FLC OF A B727 AND A SHORTS 360 TOOK OFF ON THE SAME RWY AT OPPOSITE ENDS NEAR THE SAME TIME. ONE WAS CLRED FOR TKOF AND THE OTHER THOUGHT HE OR SHE WAS.

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THE CHAIN OF EVENTS CONCERNING THIS NEAR DISASTER ARE PAINFULLY SIMPLE. 2 ACFT DEPARTED THE SAME RWY AT OPPOSITE ENDS. ONE OF THOSE ACFT WAS CLRED FOR TKOF AND ONE THOUGHT HE WAS BUT; BOTH ACFT READ BACK THEIR CALL SIGN AND TKOF CLRNC -- THE PROB WAS THEY WERE ON DIFFERENT FREQS AND HAD SIMILAR SOUNDING NUMBERS. I DON'T KNOW HOW CLOSE THESE 2 PLANES PASSED OR IF THEY WERE EVEN ON THE RWY AT THE SAME TIME; NO ONE WAS WATCHING. I HAD JUST ARRIVED IN THE TWR AND WAS TAKING A SEAT AT FLT DATA/CLRNC DELIVERY AND I SELECTED THE FLT DATA/CLRNC DELIVERY FREQ AND PUT IT IN THE SPEAKER. I HEARD THE LCL CTLR CLR SOMEONE FOR TKOF AND OUT OF FLT DATA/CLRNC DELIVERY SPEAKER I HEARD SOMEONE READ BACK TKOF CLRNC. I THOUGHT NOTHING OF THIS BECAUSE OCCASIONALLY PLANES ARE CLRED ON DIFFERENT FREQS WHEN POS ARE COMBINED. IT WAS ONLY AFTER THE ACFT WAS AIRBORNE; AND ASKED FOR FURTHER INSTRUCTIONS; DID I REALIZE SOMETHING TERRIBLE ALMOST HAPPENED. THE FOLLOWING IS HOW IT MAY HAVE HAPPENED. THE LATE NIGHT CTLR WAS WORKING ALL POS COMBINED IN THE TWR. OUR ATIS BROADCAST FOR LATE NIGHT CONFIGN USUALLY STATES; 'ALL TWR AND APCH OPS ARE BEING CONDUCTED ON FREQ 123.9' (APCH FREQ). IN THE MORNINGS; A REGULAR ATIS IS MADE AROUND XA53 WHICH STATES; 'IFR DEPS CONTACT CLRNC DELIVERY ON 121.65.' SO AFTER THE MORNING ATIS IS BEING BROADCAST THERE IS STILL ONLY 1 PERSON WORKING UP TO 5 FREQS. THIS IS USUALLY NOT A PROB BECAUSE TFC IS LIGHT. AT AROUND XB06 ANOTHER CTLR AND MYSELF ARRIVED IN THE TWR CAB TO RELIEVE THE LATE NIGHT CTLR AND START OUR FIRST SHIFT. ALSO DURING THIS TIME; 2 OTHER CTLRS WERE OPENING APCH CTL. APCH CTLRS RECEIVED THEIR BRIEFINGS AND APCH FREQS WERE DESELECTED. THEN THE LATE NIGHT CTLR BRIEFED THE RELIEVING LCL CTLR THEN MYSELF AT FLT DATA/CLRNC DELIVERY. DURING THE FLT DATA/CLRNC DELIVERY BRIEFING; THE LCL CTLR WAS STILL XMITTING ON CLRNC FREQ; AND HIS LAST XMISSION WAS FOR THE B727 TO DEPART RWY 23R. THE SHORTS 360 ALSO HEARD THIS AND THOUGHT THE TKOF CLRNC WAS FOR THEM. I BELIEVE HUMAN FATIGUE FACTORS ALSO PLAYED A ROLE IN THIS INCIDENT. THE PLT OF THE SHORTS 360 SEEMED TO BE TIRED AND CONFUSED FROM THE VERY BEGINNING. THE LATE NIGHT CTLR WAS ALSO VERY TIRED; JUST ENDING THE SHIFT. BECAUSE OF COMPLACENCY; LIGHT TFC; AND HURRIED BRIEFINGS; WE ALL MISSED VITAL INFO.