RWY EXCURSION.

Narrative

I WAS ON AN ILS APCH INTO LEWISTON; ID. WX WAS RPTED AS INDEFINITE CEILING AND 1/8 MI VISIBILITY IN FOG. THE APCH WAS NORMAL. AT DECISION HT I COULD SEE THE RWY CTRLINES AND THE EDGE LIGHTS. I ELECTED TO LAND. AT THIS POINT I RELAXED AND BECAME A BIT COMPLACENT; MEANING I DID NOT GET THE ACFT QUICKLY ON THE GND BUT INSTEAD DSNDED SLOWLY AND TRIED TO 'GREASE' THE ACFT ON. ONCE ON THE GND I APPLIED THE BRAKES LIGHTLY AND HAD THE THROTTLES BACK TO THE STOPS. I WAS MENTALLY LETTING THE ACFT ROLLOUT TO THE END OF THE RWY. IT WAS SHORTLY THEREAFTER THAT I COULD SEE THE END OF THE RWY LOOMING UPON ME. I DID NOT EXPECT THE END SO SOON. I DID NOT REALIZE HOW FAR DOWN THE RWY I WAS. I THEN GOT HARD ON THE BRAKES AND PULLED THE PROPS INTO REVERSE. I WAS UNABLE TO GET STOPPED ON THE RWY AND ENDED UP ABOUT 15 FT BEYOND THE END OF THE RWY. THE R HAND PROP TIPS STRUCK SOME LOOSE GRAVEL BUT THERE WAS NO OTHER DAMAGE AND NO HARM TO ANYONE ABOARD. IN RETROSPECT I CAN SEE SEVERAL ERRORS THAT I MADE. I FAILED TO MONITOR MY AIRSPD INDICATOR ONCE ON THE GND BUT INSTEAD RELIED UPON MY VISUAL PERCEPTION OF MY SPD. BECAUSE VISIBILITY WAS LOW AND THERE WAS VERY LITTLE DISTANCE THAT I COULD SEE I FEEL I MISJUDGED OUR SPD ON THE GND WHICH LED TO MY ALLOWING US TO GET INTO THE SIT OF TOO MUCH SPD AND TOO LITTLE RWY. ALSO BECAUSE OF MY MINDSET THAT I HAD PLENTY OF RWY I DID NOT SEE THE CHANGE IN RWY EDGE LIGHTS FROM WHITE TO AMBER; WHICH WOULD HAVE GIVEN ME AN IDEA OF MY TRUE POS. COMPLACENCY AND MISPERCEPTION ON MY PART COUPLED WITH LOW VISIBILITY CONDITIONS WERE THE MAIN CONTRIBUTING FACTORS TO THE ABOVE SIT.