Narrative:

My aircraft was towing a banner sbound on the bravo route (a route between crystal pier and the ocean beach pier). Lindbergh tower had given me a squawk and a clearance to enter class B airspace in accordance with the LOA (LOA prescribes route along shoreline at or below 500 ft AGL). I was given no further advisories. As my flight crossed the ocean beach pier, lindbergh tower began to receive xmissions from an angry coast guard helicopter claiming that they had missed my banner by 'no less than 100 ft.' until this point I was completely unaware of the helicopter, and apparently they had not been informed of my presence. I think what occurred here was due, in large part, to a controller change during flight between the piers. I think what may have happened, and this cannot be verified, was that the coast guard helicopter had been operating for several mins at low altitude and had not spoken to lindbergh for some time. The low altitude caused the helicopter to drop-off of radar, and the duration of radio silence combined with the controller change, simply caused the helicopter to be 'forgotten.' thus, neither the helicopter, nor myself was informed of the other. Note: normal procedure on the bravo route is not to allow any aircraft to enter unless they have other aircraft 'in sight,' or unless aircraft already on the bravo route have the arriving aircraft 'in sight.' in hundreds of flts on the bravo route, this is my first experience with such a situation.

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Original NASA ASRS Text

Title: NMAC BTWN A BANNER TOWING CESSNA 182 AND A MIL HELI IN CLASS B AIRSPACE. CAUSED BY ATC NOT ADVISING THE 2 ACFT FLC OF THE OTHER'S PRESENCE.

Narrative: MY ACFT WAS TOWING A BANNER SBOUND ON THE BRAVO RTE (A RTE BTWN CRYSTAL PIER AND THE OCEAN BEACH PIER). LINDBERGH TWR HAD GIVEN ME A SQUAWK AND A CLRNC TO ENTER CLASS B AIRSPACE IN ACCORDANCE WITH THE LOA (LOA PRESCRIBES RTE ALONG SHORELINE AT OR BELOW 500 FT AGL). I WAS GIVEN NO FURTHER ADVISORIES. AS MY FLT CROSSED THE OCEAN BEACH PIER, LINDBERGH TWR BEGAN TO RECEIVE XMISSIONS FROM AN ANGRY COAST GUARD HELI CLAIMING THAT THEY HAD MISSED MY BANNER BY 'NO LESS THAN 100 FT.' UNTIL THIS POINT I WAS COMPLETELY UNAWARE OF THE HELI, AND APPARENTLY THEY HAD NOT BEEN INFORMED OF MY PRESENCE. I THINK WHAT OCCURRED HERE WAS DUE, IN LARGE PART, TO A CTLR CHANGE DURING FLT BTWN THE PIERS. I THINK WHAT MAY HAVE HAPPENED, AND THIS CANNOT BE VERIFIED, WAS THAT THE COAST GUARD HELI HAD BEEN OPERATING FOR SEVERAL MINS AT LOW ALT AND HAD NOT SPOKEN TO LINDBERGH FOR SOME TIME. THE LOW ALT CAUSED THE HELI TO DROP-OFF OF RADAR, AND THE DURATION OF RADIO SILENCE COMBINED WITH THE CTLR CHANGE, SIMPLY CAUSED THE HELI TO BE 'FORGOTTEN.' THUS, NEITHER THE HELI, NOR MYSELF WAS INFORMED OF THE OTHER. NOTE: NORMAL PROC ON THE BRAVO RTE IS NOT TO ALLOW ANY ACFT TO ENTER UNLESS THEY HAVE OTHER ACFT 'IN SIGHT,' OR UNLESS ACFT ALREADY ON THE BRAVO RTE HAVE THE ARRIVING ACFT 'IN SIGHT.' IN HUNDREDS OF FLTS ON THE BRAVO RTE, THIS IS MY FIRST EXPERIENCE WITH SUCH A SIT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.