Narrative:

We flew to crw, charleston, wv. We could see the airport about 15 mi away, but the ATIS was reporting low visibility due to ground fog. We got an oral report from the tower who gave us a current prevailing visibility that was legal to start the approach. After 2 unsuccessful approachs, we diverted to our alternate, roanoke. A week later, someone questioned if we were legal to start the approach. Our FAA approved flight operations policies and procedures says 'an oral report from the tower contains a visibility value specified as runway visibility or runway visual range for a particular runway at an airport, that specified value is controling for takeoffs, lndgs.' based on this statement, I believed I was legal because it says either runway visibility or RVR can be controling and does not specify which is more restrictive if both prevailing visibility and RVR are reported. However, after checking with our chief pilot for clarification, he said RVR is always controling, regardless whether it is more or less restrictive than reported prevailing visibility. I remember the controller reported both runway visibility and RVR. I do not remember what his RVR report was. I remember his runway visibility was legal and, based on our manual, I thought the approach was legal. However, it may not have been legal based on the RVR report. This problem arose due to inadequate guidance in our operations manual (it only specifies when you have 1 report or the other, but not when you're given both). Additionally, if we had discussed and/or role played this scenario in our airline's ground school, the ambiguity would have been clarified. Supplemental information from acn 618308: after reviewing the situation, I realized there may have been a discrepancy between ATIS and tower reported RVR.

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Original NASA ASRS Text

Title: DIVERSION TO ALTERNATE DURING A NIGHT OP AFTER AN SF340 FLT CREW MAKES 2 ATTEMPTS FOR AN ILS RWY 23, QUESTIONING THEMSELVES IF THE APCH WAS LEGAL BASED UPON THE RVR GIVEN BY TWR AT CRW, WV.

Narrative: WE FLEW TO CRW, CHARLESTON, WV. WE COULD SEE THE ARPT ABOUT 15 MI AWAY, BUT THE ATIS WAS RPTING LOW VISIBILITY DUE TO GND FOG. WE GOT AN ORAL RPT FROM THE TWR WHO GAVE US A CURRENT PREVAILING VISIBILITY THAT WAS LEGAL TO START THE APCH. AFTER 2 UNSUCCESSFUL APCHS, WE DIVERTED TO OUR ALTERNATE, ROANOKE. A WK LATER, SOMEONE QUESTIONED IF WE WERE LEGAL TO START THE APCH. OUR FAA APPROVED FLT OPS POLICIES AND PROCS SAYS 'AN ORAL RPT FROM THE TWR CONTAINS A VISIBILITY VALUE SPECIFIED AS RWY VISIBILITY OR RWY VISUAL RANGE FOR A PARTICULAR RWY AT AN ARPT, THAT SPECIFIED VALUE IS CTLING FOR TKOFS, LNDGS.' BASED ON THIS STATEMENT, I BELIEVED I WAS LEGAL BECAUSE IT SAYS EITHER RWY VISIBILITY OR RVR CAN BE CTLING AND DOES NOT SPECIFY WHICH IS MORE RESTRICTIVE IF BOTH PREVAILING VISIBILITY AND RVR ARE RPTED. HOWEVER, AFTER CHKING WITH OUR CHIEF PLT FOR CLARIFICATION, HE SAID RVR IS ALWAYS CTLING, REGARDLESS WHETHER IT IS MORE OR LESS RESTRICTIVE THAN RPTED PREVAILING VISIBILITY. I REMEMBER THE CTLR RPTED BOTH RWY VISIBILITY AND RVR. I DO NOT REMEMBER WHAT HIS RVR RPT WAS. I REMEMBER HIS RWY VISIBILITY WAS LEGAL AND, BASED ON OUR MANUAL, I THOUGHT THE APCH WAS LEGAL. HOWEVER, IT MAY NOT HAVE BEEN LEGAL BASED ON THE RVR RPT. THIS PROB AROSE DUE TO INADEQUATE GUIDANCE IN OUR OPS MANUAL (IT ONLY SPECIFIES WHEN YOU HAVE 1 RPT OR THE OTHER, BUT NOT WHEN YOU'RE GIVEN BOTH). ADDITIONALLY, IF WE HAD DISCUSSED AND/OR ROLE PLAYED THIS SCENARIO IN OUR AIRLINE'S GND SCHOOL, THE AMBIGUITY WOULD HAVE BEEN CLARIFIED. SUPPLEMENTAL INFO FROM ACN 618308: AFTER REVIEWING THE SIT, I REALIZED THERE MAY HAVE BEEN A DISCREPANCY BTWN ATIS AND TWR RPTED RVR.

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.