Narrative:

At the scheduled time of our departure from mcallen, tx, the current WX report (ATIS) indicated a visibility of 1/8 SM in fog. Taxiing out for runway 13 we found conditions were variable but were below the 1/4 mi necessary for departure. After assessing the situation I elected to hold in the run-up area until visibility improved. After waiting for a little over 1 hour we noted that conditions had improved. The sun was now up and the surface wind had picked up to 5 KTS. Also, a cessna landed out of an ILS approach and reported picking up the runway at decision ht and that visibility down the runway was 'good.' from our position I was looking across the touchdown zone, counting runway edge lights. When we picked out the 7TH light I estimated the visibility at better than 1400 ft. Taxiing into position on runway 13 both the first officer and I could see past the 8TH edge light. At 200 ft between lights this worked out to more than 1600 ft or 1/4 mi, the minimums allowed for departure. I advised the tower of the visibility and requested a takeoff clearance. Mcallen does not have RVR, no RVV was given. The high intensity runway lights were working and the runway centerline markings were clearly visible. During the takeoff roll we had adequate forward visibility for a safe departure. The problem here is that I confused the requirements of far 121.651, paragraph (a) with the provisions of paragraph (B). Takeoff minimums are based on reported visibility, an approach and landing can be completed based on the pilot's assessment of actual conditions if the reported WX goes below minimums after the aircraft has begun the final approach segment of an instrument approach procedure. (Reference 121.651(C).) a quick check of our company's flight operations manual prior to the mfe departure did not dispel my confusion on this issue. Rereading the far's has clearly shown that I was in error. My mistake was not intentional but one of misunderstanding.

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Original NASA ASRS Text

Title: ACR FLT DEPARTS IN IMC WITHOUT LEGALLY RPTED TKOF MINIMUMS AS REQUIRED TO BE RPTED BY ATC.

Narrative: AT THE SCHEDULED TIME OF OUR DEP FROM MCALLEN, TX, THE CURRENT WX RPT (ATIS) INDICATED A VISIBILITY OF 1/8 SM IN FOG. TAXIING OUT FOR RWY 13 WE FOUND CONDITIONS WERE VARIABLE BUT WERE BELOW THE 1/4 MI NECESSARY FOR DEP. AFTER ASSESSING THE SIT I ELECTED TO HOLD IN THE RUN-UP AREA UNTIL VISIBILITY IMPROVED. AFTER WAITING FOR A LITTLE OVER 1 HR WE NOTED THAT CONDITIONS HAD IMPROVED. THE SUN WAS NOW UP AND THE SURFACE WIND HAD PICKED UP TO 5 KTS. ALSO, A CESSNA LANDED OUT OF AN ILS APCH AND RPTED PICKING UP THE RWY AT DECISION HT AND THAT VISIBILITY DOWN THE RWY WAS 'GOOD.' FROM OUR POS I WAS LOOKING ACROSS THE TOUCHDOWN ZONE, COUNTING RWY EDGE LIGHTS. WHEN WE PICKED OUT THE 7TH LIGHT I ESTIMATED THE VISIBILITY AT BETTER THAN 1400 FT. TAXIING INTO POS ON RWY 13 BOTH THE FO AND I COULD SEE PAST THE 8TH EDGE LIGHT. AT 200 FT BTWN LIGHTS THIS WORKED OUT TO MORE THAN 1600 FT OR 1/4 MI, THE MINIMUMS ALLOWED FOR DEP. I ADVISED THE TWR OF THE VISIBILITY AND REQUESTED A TKOF CLRNC. MCALLEN DOES NOT HAVE RVR, NO RVV WAS GIVEN. THE HIGH INTENSITY RWY LIGHTS WERE WORKING AND THE RWY CTRLINE MARKINGS WERE CLRLY VISIBLE. DURING THE TKOF ROLL WE HAD ADEQUATE FORWARD VISIBILITY FOR A SAFE DEP. THE PROB HERE IS THAT I CONFUSED THE REQUIREMENTS OF FAR 121.651, PARAGRAPH (A) WITH THE PROVISIONS OF PARAGRAPH (B). TKOF MINIMUMS ARE BASED ON RPTED VISIBILITY, AN APCH AND LNDG CAN BE COMPLETED BASED ON THE PLT'S ASSESSMENT OF ACTUAL CONDITIONS IF THE RPTED WX GOES BELOW MINIMUMS AFTER THE ACFT HAS BEGUN THE FINAL APCH SEGMENT OF AN INST APCH PROC. (REF 121.651(C).) A QUICK CHK OF OUR COMPANY'S FLT OPS MANUAL PRIOR TO THE MFE DEP DID NOT DISPEL MY CONFUSION ON THIS ISSUE. REREADING THE FAR'S HAS CLRLY SHOWN THAT I WAS IN ERROR. MY MISTAKE WAS NOT INTENTIONAL BUT ONE OF MISUNDERSTANDING.

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.