SMA TWIN SUFFERS ACFT DAMAGE WHEN NOSE GEAR COLLAPSES DURING LNDG PROC ROLLOUT.

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ON LNDG AT SUN VALLEY ARPT (SUN); LOCATED IN HAILEY; ID; ALUMINUM FORK ATTACHMENT TO NOSEWHEEL OF 19XX SMA MODEL TWIN; BROKE; CAUSING NOSEWHEEL TO FALL OFF AND ACFT TO LAND ON NOSEWHEEL STRUT. PROPS AND NOSEWHEEL MECHANISM DAMAGED BY CONTACT WITH RWY; BUT NO OTHER DAMAGE TO AIRFRAME STRUCTURE. PLT WAS FLYING ALONE WITH NO BAGGAGE; AND ACFT WAS WELL UNDER GROSS WT. LNDG WAS WITH TAILWIND OF APPROX 8 KTS; BUT THIS IS COMMON AT SUN WHERE LNDGS ARE USUALLY MADE FROM THE S ON RWY 31. SUN IS PLT'S HOME ARPT; AND PLT HAS MADE NUMEROUS LNDGS THERE UNDER WORSE CONDITIONS. THIS WAS A BORROWED ACFT THAT PLT HAD FREQUENTLY FLOWN. OP OF NOSE GEAR WAS NORMAL ON TAXI AND TKOF AT REDMOND; OR (RDM) FOR THIS FLT; AND ON APCH AT SUN. NO BLOWOUT OR IMPACT TRAUMA FOUND ON SEPARATED NOSEWHEEL AND TIRE. PLT LEARNED AFTER THE INCIDENT THAT NOSE TIRE HAD BEEN REPLACED 30-60 DAYS EARLIER AFTER BLOWOUT DURING HARD NOSEWHEEL LNDG. THEREFORE; PLT SUSPECTS PREEXISTING METAL FATIGUE AND/OR UNDETECTED CRACK IN NOSEWHEEL FORK. NOSEWHEEL FORK WILL BE ANALYZED TO VERIFY THIS. NO INJURIES INVOLVED. WHEN IT BECAME OBVIOUS TO PLT ON TOUCHDOWN THAT NOSE GEAR HAD FAILED; ENGS WERE IMMEDIATELY SHUT DOWN; AND ALL ELECTRICAL AND FUEL SWITCHES WERE TURNED OFF. ACFT SKIDDED TO A STOP ON THE RWY; RIDING ON ITS WHEEL-LESS NOSEWHEEL STRUT. THIS CAUSED SPARKS BUT NO FIRE.