Narrative:

I had landed at cos to let a friend off the aircraft for a visit with her family. My wife and I then continued on to apa. I had landed on runway 17R upon arrival and parked on the GA ramp. For departure I was cleared to taxi to runway 17R via taxiway a. I went to the east edge of the ramp, picked up the yellow line and taxied north. I had only landed at cos one other time -- about 12 yrs ago, and so was not familiar with the airport. Going north along the ramp I thought I was on taxiway a. At taxiway A2, I asked for an intersection takeoff. Ground control said, 'intersection takeoff approved, hold short of runway 17R at taxiway A2.' I turned east on taxiway A2 and stopped short of taxiway a, thinking I was short of runway 17R. When I received takeoff clearance, I turned onto taxiway a and made the takeoff. After I was in the air, the tower asked me to confirm that I had departed the taxiway. Factors in problem: 6000 hour pilot who thinks he is a professional, but did not take time to study the airport diagram. At A2 intersection with taxiway a I did not see a 'hold short line' of course but this did not warn me. When I turned onto taxiway a for takeoff, I should have realized there was no white line down the centerline and that there were blue lights along the edges. It all adds up to being too complacent and to not paying attention. Lucky for me there was no real problem as a result.

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Original NASA ASRS Text

Title: PLT TAKES OFF ON TXWY AT COS.

Narrative: I HAD LANDED AT COS TO LET A FRIEND OFF THE ACFT FOR A VISIT WITH HER FAMILY. MY WIFE AND I THEN CONTINUED ON TO APA. I HAD LANDED ON RWY 17R UPON ARR AND PARKED ON THE GA RAMP. FOR DEP I WAS CLRED TO TAXI TO RWY 17R VIA TXWY A. I WENT TO THE E EDGE OF THE RAMP, PICKED UP THE YELLOW LINE AND TAXIED N. I HAD ONLY LANDED AT COS ONE OTHER TIME -- ABOUT 12 YRS AGO, AND SO WAS NOT FAMILIAR WITH THE ARPT. GOING N ALONG THE RAMP I THOUGHT I WAS ON TXWY A. AT TXWY A2, I ASKED FOR AN INTXN TKOF. GND CTL SAID, 'INTXN TKOF APPROVED, HOLD SHORT OF RWY 17R AT TXWY A2.' I TURNED E ON TXWY A2 AND STOPPED SHORT OF TXWY A, THINKING I WAS SHORT OF RWY 17R. WHEN I RECEIVED TKOF CLRNC, I TURNED ONTO TXWY A AND MADE THE TKOF. AFTER I WAS IN THE AIR, THE TWR ASKED ME TO CONFIRM THAT I HAD DEPARTED THE TXWY. FACTORS IN PROB: 6000 HR PLT WHO THINKS HE IS A PROFESSIONAL, BUT DID NOT TAKE TIME TO STUDY THE ARPT DIAGRAM. AT A2 INTXN WITH TXWY A I DID NOT SEE A 'HOLD SHORT LINE' OF COURSE BUT THIS DID NOT WARN ME. WHEN I TURNED ONTO TXWY A FOR TKOF, I SHOULD HAVE REALIZED THERE WAS NO WHITE LINE DOWN THE CTRLINE AND THAT THERE WERE BLUE LIGHTS ALONG THE EDGES. IT ALL ADDS UP TO BEING TOO COMPLACENT AND TO NOT PAYING ATTN. LUCKY FOR ME THERE WAS NO REAL PROB AS A RESULT.

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.