatch to get a takeoff alternate. This discussion took some time because most of the area airports had low visibility. Arrived at cockpit, first officer advised the RVR was 1200 ft and we needed at least 1600 ft to depart. We completed the preflight procedures and called for pushback clearance from gsp ground control. We were cleared to taxi and advised the RVR was 1600 ft. At the end of the runway RVR dropped to 800 ft. Several civilian aircraft took off, and reported tops at 50 ft AGL. Tower reported RVR improving to 1200/1400 ft, and cleared us for takeoff. After airborne I realized we needed 1600 ft RVR to depart. This was a confusion of 1200/1000 ft RVR with centerline operating but runway markings obscured by contaminants, by myself and the first officer. This runway is good for 600 ft RVR with centerline lights operating but they were OTS. We could see approximately 10 runway lights when we took the runway which would be about 2000 ft RVR. The takeoff was uneventful and we were out of the fog after rotation. Supplemental information from acn 297400: during preflight preparation ATIS reported RVR at 1000 ft. The runway in use has published takeoff mins of 600 ft. However the centerline lights were 'OTS' (NOTAM). I then queried the captain that this may be a case where the 12 and 10 rule applied since we had adequate centerline reference with centerline markings. He acknowledged that was correct. Fog began to lift rapidly with tower reported visibility at 1/4 mi we could count between 8 and 10 runway lights. Even though it appeared we had all the visual requirements to takeoff without restr RVR was still controling. We, through a misinterp of the rule took off with the understanding that the centerline reference requirement was met with centerline markings.

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Original NASA ASRS Text

Title: THE FLC OF AN ACR MISINTERPRETED THE MINIMUM WX AND VISUAL REF CRITERIA REQUIRED FOR A MINIMUM VISIBILITY TKOF.

Narrative: ARRIVED AT GSP ARPT AT XA15 AM FOR XB00 AM DEP AFTER SHORT OVERNIGHT. LOOKED AT WX AND CALLED COMPANY DISPATCH TO GET A TKOF ALTERNATE. THIS DISCUSSION TOOK SOME TIME BECAUSE MOST OF THE AREA ARPTS HAD LOW VISIBILITY. ARRIVED AT COCKPIT, FO ADVISED THE RVR WAS 1200 FT AND WE NEEDED AT LEAST 1600 FT TO DEPART. WE COMPLETED THE PREFLT PROCS AND CALLED FOR PUSHBACK CLRNC FROM GSP GND CTL. WE WERE CLRED TO TAXI AND ADVISED THE RVR WAS 1600 FT. AT THE END OF THE RWY RVR DROPPED TO 800 FT. SEVERAL CIVILIAN ACFT TOOK OFF, AND RPTED TOPS AT 50 FT AGL. TWR RPTED RVR IMPROVING TO 1200/1400 FT, AND CLRED US FOR TKOF. AFTER AIRBORNE I REALIZED WE NEEDED 1600 FT RVR TO DEPART. THIS WAS A CONFUSION OF 1200/1000 FT RVR WITH CTRLINE OPERATING BUT RWY MARKINGS OBSCURED BY CONTAMINANTS, BY MYSELF AND THE FO. THIS RWY IS GOOD FOR 600 FT RVR WITH CTRLINE LIGHTS OPERATING BUT THEY WERE OTS. WE COULD SEE APPROX 10 RWY LIGHTS WHEN WE TOOK THE RWY WHICH WOULD BE ABOUT 2000 FT RVR. THE TKOF WAS UNEVENTFUL AND WE WERE OUT OF THE FOG AFTER ROTATION. SUPPLEMENTAL INFO FROM ACN 297400: DURING PREFLT PREPARATION ATIS RPTED RVR AT 1000 FT. THE RWY IN USE HAS PUBLISHED TKOF MINS OF 600 FT. HOWEVER THE CTRLINE LIGHTS WERE 'OTS' (NOTAM). I THEN QUERIED THE CAPT THAT THIS MAY BE A CASE WHERE THE 12 AND 10 RULE APPLIED SINCE WE HAD ADEQUATE CTRLINE REF WITH CTRLINE MARKINGS. HE ACKNOWLEDGED THAT WAS CORRECT. FOG BEGAN TO LIFT RAPIDLY WITH TWR RPTED VISIBILITY AT 1/4 MI WE COULD COUNT BTWN 8 AND 10 RWY LIGHTS. EVEN THOUGH IT APPEARED WE HAD ALL THE VISUAL REQUIREMENTS TO TKOF WITHOUT RESTR RVR WAS STILL CTLING. WE, THROUGH A MISINTERP OF THE RULE TOOK OFF WITH THE UNDERSTANDING THAT THE CTRLINE REF REQUIREMENT WAS MET WITH CTRLINE MARKINGS.

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