FLT INSTRUCTOR ON A DUAL XCOUNTRY ALLOWED THE STUDENT TO LAND BELOW WX MINS.

Narrative

DEPARTED GGG FOR DFW ON DUAL VFR TRAINING FLT; EXPECTED RETURN TIME WAS W (L) WX BRIEF GAVE N INDICATION OF FLT PRECAUTIONS FOR FOG OR RESTR VISIBILITY. VISIBILITY ON DEP WAS MVFR AND INCREASED STEADILY UNTIL WE HAD 20 PLUS MI VISIBILITY AT DFW. RETURN FLT WAS ABOUT THE SAME. HAD FLT FOLLOWING FROM FORT WORTH CTR. DUE TO INADEQUATE HDG CTL; STUDENT GOT APPROX 15 MI OFF COURSE AND FORT WORTH CTR ADVISED US OF THE ERROR AND OFFERED A RECOMMENDED VECTOR. MINS LATER WE HAD GGG IN SIGHT AND WE CANCELLED RADAR SVC. ZFW OFFERED NO TA'S. THERE ARE NO LCL WX RPTS FOR GGG AFTER 2200 (L) BUT LAST RPTED WINDS WERE CALM. VISIBILITY WAS ABOUT 5 NM IN THE TFC PATTERN; BUT WE COULD TELL THAT THE VISIBILITY ON THE GND WAS REDUCED DUE TO THE 'FUZZY' APPEARANCE OF THE LIGHTS ON THE ARPT. UPON COMPLETION OF THE PRELNDG CHK; WE DISCOVERED THAT THE LNDG LIGHT WAS INOPERATIVE (THOUGH IT DID WORK ON DEP FROM DFW). ON SHORT FINAL VISIBILITY DROPPED TO 2 MI (YOU COULD JUST SEE THE END OF THE RWY LIGHTS; RWY 13 -- 10000 FT LONG). AS WE TRANSITIONED TO THE LNDG FLARE WE SETTLED INTO A GND FOG. VISIBILITY DROPPED TO 1/2 MI AND ON ROLLOUT VISIBILITY DROPPED TO LESS THAN 1/8 MI. WE COULD NOT SEE ENOUGH TO TAXI CLR OF THE RWY. ABOUT THIS TIME A FLT RPTED INBOUND ON THE VOR-DME 31 APCH. WE RPTED TO HIM THAT WE HAD STILL NOT CLRED THE RWY. WE THEN MADE A 180 DEG TURN AND TAXIED NW INTENDING TO EXIT AT THE END OF THE RWY. (TAXIWAY A AND APCH END OF 13). AS WE PASSED THE 2000 FT REMAINING SIGN FOR RWY 31 WE BROKE OUT INTO MUCH IMPROVED VISIBILITY AND TAXIED CLR OF THE RWY. AT THIS TIME THE RPTED ON A 5 MI FINAL AND THERE WAS NO CONFLICT. TAXIING TO OUR RAMP WAS AN ACFT WITHOUT A LNDG LIGHT AS WE HIT SCATTERED POCKETS OF DENSE FOG AND COULD NOT SEE THE TAXIWAY CTRLINE. FINALLY A BRIGHT HANDHELD FLASHLIGHT WAS USED TO ILLUMINATE THE TAXIWAY. I AM CONVINCED THAT THE FLT WAS DONE COMPLETELY WITHIN THE FAR'S WITH THE EXCEPTION OF THE LAST 10-20 FT ABOVE THE GND. ADMITTEDLY THE TOUCHDOWN VISIBILITY WAS LESS THAN A MI; AND A GAR WAS PROBABLY WARRANTED.