AIR TAXI CARGO FLT HAS HARD LNDG DUE APPARENT LLWS. GEAR COLLAPSE ON BOUNCE BACK.

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HNL CTR HAD JUST GIVEN AN INTERISLAND COMPANY FLT A LNV WX BRIEF AND ASKED IF I HAD HEARD IT. I CONFIRMED I HAD; IT WAS THE SAME INFO I HAD RECEIVED FROM FSS BEFORE LEAVING HNL. CTR ALSO ASKED THE WX AND VIZ E OF MY POS WHICH I PROVIDED. LNY WAS PARTLY OVCST ESPECIALLY S AND E OF THE VOR SO I DSNDED TO 500 FT AND FLEW TO MADELE BAY TO CHK THE POSSIBILITY OF AN APCH TO RWY 21 FROM THE S. DURING THIS TIME A COMMERCIAL COMPANY CALLED AND ASKED HOW LNY LOOKED. THE AREA S OF LANAI AND E WAS VERY CLR BUT A L TFC PATTERN ENTRY TO RWY 21 DIDN'T SEEM ADVISABLE DUE TO INTERMITTENT LOW CLOUDS. SO I TURNED AROUND; FLEW NW AROUND PALAOA POINT TO CHK IF A RWY 3 APCH WAS POSSIBLE THE CEILINGS WERE IMPROVED AND I CLBED TO 2000 AGL OVER THE BARGE HARBOR. FROM THERE I WAS ABLE TO SEE THE ENTIRE ARPT AND LANAI CITY TO THE E SO I ENTERED A L BASE FOR RWY 3 AND PREPARED TO LAND. THE APCH WAS NORMAL WITH WINDS VARIABLE BUT NEARING APPROX 110 DEG AT 10 KTS. JUST BEFORE TOUCHDOWN I ENCOUNTERED AN EXTREMELY STRONG GUST OF WIND FROM MY R. I CORRECTED FOR THE GUST; THE WIND APPEARED TO STOP FROM WHAT I BELIEVE WAS LLWS. THE PLANE DROPPED WITH NO WARNING (MY AIRSPD WAS 100 KIAS) AND I HIT THE RWY HARD. I ATTEMPTED TO KEEP THE NOSE UP BUT THE PLANE BOUNCED HARD AGAIN AND I BELIEVE THE L MAIN GEAR COLLAPSED. DURING THE NEXT FEW SECONDS I ATTEMPTED TO KEEP CTL WHILE TURNING OFF THE FUEL VALVES; MIXTURE CTLS AND ALL ELECTRICAL SWITCHES. THE PLANE SKIDDED DOWN THE RWY THEN SLID L FROM THE RWY ACROSS THE SHOULDER UNTIL IT CAME TO REST. I VERIFIED ALL SWITCHES WERE OFF AND EXITED THE AIRPLANE. THERE WAS NO FUEL LEAKAGE SO I SECURED THE PLANE AND WALKED BACK TO THE TERMINAL AND ARPT FIRE DEPT WHERE I RPTED THE SITUATION. I THEN CALLED THE OWNER OF COMPANY AND INFORMED HIM WHAT HAPPENED. APPROX 15 MINS LATER; CAPT OF THE LANAI CITY FIRE DEPT SHOWED UP AND TOLD THE ARPT FIRE PERSONNEL AND I; HE HAD WITNESSED THE SITUATION. HE STATED HE WAS WATCHING THE LNDG WHICH APPEARED NORMAL WHEN SUDDENLY THE PLANE DROPPED TO THE RWY AND BOUNCED. HE HAS AGREED TO MAKE A STATEMENT. HE LATER ADVISED THERE WAS ANOTHER EYE WITNESS WITH HIM; A MR Y; WHO WOULD ALSO PREPARE A STATEMENT. TO PREVENT RECURRENCE; RECOMMEND: REMOVE THE SMALL HILL WHICH RUNS PARALLEL TO RWY 3 ON THE S SIDE FOR APPROX 500-1000 FT. IT'S PRESENCE WILL/DOES PROMOTE WIND SHEAR DURING S WIND CONDITIONS.