A HELI RPTS INCORRECT ACFT IN SIGHT; IS CLRED TO FOLLOW BUT IS SUBSEQUENTLY OVERFLOWN BY ACFT ATC THINKS HE IS FOLLOWING AND HAS IN SIGHT. THE SEPARATION IF 15 FT.

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XB15. AT 20 MI S OF LAKEFRONT ARPT; CONTACTED NEW ORLEANS APCH; WAS ISSUED A XPONDER CODE; AND CLRED INTO THE CLASS B AIRSPACE AT 2500 FT. INFORMED NEW ORLEANS APCH THAT ACFT WAS VFR TO LAKEFRONT ARPT WITH CURRENT ATIS INFO. INFORMED GRAND ISLE TWR OF POSITIVE CTL WITH NEW ORLEANS APCH. CLOSED FLT PLAN WITH GRAND ISLE TO REFLECT LNDG TIME AT LAKEFRONT ARPT OF XB25. TUNED SECOND VHF RADIO TO LAKEFRONT TWR FREQ TO MONITOR TFC. XB20 LCL. AT 8.7 MI S OF LAKEFRONT ARPT; WAS CONTACTED BY NEW ORLEANS APCH WITH UPDATED INFO ON TFC; AND TWR FREQ FOR LAKEFRONT ARPT. NEW ORLEANS APCH REQUESTED CONTACT WHEN LAKEFRONT ARPT WAS IN SIGHT. RPTED TO NEW ORLEANS APCH THAT LAKEFRONT ARPT WAS ALREADY IN SIGHT. AT 8.5 MI FROM LAKEFRONT ARPT; WAS INSTRUCTED BY NEW ORLEANS APCH TO CONTACT LAKEFRONT TWR. CONTACTED LAKEFRONT TWR WITH POS RPT; INTENTIONS; AND ATIS INFO. WAS INSTRUCTED TO EXPECT LNDG ON TXWY F R OF RWY 36L; AND RPT 2 MI OUT. CONFIRMED INSTRUCTIONS; REQUESTED AND RECEIVED PERMISSION TO START DSCNT FROM 2500 FT DOWN TO 500 FT. XB22. AFTER DSNDING FROM 2500 FT TO 1800 FT USING A DSCNT RATE OF APPROX 1000 FPM; WAS INFORMED TO FOLLOW BONANZA THAT WAS TURNING TO FINAL APCH AT 1500 FT. BONANZA COULD NOT BE LOCATED. THE FOLLOWING SEQUENCE OF EVENTS TOOK PLACE IN LESS THAN 10 SECONDS. TCAS AUDIO RPTED 'WARNING ACFT LESS THAN 1 MI.' CHK OF TCAS DISPLAY SHOWED NUMEROUS TARGETS. PAX POINTED TO THE L SIDE OF ACFT. BONANZA STILL NOT VISIBLE. INFORMED LAKEFRONT TWR OF INTENTIONS TO EXECUTE A R 360 DEG STANDARD RATE TURN FOR SPACING. LAKEFRONT TWR ACKNOWLEDGED INTENTIONS. GND SPD INDICATED 127 KTS. CHKED R SIDE OF ACFT TO CLR FOR SPACING TURN. WHILE SCANNING INSTS PRIOR TO EXECUTING SPACING TURN; BONANZA TRAVELING ON SAME HDG DSNDED FROM OVERHEAD WITH 15 FT OF MAIN ROTOR BLADES WITH GEAR UP. CONTACTED LAKEFRONT TWR WITH THE FOLLOWING STATEMENT: 'THAT WAS CLOSER THAN I THOUGHT!' THE BONANZA RPTED HE LOST SIGHT OF THE HELI IN THE TURN. SPACING TURN WAS NEVER EXECUTED. LAKEFRONT TWR INFORMED ANOTHER ACFT TO FOLLOW THE HELI IN ON APCH. XB25. LANDED AT LAKEFRONT WITHOUT FURTHER INCIDENT. [TWR SUPVR'S COMMENTS]: 'AFTER REVIEWING THE TAPES OF LAKEFRONT TWR FOR THE SATURDAY TIME FRAME; IT APPEARS THE HELI WAS IN ERROR.' 'ALL INSTRUCTIONS GIVEN TO THE HELI WERE BASED ON BARON TFC.' AT THIS POINT I READ MY EVENTS DETAILS TO TWR SUPVR STARTING AT THE SB20 LCL PARAGRAPH AND READING UNTIL THE END. AFTER HEARING THE EVENTS; TWR SUPVR MADE THE FOLLOWING OBSERVATIONS: TWR SUPVR SAID 'THE TFC INFO RELAYED TO YOU BY LAKEFRONT TWR WAS ABOUT A BARON ON EXTENDED L BASE TO RWY 36L.' 'HIS POS WAS RPTED AT 1500 FT AND IN FRONT OF YOU.' 'THERE WAS A BONANZA ON SHORT FINAL TO RWY 36L.' 'THE BONANZA WAS THE ACFT THAT YOU SAW BELOW; AND IN FRONT OF YOU.' 'BELIEVING THE BONANZA WAS THE BARON YOU WERE SUPPOSED TO FOLLOW; YOU GAVE A POSITIVE CONTACT; AND CONTINUED YOUR APCH.' 'A SECOND BONANZA WAS BEHIND YOU; FOLLOWED BY A MOONEY.' 'THESE ACFT WERE NOT A FACTOR; BUT ADDED TO THE CONFUSION.' 'SIMILAR TYPES OF ACFT DIFFERENT LOCATIONS IN SEQUENCING.' 'AT THIS POINT; EVENTS CONTINUED AS YOU MADE YOUR APCH; AND THE BARON PASSED YOU FROM OVERHEAD.' 'ALSO; LAKEFRONT TWR ADDRESSED YOUR ACFT CALL SIGN AXYZ AS BXYZ; AXYZ; AND CXYZ.' 'THIS ALSO ADDED TO THE CONFUSION.' 'AT THIS TIME; LAKEFRONT TWR VIEWS THIS AS A NON-EVENT.'