FLC OF AN MLG ACR ACFT TOUCHED DOWN ON THE RWY BRIEFLY DURING A MISSED APCH GAR RESULTING IN NO DAMAGE TO THE ACFT.

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AS THE ACFT APCHED DFW WE RECEIVED VECTORS FOR RWY 17R. RPTED WX CHANGED SEVERAL TIMES DURING VECTORS PRIOR TO LOC INTERCEPT. ATC ASKED IF WE WISHED TO LAND RWY 18L. ATC GAVE RWY 18L RVR OF BETTER THAN 6000/6000/6000. ATC INDICATED THAT RVR TO RWY 17R WAS LESS THAN 2300 FT AND GETTING WORSE. WE ELECTED TO ACCEPT RWY 18L. THE ACFT WAS CONFIGURED ON SCHEDULE TO FLAPS 30 DEGS AS BRIEFED. I BEGAN TO REPROGRAM THE COMPUTER FOR RWY 18L IN ORDER TO OBTAIN IMPROVED SIT AWARENESS (VERT DISPLACEMENT IN FEET). THIS TASK WAS COMPLICATED BY AN INOPERATIVE 'EXECUTE' BUTTON ON MY COMMAND DISPLAY UNIT. THE CAPT REQUESTED FLAPS 40 DEGS AND BRIEFED A NEW APCH SPD. I SELECTED FLAPS 40 DEGS AND CONTINUED REPROGRAMMING THE COMPUTER. RWY APCH LIGHTS COULD BE SEEN ILLUMINATING A THIN LAYER OF FOG. WE WERE STILL VMC. I HEARD THE GND PROX WARNING SOUND. I SCANNED THE INSTS AND SAW THE CAPT BEGIN RAISING THE NOSE AND ADVANCING THE THRUST LEVERS. SIMULTANEOUSLY THE APCH LIGHTS CAME INTO FULL VIEW. I PERCEIVED THAT THE ACFT WAS DSNDING AND I IMMEDIATELY ADVANCED THE THRUST LEVERS TO 'FIRE WALL THRUST' AND FORCEFULLY PULLED THE ACFT YOKE BACK. WE TOUCHED THE GND BRIEFLY AND THEN THE ACFT BECAME AIRBORNE AGAIN. I RPTED MISSED APCH AND CLEANED UP THE ACFT ON SCHEDULE. AFTER DETERMINING THE ACFT WAS STABILIZED AND FLT CAPABLE; WE ELECTED TO FLY TO IAH TO ALLOW FOR VISUAL INSPECTION OF MAIN LNDG GEAR PRIOR TO LNDG.