Narrative:

At columbia metropolitan airport located in columbia, sc, I was given permission to taxi to runway 5 at the intersection of taxiway F. Runway 11 was being used for departures by passenger carrying jets. I requested runway 29 but it would cause a delay for me, so the controller suggested runway 5 at taxiway F. When I approached this location I called up tower and advised him that I was ready to take off. He gave me the instruction to taxi into position and hold. I repeated taxi and hold and, as I turned onto the runway, it looked shorter than it actually is because the last part of the runway slopes down. Just as I was getting into position on the runway I made sure that the frequency was clear and quickly asked how much runway was remaining from that intersection. A few seconds went by and I heard a little distortion on the frequency but it was not recognizable as a transmission from the tower to anyone else or anyone else to the tower, I did not hear any words at all. At this point I was holding on the runway waiting to take off. A second later I heard the tower say '4000 ft' and immediately after that, 'cleared for takeoff.' he did not say my call sign, cleared for takeoff, but I assumed it was for me since he was just talking to me by answering my question and immediately saying cleared for takeoff. I took this as him reassuring me that I had adequate runway and telling me I was able to take off. I realized that there were departures on runway 29, but assumed that they were not ready for takeoff or holding in position as well. Immediately after I thought I was given the clearance to take off, I responded by saying either, cleared for takeoff and my call sign, or simply, cleared for takeoff and shortened the call sign. As soon as I made that transmission I began to accelerate and took off runway 5. The tower, at no point, came back and told me to abort takeoff or corrected me that I was not cleared to take off and that the clearance was for an airplane on runway 29. After reaching about 300-400 ft, I was more than surprised to find out that I was not supposed to take off and that the clearance was, in fact, for a different plane. I did not specifically question the controller if, in fact, I was the one who was receiving the takeoff clearance for 2 reasons: first, I was certain that it was for me since he did not use the call sign of a different plane after telling me the runway length. Secondly, I clearly responded that I was taking off and used my flight number. I, however, did not say the runway number as part of my response as I normally do. The tower explained to me that this mix-up might have been caused one of us stepping on a frequency which sounds plausible to me since I did not hear the airplane call sign before the phrase '4000 ft, cleared for takeoff.' however, there was no interruption between 4000 ft and cleared for takeoff and it seemed unlikely to me that he would say the call sign of a jet, answer my question, and go back and tell the jet to take off without specifically saying who he was talking to. I believe the problem was both on my side and the controller's. I should have specifically verified that it was I who was given the clearance for takeoff and the controller should have stopped me when I responded that I was taking off.

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Original NASA ASRS Text

Title: A C208 SINGLE PLT DEPARTED CAE WITHOUT PERMISSION.

