PLT OF C210 LANDS ON RWY AT LOM WITH PRECEDING ACFT STILL ON RWY. CITES TFC AND CTAF/UNICOM FREQ CONGESTION AND DECISION THAT CONTINUING LNDG WAS REASONABLE.

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I WAS APCHING LOM FROM THE SE LISTENING ON UNICOM. THERE WERE THREE PLANES IN THE PATTERN USING RWY 24 AND I ANNOUNCED THAT I WAS S OF THE FIELD AND WOULD BE ENTERING A 45 L DOWNWIND FOR RWY 24. A 172 ANNOUNCED THAT THEY WERE L CROSSWIND FOR RWY 24 AND NUMBER 3 TO LAND. I ACQUIRED THAT PLANE VISUALLY AND ANNOUNCED THAT I HAD THEM IN SIGHT AND WOULD FOLLOW AS NUMBER 4. ALL RADIO COMS WERE SUFFERING FROM OVER-TALK AS THERE ARE 3 ARPTS IN THE GENERAL AREA USING THE SAME UNICOM FREQ. JUST BEFORE TURNING DOWNWIND; I SAW A SECOND 172 TRAILING THE ONE I HAD ALREADY SEEN. I ANNOUNCED THAT I SAW THE SECOND 172 AND THAT I WOULD DO A R 360 DEG ON THE 45 AND FOLLOW THAT ACFT AS NUMBER 5. THE FIRST 172 LANDED AND PULLED OFF AT THE SECOND TXWY AND THE 172 IMMEDIATELY IN FRONT OF MY ACFT TOUCHED DOWN AROUND THE NUMBERS WHILE I WAS ON ABOUT 3/4 MILE FINAL. THE FIRST 172 STOPPED AT THE TXWY INTXN AND THE SECOND 172 APPEARED TO SLOW THEIR TAXI WAITING FOR THE PRECEDING PLANE TO CLEAR THE TXWY. AS I APCHED A SHORT FINAL; THE FIRST 172 RESUMED TAXIING AND THE SECOND 172 CONTINUED TO TAXI TOWARDS THE SECOND TXWY EXIT WHICH IS ABOUT 1800 FT DOWN THE RWY. AT THAT POINT I ELECTED TO TOUCHDOWN RATHER THAN EXECUTE A MISSED APCH AS I FELT CERTAIN OF A) MY ABILITY TO STOP IF NECESSARY OR B) MY ABILITY TO GO AROUND THE 172 ON THE GRASS IF NECESSARY. I BASED MY DECISION ON THE NUMBER OF PLANES IN THE PATTERN AND MY LACK OF AWARENESS OF THEIR SPECIFIC LOCATION AND ON THE JAMMED RADIO FREQ WHICH MIGHT PREVENT OTHER PLANES FROM HEARING A MISSED APCH ANNOUNCEMENT. THE OTHER 172 CONTINUED AND EXITED THE RAMP; BUT BOTH PLANES WERE SIMULTANEOUSLY ON THE RWY FOR ABOUT 10 SECONDS. THE CLOSEST APCH OF THE TWO ACFT WAS APPROX 1000 FT. CORRECTIVE ACTIONS: I COULD HAVE FLOWN A LONGER DOWNWIND TO AVOID ANY POTENTIAL LNDG DELAYS; MY REASON FOR NOT DOING SO WAS THE POSSIBILITY THAT THERE WAS AN ACFT BEHIND ME WHICH I HAD NOT IDENTIFIED AND WHICH MAY NOT HAVE HEARD MY CALL. AN EXTENDED DOWNWIND COULD HAVE RESULTED IN BOTH PLANES TURNING FINAL AT THE SAME TIME. A MAJOR CONTRIBUTING FACTOR WAS THE AMOUNT OF PLANES TRYING TO USE THE FREQ FROM 3 DIFFERENT ARPTS RESULTING IN RADIO BLOCKAGE AND CONFUSION AS PLTS ONLY HEARD PARTIAL CALLS AND MISTOOK THE ARPT BEING REFERENCED. ADDITIONAL UNICOM FREQS AND LIMITING THE NUMBER OF ARPTS ON THE SAME FREQ WITHIN GEOGRAPHICAL PROXIMITY WOULD HELP DEAL WITH THE COM ISSUES. CONTINUED PLT TRAINING ON CONCISE BUT BRIEF RPTING WOULD ALSO HELP WITH THE PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR POINTED OUT THERE ARE FIVE ARPTS IN THE VICINITY JUST TO THE N OF PHL WHO SHARE THE SAME CTAF/UNICOM FREQ: N31; N67; N70; N99 AND N87. ON THE PRETTY WEEKEND DATE OF THIS EVENT ALL WERE BUSY AND THE PROLIFERATION OF TFC POSITION UPDATES BY PLTS WAS SO GREAT THAT MANY WERE BLOCKED AND OTHERS WERE UNIDENTIFIABLE AS TO ORIGIN.