Narrative:

I contacted ground control and was directed to the runup area of runway 1L at dulles. After completing runup, I contacted tower and indicated I was ready for takeoff. The tower controller cleared me for takeoff, advised me that another aircraft would be taking off at the same time on the parallel runway, and cautioned me to maintain runway heading. Tower then told an incoming aircraft that an small aircraft (me) would be departing prior to his landing. I proceeded to takeoff exactly maintaining runway heading. While climbing out the tower advised me that I had taken off while failing to receive a departure clearance. I was stunned and could only imagine that my clearance procedure with clearance delivery had not gotten into the computer successfully and I expressed the belief to the tower controller. I continue to consider this problem of what might have happened on into the flight and further theorized that due to the tower having given several directions all reflecting an immediate takeoff, I may have assumed a command 'take your position and hold' to have been 'cleared for takeoff.' if in fact the direction was 'take your position and hold,' we have a problem with what is said and what is implied. I believe the human mind will very often perceive what is indicated rather than what is said. This is a communication problem. It would be easy to prevent a recurrence of this nature by altering the sequence of directions given by ATC to ensure that the last command given be the critical immediate action communication. In my case, there was no sep of directions; all were run together in 1 stream, potentially leading to a misunderstood communication.

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Original NASA ASRS Text

Title: ACFT DEPARTED WITHOUT AN ATC TKOF CLRNC.

Narrative: I CONTACTED GND CTL AND WAS DIRECTED TO THE RUNUP AREA OF RWY 1L AT DULLES. AFTER COMPLETING RUNUP, I CONTACTED TWR AND INDICATED I WAS READY FOR TKOF. THE TWR CTLR CLRED ME FOR TKOF, ADVISED ME THAT ANOTHER ACFT WOULD BE TAKING OFF AT THE SAME TIME ON THE PARALLEL RWY, AND CAUTIONED ME TO MAINTAIN RWY HDG. TWR THEN TOLD AN INCOMING ACFT THAT AN SMA (ME) WOULD BE DEPARTING PRIOR TO HIS LNDG. I PROCEEDED TO TKOF EXACTLY MAINTAINING RWY HDG. WHILE CLBING OUT THE TWR ADVISED ME THAT I HAD TAKEN OFF WHILE FAILING TO RECEIVE A DEP CLRNC. I WAS STUNNED AND COULD ONLY IMAGINE THAT MY CLRNC PROC WITH CLRNC DELIVERY HAD NOT GOTTEN INTO THE COMPUTER SUCCESSFULLY AND I EXPRESSED THE BELIEF TO THE TWR CTLR. I CONTINUE TO CONSIDER THIS PROB OF WHAT MIGHT HAVE HAPPENED ON INTO THE FLT AND FURTHER THEORIZED THAT DUE TO THE TWR HAVING GIVEN SEVERAL DIRECTIONS ALL REFLECTING AN IMMEDIATE TKOF, I MAY HAVE ASSUMED A COMMAND 'TAKE YOUR POS AND HOLD' TO HAVE BEEN 'CLRED FOR TKOF.' IF IN FACT THE DIRECTION WAS 'TAKE YOUR POS AND HOLD,' WE HAVE A PROB WITH WHAT IS SAID AND WHAT IS IMPLIED. I BELIEVE THE HUMAN MIND WILL VERY OFTEN PERCEIVE WHAT IS INDICATED RATHER THAN WHAT IS SAID. THIS IS A COM PROB. IT WOULD BE EASY TO PREVENT A RECURRENCE OF THIS NATURE BY ALTERING THE SEQUENCE OF DIRECTIONS GIVEN BY ATC TO ENSURE THAT THE LAST COMMAND GIVEN BE THE CRITICAL IMMEDIATE ACTION COM. IN MY CASE, THERE WAS NO SEP OF DIRECTIONS; ALL WERE RUN TOGETHER IN 1 STREAM, POTENTIALLY LEADING TO A MISUNDERSTOOD COM.

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.