Narrative: AT COLUMBIA METRO ARPT LOCATED IN COLUMBIA, SC, I WAS GIVEN PERMISSION TO TAXI TO RWY 5 AT THE INTXN OF TXWY F. RWY 11 WAS BEING USED FOR DEPS BY PAX CARRYING JETS. I REQUESTED RWY 29 BUT IT WOULD CAUSE A DELAY FOR ME, SO THE CTLR SUGGESTED RWY 5 AT TXWY F. WHEN I APCHED THIS LOCATION I CALLED UP TWR AND ADVISED HIM THAT I WAS READY TO TAKE OFF. HE GAVE ME THE INSTRUCTION TO TAXI INTO POS AND HOLD. I REPEATED TAXI AND HOLD AND, AS I TURNED ONTO THE RWY, IT LOOKED SHORTER THAN IT ACTUALLY IS BECAUSE THE LAST PART OF THE RWY SLOPES DOWN. JUST AS I WAS GETTING INTO POS ON THE RWY I MADE SURE THAT THE FREQ WAS CLR AND QUICKLY ASKED HOW MUCH RWY WAS REMAINING FROM THAT INTXN. A FEW SECONDS WENT BY AND I HEARD A LITTLE DISTORTION ON THE FREQ BUT IT WAS NOT RECOGNIZABLE AS A XMISSION FROM THE TWR TO ANYONE ELSE OR ANYONE ELSE TO THE TWR, I DID NOT HEAR ANY WORDS AT ALL. AT THIS POINT I WAS HOLDING ON THE RWY WAITING TO TAKE OFF. A SECOND LATER I HEARD THE TWR SAY '4000 FT' AND IMMEDIATELY AFTER THAT, 'CLRED FOR TKOF.' HE DID NOT SAY MY CALL SIGN, CLRED FOR TKOF, BUT I ASSUMED IT WAS FOR ME SINCE HE WAS JUST TALKING TO ME BY ANSWERING MY QUESTION AND IMMEDIATELY SAYING CLRED FOR TKOF. I TOOK THIS AS HIM REASSURING ME THAT I HAD ADEQUATE RWY AND TELLING ME I WAS ABLE TO TAKE OFF. I REALIZED THAT THERE WERE DEPS ON RWY 29, BUT ASSUMED THAT THEY WERE NOT READY FOR TKOF OR HOLDING IN POS AS WELL. IMMEDIATELY AFTER I THOUGHT I WAS GIVEN THE CLRNC TO TAKE OFF, I RESPONDED BY SAYING EITHER, CLRED FOR TKOF AND MY CALL SIGN, OR SIMPLY, CLRED FOR TKOF AND SHORTENED THE CALL SIGN. AS SOON AS I MADE THAT XMISSION I BEGAN TO ACCELERATE AND TOOK OFF RWY 5. THE TWR, AT NO POINT, CAME BACK AND TOLD ME TO ABORT TKOF OR CORRECTED ME THAT I WAS NOT CLRED TO TAKE OFF AND THAT THE CLRNC WAS FOR AN AIRPLANE ON RWY 29. AFTER REACHING ABOUT 300-400 FT, I WAS MORE THAN SURPRISED TO FIND OUT THAT I WAS NOT SUPPOSED TO TAKE OFF AND THAT THE CLRNC WAS, IN FACT, FOR A DIFFERENT PLANE. I DID NOT SPECIFICALLY QUESTION THE CTLR IF, IN FACT, I WAS THE ONE WHO WAS RECEIVING THE TKOF CLRNC FOR 2 REASONS: FIRST, I WAS CERTAIN THAT IT WAS FOR ME SINCE HE DID NOT USE THE CALL SIGN OF A DIFFERENT PLANE AFTER TELLING ME THE RWY LENGTH. SECONDLY, I CLRLY RESPONDED THAT I WAS TAKING OFF AND USED MY FLT NUMBER. I, HOWEVER, DID NOT SAY THE RWY NUMBER AS PART OF MY RESPONSE AS I NORMALLY DO. THE TWR EXPLAINED TO ME THAT THIS MIX-UP MIGHT HAVE BEEN CAUSED ONE OF US STEPPING ON A FREQ WHICH SOUNDS PLAUSIBLE TO ME SINCE I DID NOT HEAR THE AIRPLANE CALL SIGN BEFORE THE PHRASE '4000 FT, CLRED FOR TKOF.' HOWEVER, THERE WAS NO INTERRUPTION BTWN 4000 FT AND CLRED FOR TKOF AND IT SEEMED UNLIKELY TO ME THAT HE WOULD SAY THE CALL SIGN OF A JET, ANSWER MY QUESTION, AND GO BACK AND TELL THE JET TO TAKE OFF WITHOUT SPECIFICALLY SAYING WHO HE WAS TALKING TO. I BELIEVE THE PROB WAS BOTH ON MY SIDE AND THE CTLR'S. I SHOULD HAVE SPECIFICALLY VERIFIED THAT IT WAS I WHO WAS GIVEN THE CLRNC FOR TKOF AND THE CTLR SHOULD HAVE STOPPED ME WHEN I RESPONDED THAT I WAS TAKING OFF.

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.