MOONEY PLT ENCOUNTERS SEVERE DOWNDRAFT OVER RWY THRESHOLD ON APCH TO LNDG. HARD LNDG AND PORPOISING RESULTS IN LOSS OF ACFT CTL. RWY ENVIRONMENT CREATES DOWNDRAFT. HARD LNDG.

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UPON ARR AT BLAKELY ISLAND FROM THE S; I OVERPASSED THE AIRFIELD (ALT 66 FT) AT 1500 FT AND INSPECTED WINDSOCKS AND WATER SURFACE WHITECAPS AND CONFIRMED A STRONG WIND FROM THE N; FAVORING RWY 1 APCH. APCH SPD WAS 90 MPH DOWNWIND; BASE AND TURN TO FINAL. I ADDED SECOND HALF OF FULL FLAPS AND REDUCED AIRSPD TO 80 MPH; WITH DSCNT SUPPLEMENTED USING SLIP TECHNIQUE. WIND WAS ESTIMATED TO BE 15 KTS GUSTING TO 20 KTS; DIRECTLY DOWN THE RWY. LARGE TREES WERE NOTED ON EACH SIDE OF THE AIRFIELD; BUT WITH A CTRLINE WIND; I JUDGED THESE TO HAVE LITTLE INFLUENCE ON WIND EFFECT BELOW TREE LEVEL. GUMP CHKLIST ON FINAL WAS DONE. I STRAIGHTENED THE SLIP ABOUT MIDWAY THROUGH THE FINAL APCH. FINAL APCH SPD WAS 80 MPH WITH EXCELLENT DSCNT FLT PATH AND ACFT ATTITUDE. EVEN BELOW THE TREE LINE; THE ACFT TRACKED WELL ON FINAL. APPROX 20 FT ABOVE THRESHOLD; JUST AFTER I MENTALLY COMMITTED MYSELF TO THE LNDG; THE ACFT ENTERED INTO (THE SUBSEQUENTLY WELL KNOWN TO THE LCL AVIATORS) 'SINK HOLE' RESULTING FROM A SUDDEN REDUCTION IN HEAD WIND ('THE WIND JUST DIES AND SHEARS TO ZERO') SUPPLEMENTED BY THE LIKELY ROLL-EFFECT AS THE WIND PASSES OVER THE MIDFIELD ELEVATED RWY CREST AND ROLLS OVER WITH A DOWNWARD FORCE INTO THE LNDG ZONE. WHILE THE ACFT DSNDED QUITE RAPIDLY AND THE STALL HORN CAME ON; I'M SURE I ADDED SOME BACK PRESSURE ON THE YOKE. MORE IMPORTANTLY; I ADDED FULL THROTTLE PWR; WITH ENG ACCELERATION SEEMINGLY TO BE HEARD AND FELT AS THE ACFT HIT THE CTRLINE OF THE RWY. THE MAIN GEAR AND TAIL SECTION HIT AND BOUNCED; WITH A ROTATIONAL EFFECT ON THE FRONT PORTION OF THE ACFT CAUSING 3 RWY PROP STRIKES ON THE CTRLINE. THE ACFT VEERED TO THE L JUST AS THE EFFECTS OF FULL PWR CAME ON; AND THE ACFT WENT FROM A NOSE DOWN POS TO A PROMINENT NOSE UP ATTITUDE. ATTITUDE AND ROLL CTL SEEMED TO BE MORE RESPONSIVE; AND WITH ELEVATOR; RUDDER AND AILERON CTL; POSSIBLY WITH ENG P FACTOR; THE ACFT MOVED DECIDEDLY BACK OVER THE RWY AND STABILIZED. ALTHOUGH I WAS INTO THE PROCESS OF INITIATING A MISSED APCH; I ELECTED TO CUT PWR AND SETTLE BACK ONTO THE RWY; WITH A MUCH SMOOTHER AND CTLED LET-DOWN OF THE MAIN GEAR AND A CTLED NOSE-UP REDUCTION IN SPD WHILE TRACKING THE CTRLINE. BRAKING AND TAXI TO TIE DOWN PROCEEDED WITHOUT INCIDENT. POST-INCIDENT INSPECTION OF THE ACFT REVEALED PROP STRIKE DAMAGE; LNDG GEAR DOOR COVERS BENT; TAIL TIE DOWN RING AND BRACKET BENT; GEAR AND TIRES INTACT. STRUCTURAL AIRFRAME INTEGRITY APPEARED WELL INTACT. THERE WERE NO INJURIES. SEVERAL ISLAND RESIDENTS APCHED AND GAVE WITNESS DESCRIPTIONS. HEADWIND SHEARS TO CALM APPROX 20 FT ABOVE LNDG SPOT; SUDDEN LOSS OF LIFT; ALSO CAUSED BY DOWN ROTOR WIND EFFECT. AIRPLANE FALLS SUDDENLY 20 FT. UNFAMILIAR PLTS LNDG AT BLAKELY ISLAND OFTEN BEND PROPS OR EVEN BURN UP. NO MENTION OF THIS IN FAA'S FILE ON S08; AS I PREFLT CHKED FAA'S INTERNET FILE FOR ARPT DESCRIPTION.