C172 AND A SAILPLANE ALMOST COLLIDED AT ZPH.

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AT APPROX XA00 ON SUNDAY JUNE 2000 I HAD JUST LANDED MY ACFT; A CESSNA 172; ON RWY 22 IN ZEPHYRHILLS ARPT. IN THE R SEAT WAS MY WIFE; ALSO A PRIVATE PLT. I TURNED OFF RWY 22 ONTO A TXWY AND PROCEEDED ESE WHERE WE PLANNED TO CHANGE SEATS NEAR THE PARACHUTE FACILITY ON THE FIELD. OUR TXWY CROSSED THE THRESHOLD OF RWY 36 PRIOR TO THE PARACHUTE AREA. AS THE TXWY APCHED THE INTXN OF RWY 36 MY WIFE AND I SEARCHED FOR LNDG TFC ON RWY 36; AS WELL LOOKING FOR ANY PARACHUTERS IN THE AREA. HAVING HEARD NO RADIO TFC RPTS AND SEEING NO APCHING ACFT; I CROSSED THE LINE ONTO RWY 36. I THEN SAW A SAILPLANE ON VERY SHORT FINAL WHO APPEARED TO BE INTENDING OT LAND ON THE GRASSY AREA SHORT OF THE APCH END OF RWY 36. THE SAILPLANE WAS ABOUT THREE FT OVER THE GRASS AND ABOUT 30 FT FROM THE THRESHOLD OF RWY 36 WHEN I FIRST SAW HIM. I IMMEDIATELY BRAKED TO A STOP; WITH MY NOSE WHEEL OVER ONTO THE ACTIVE RWY 36. MY WINGS AND TAIL SECTION WERE STILL ON THE TXWY SIDE OF THE RWY MARGIN LINES WHEN MY ACFT STOPPED. THE SAILPLANE PLT THEN INITIATED A CLIMB AND PASSED IN FRONT AND ABOUT 20 FT ABOVE MY ACFT AND THEN LANDED UNEVENTFULLY ON THE 36 CTRLINE WHEN WELL PAST THE TXWY RWY INTXN. CONTRIBUTING FACTORS: SINCE BOTH MY WIFE; (ALSO A PLT); AND MYSELF ACTIVELY SCANNED FOR LNDG TFC BEFORE PROCEEDING ONTO THE ACTIVE RWY; I CAN ONLY SPECULATE AS TO WHAT EXTENT THE FOLLOWING FACTORS MY HAVE PLAYED IN MY INABILITY TO VISUALLY ACQUIRE THE TFC IN TIME TO STOP SHORT OF THE RWY. 1 THE SMALL CROSS SECTION OF THE SAILPLANE. WHEN VIEWED 'HEAD ON'; A SAILPLANE PRESENTS A VERY SMALL VISUAL TARGET. 2 A LARGE FOREST FIRE BURNED TO THE SOUTHEAST OF THE ARPT MAKING THE SKY GRAY WITH SMOKE. THIS MAY HAVE REDUCED THE CONTRAST BETWEEN THE ACFT AND THE SKY. 3 SINCE THE SAILPLANE APPEARED TO BE LNDG IN THE GRASS SHORT OF THE RWY THRESHOLD; HIS LOCATION ON SHORT FINAL MAY HAVE BEEN IN AND ATYPICAL POSITION IN REFERENCE TO THE HORIZON; THUS MAKING IT MORE DIFFICULT TO VISUALLY ACQUIRE. THE SAILPLANE MAY HAVE BEEN BELOW THE HORIZON-LINE; (TREES); AS SEEN FROM MY PLANE AS WE APCHED THE RWY INTXN. THE SAILPLANE WAS DEFINITELY WELL BELOW THE HORIZON-LINE WHEN I FIRST SAW HIM. THE SAILPLANE'S INABILITY TO MAKE A RADIO POS RPT IN THE PATTERN ELIMINATED AN IMPORTANT CLUE TO TFC POS AWARENESS FOR ALL PLTS UTILIZING THE ARPT. CORRECTIVE ACTION: 1 MY APPLICATION OF BRAKES BRINGING MY ACFT TO A STOP PRIOR TO A POTENTIAL COLLISION POINT ON THE RWY. 2 THE SAILPLANE PLT'S ASCENDING MANEUVER TO AVOID A POTENTIAL ACCIDENT IF MY ACFT HAD NOT STOPPED.