A C182 INSTRUCTOR; STUDENT; AND PAX STARTED TKOF ROLL AT GUC; A NON TWR ARPT; EVEN THOUGH A LCL COMMUTER HAD ANNOUNCED THEIR INTENTIONS TO USE THE OPPOSITE DIRECTION RWY.

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ANNOUNCED INTENTIONS TO DEPART RWY 6 ON CTAF 122.7 PRIOR TO TAXI TO RWY 6. WINDS AT THIS TIME FAVORED RWY 6 PER THE NEAREST WINDSOCK AND UNICOM ADVISORY. A TURBO COMMANDER HAD JUST DEPARTED AHEAD OF ACFT X ON RWY 6. WHILE ACFT X TAXIED TO RWY 6; AN ACR BEECHCRAFT 1900 ANNOUNCED INTENTION (ON 122.7) TO DEPART RWY 24. USING 122.7; ACFT X CALLED THE B1900 TO REANNOUNCE INTENTION TO USE RWY 6. THERE WAS NO RESPONSE FROM THE B1900. ACFT X THEN PERFORMED ITS RUN-UP. ACFT X ANNOUNCED ITS INTENTION TO DEPART RWY 6 AND SPECIFICALLY ASKED THE INTENTION AND POS OF THE BEECHCRAFT. NO RESPONSE WAS RECEIVED FROM THE BEECHCRAFT. WE STILL HEARD NOTHING FROM THE B1900. AT THAT TIME ACFT X MADE ANOTHER CALL ON 122.7 ANNOUNCING INTENTION TO DEPART RWY 6. NO OTHER TFC REPLIED. AT THIS TIME WE ASSUMED THAT THE B1900 WAS OFF THE UNICOM FREQ; PROBABLY GETTING IFR CLRNC. SINCE THEY WERE UNRESPONSIVE; WE FURTHER ASSUMED THEY WERE NOT MOVING OR READY TO DEPART. AFTER STOPPING AT THE DEP END OF RWY 6 AND DOING A HIGH ALT LEANING; THE BRAKES WERE RELEASED AND ACFT X STARTED ITS GND ROLL. JUST AFTER BEGINNING ITS ROLL; THE CFI IN THE R FRONT SEAT MADE THE COMMENT THAT HE THOUGHT HE SAW AN ACFT DEPARTING RWY 24. HE IMMEDIATELY TOOK CTL OF THE ACFT AND THE L SEAT PLT IMMEDIATELY RELEASED CTL TO THE CFI; WHO INITIATED AN IMMEDIATE 180 DEG TURN. THE CFI EVALUATED LEAVING THE RWY AT THAT POINT; HOWEVER; FELT THERE WAS SUFFICIENT SPACE AND TIME TO GO THE DISTANCE BACK TO THE TXWY. ACFT X EXITED ONTO THE TXWY AFTER A HIGH SPD TAXI; AT THE EXTREME R SIDE OF THE RWY. FROM THE BACK SEAT; I WAS ABLE TO WATCH THE B1900 TAKE OFF; AND KEPT OUR PLT INFORMED THAT THE B1900 WAS OFF THE GND WELL BEHIND US; AND WAS NO FACTOR FOR COLLISION. IMMEDIATELY UPON CLRING THE RWY; THE CFI CALLED ON 122.7 TO THE B1900 TO NOTIFY THEM OF THE SIT. NO RESPONSE WAS HEARD. AT ABOUT THIS TIME I OBSERVED THE B1900 FLY OVER US AT LEAST 200 FT AGL. ABOUT 15-20 SECONDS LATER; THE B1900 MADE A ROUTINE CALL ANNOUNCING 'OFF RWY 24 AT GUC.' THERE WAS NO INDICATION THAT THE B1900 HEARD OUR CALL TO THEM; OR WAS EVER AWARE OF OUR PRESENCE ON RWY 6. AFTER RECHKING FOR CONFLICTING TFC; AND MAKING THE APPROPRIATE CALLS ON 122.7; ACFT X DEPARTED RWY 6 WITH NO FURTHER INCIDENTS. CONTRIBUTING FACTORS: 1) B1900 NOT MONITORING OR TALKING ON UNICOM FREQ 122.7. 2) OUR ASSUMPTION THAT THE B1900 WAS NOT DEPARTING SINCE IT NEVER COMMUNICATED WITH GUC TFC. 3) CONSTRUCTION ON THE TXWY; REQUIRING BACK-TAXI ON THE RWY TO GO TO THE OPPOSITE END. HUMAN PERFORMANCE CONSIDERATIONS: 1) COMMUTER PLTS BEING COMPLACENT WITH OPS AT NON TWRED ARPTS. 2) OUR ASSUMPTION THAT 'AIRLINE PLTS' WOULD MAKE TFC CALLS AT NON TWRED ARPTS. 3) OUR ASSUMPTION THAT SINCE WE DIDN'T HEAR ANYTHING; THE B1900 MUST NOT BE MOVING.