INEXPERIENCED PLT OF C172; ATTEMPTING SHORT FIELD LNDG DURING TURBULENT CONDITIONS IS STRUCK BY 4 FT TALL SIGN SHORT OF RWY.

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WHILE ON SHORT FINAL FOR RWY 15 AT THE TN08 ARPT; I ENCOUNTERED A SEVERE DOWNDRAFT AND CONTACTED A METAL AND WOOD SIGN AT THE APCH END OF THE RWY. THE SIGN WAS APPROX 4 FT HIGH. FACTORS LEADING TO THIS EVENT INCLUDED THE TURBULENT CONDITIONS IN THE SURROUNDING MOUNTAINOUS TERRAIN; AND THE SIGN; WHICH SHOULD NOT HAVE BEEN THERE; AS IT WAS INTERFERING WITH THE GLIDE PATH FOR A LNDG AT THE END OF THE RWY. I SHOULD HAVE LEFT A LITTLE BIT MORE ALT; BUT I WOULD HAVE CLRED THE SIGN IF NOT FOR THE SUDDEN ENCOUNTER WITH THE DOWNDRAFT. I WAS ATTEMPTING TO LAND ON THE END OF THE RWY CONFIGURED FOR A SOFT FIELD CONDITION; THE FIELD IS GRASS; IT IS SHORT (APPROX 2500 FT USABLE); AND IT WAS SOFT. I BELIEVE THE MAIN CAUSE OF THIS HAPPENING WAS THAT THE SIGN WAS THERE IN THE FIRST PLACE. I WAS MAINTAINING A SLOW AIRSPD ON APCH; AIMING TO TOUCH DOWN IN SOFT FIELD CONFIGN; AND BEGINNING TO ROUND OUT; WHEN I ENCOUNTERED THE DOWNDRAFT CONDITION. DUE TO MY SLOW AIRSPD AND PROX TO THE SIGN; THERE WAS REALLY NOTHING I COULD HAVE DONE TO PREVENT IT; THE SINKING AIR AT THE END OF THE RWY WAS VERY STRONG. I BALLOONED AFTER CONTACTING THE SIGN AND I BELIEVE THE SUBSEQUENT HARD TOUCHDOWN ON THE SOFT FIELD PLAYED A PART IN DAMAGING THE WHEEL PANTS. UPON INSPECTION BY MY A&P MECH; NO DAMAGE WAS FOUND TO BE DONE TO THE ACFT OTHER THAN THE BROKEN WHEEL PANTS. THE EVENT WAS OVER WITH BEFORE I COULD DO ANYTHING TO STOP IT. I BELIEVE A MAJOR SIGNIFICANT FACTOR IN THIS EVENT WAS THAT THE SIGN WAS WHERE IT SHOULDN'T HAVE BEEN. THE OTHER MAJOR FACTOR WAS THE WIND CONDITIONS AND MY FAILURE TO ANTICIPATE DOWNDRAFT CONDITIONS. TO PREVENT SUCH HAPPENINGS IN THE FUTURE; I WILL LEAVE A LITTLE BIT MORE ROOM FOR OBSTACLES; AND COMPENSATE BETTER FOR WIND CONDITIONS. I BELIEVE THAT HAPPENINGS LIKE THESE COULD BE ELIMINATED ALTOGETHER IF THERE WAS A CONSCIOUS EFFORT BY AVIATION REGULATORY BODIES IN INSPECTING EVERY ARPT; PUBLIC OR PVT; FOR SAFETY CONDITIONS AND REQUIRING THAT PVT AIRFIELDS MEET THE SAME SAFETY STANDARDS (CLR FINAL APCH PATH WITH NO OBSTRUCTIONS AT ENDS OF RWYS) AS PUBLIC ARPTS AND NOT ALLOWING AIRFIELD THAT DO NOT UPHOLD MINIMUM SAFETY STANDARDS TO OPERATE.