NON TWR ARPT AND NO TXWY RESULT IN ACFT BACK TAXIING ON ACTIVE RWY ENCOUNTERING SMA BEGINNING TKOF.

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AFTER LNDG AT LHU ON RWY 5; WE EXITED THE RWY AT THE CROSS RWY 2 TO THE W AND HELD AT THIS POINT SINCE THERE IS NO TXWY BACK TO OUR GATE; WHICH IS AT THE APCH END OF RWY 5. WE HELD FOR NUMEROUS ACFT LNDG AND DEPARTING ON RWY 5. AFTER APPROX 15 MINS WE BROADCASTED ON UNICOM THAT WE WOULD BACK TAXI AFTER THE LAST ACFT HAD LANDED AND CLRED THE RWY. AS WE PULLED ONTO THE RWY WE AGAIN; BROADCASTED OUR INTENTIONS ON UNICOM. ONCE ON THE RWY I NOTICED AN SMA ALSO PULLING ONTO THE RWY AT THE APCH END OF RWY 5. THERE WAS NO READABLE XMISSION HEARD BUT A LOUD SQUEAL. AFTER A FEW SECS I NOTICED THE ACFT DEPARTING; SO I PULLED OFF THE RWY INTO THE DIRT. THE SMA DEPARTED AND TURNED SLIGHTLY AWAY FROM US. AFTER WE WERE OFF THE RWY ANOTHER DEPARTED; AND BY THIS TIME A SINGLE ENG SMA WAS ON BASE TO 5; SO WE HELD FOR THAT ACFT TO CLR AND THEN TAXIED TO OUR GATE. REASON FOR HIGH AMOUNT OF TFC ON THIS DAY WAS A FLY IN. FIVE ARPTS OPERATE UNICOM ON 122.8 IN A CLOSE VICINITY WITH HIGH AMOUNT OF WEEKEND TFC. PROB COULD HAVE BEEN CAUSED BY THE SMA'S LACK OF COM AND BY POOR JUDGEMENT OR TRNING TO ALLOW HIMSELF TO DEPART WHILE ANOTHER ACFT WAS ON THE RWY. PUT SOME OF THESE UNICOMS ON DIFFERENT FREQS AND GIVE BETTER INSTRUCTIONS ON OPERATING AT UNCTLED ARPTS.