M20P PLT DEPARTS TMB VFR ENRTE TO HWO; BECOMES DISORIENTED; RELYING ON MALFUNCTIONING LORAN; PENETRATES THE MIA CLASS B PRIOR TO OBTAINING REORIENTATION FROM HWO TWR.

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PANEL MOUNTED GPS HAD FAILED. WAS RETURNING FROM TMB TO HWO HAVING L FILED UNIT AT AVIONICS REPAIR SHOP. DEPARTED RWY 9L AND PROCEEDED WNW AFTER L TURNOUT. CLBED TO 1300 FT AND REMAINED AT 1300 FT. AFTER PROCEEDING APPROX 6 MI; TURNED NNW AND COPIED HWO ATIS. LORAN UNIT SET TO HWO. CONTACTED HWO TWR AND WAS TOLD TO CONTACT WHEN 2 MI OUT FOR RWY 9R. TURNED E WHEN LORAN INDICATED HWO AT 91 DEGS. IMMEDIATELY SAW ARPT WITH 2 PARALLEL RWYS; EW; AND WAS PUZZLED AT SIZE. DOUBLE-CHKING LORAN; IT STILL INDICATED HWO DUE E. RECHKED CHART; LOOKING FOR OTHER LANDMARKS. NOTICED SKYLINE TO THE R OF ARPT AND IMMEDIATELY BEGAN TURN TO N AND ADVISED HWO TWR THAT 'I DON'T LIKE WHERE I AM; I THINK MY NAV'S WRONG!' ASKED IF THEY HAD ME ON RADAR. HWO ASKED FOR IDENT AND I COMPLIED. MOMENTS LATER; THEY ASKED FOR IDENT AGAIN AND I CONFIRMED THAT I HAD PRESSED IDENT. THE TWR INDICATED I WAS 3 MI W OF MIA AND ADVISED TURN TO N; WHICH I HAD ALREADY DONE. I PROCEEDED NW AT 1300 FT TO CLR THE B AIRSPACE. I THEN FOUND LANDMARKS AND PROCEEDED TO LAND SAFELY AT HWO. AS I APCHED HWO; LORAN INDICATED HWO AT 135 DEGS -- EVEN THOUGH I WAS DIRECTLY DUE W OF HWO. I CYCLED THE LORAN AND NOTICED THAT THE LORAN THEN READ HWO DUE E. OTHER FACTORS: 1) 15 KT SURFACE WINDS AND MOSTLY CLR SKIES MADE THE RIDE AT 1300 FT BUMPY -- LIGHT TURB. 2) HIGH DENSITY TRAINING AND TFC AREA JUST W OF PBI. MIA LINE REQUIRES VIGILANT SCANNING WHICH DETRACTED FROM NAV. 3) SHORT FLT AND 'FAMILIARITY' WITH AREA CAUSED LACK OF ATTN TO NAV. 4) 1-2 MIN DELAY BELIEVING MY EYES (MIA VERY BIG) AND DISCARDING THE FAULTY LORAN.