Narrative:

I called bwi clearance delivery at the end of runway 22. I was to receive a full route clearance, so I called back ready to copy. I read back the clearance, except for a section I missed on the en route section and requested that section again. Clearance gave that portion again, with a reread on the transponder code. I thanked him and said good day. 3-5 mins later called departure T bwi and informed them I was off and climbing to my assigned altitude and heading, when they called back and said that I was not cleared to depart esn. I changed code to 1200 and maintained VFR over the airport (WX was 10000' scattered and 10 miles), which was not a problem to do. I did notice an aircraft on about 1 mi final on a cross runway, but it was not a factor as I was several hundred ft off the ground when I crossed the runway it was landing on. I called my intentions for departure on unicom of 122.8 and monitored said frequency. Departure said I was not cleared to takeoff. After a few mins departure came back on and gave an on-course heading and cleared me to 6000'. Nothing more was said about my actions, or the fact that I took off when they indicated that I should have not. I may have thrown off the person giving me the departure clearance by reading back a partial clearance but I did not understand that he wanted me to hold before I departed.

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Original NASA ASRS Text

Title: PLT OF SMA TWIN RECEIVED ENROUTE CLRNC AT AUX ARPT, THEN TOOK OFF WITHOUT DEP CLRNC.

Narrative: I CALLED BWI CLRNC DELIVERY AT THE END OF RWY 22. I WAS TO RECEIVE A FULL RTE CLRNC, SO I CALLED BACK READY TO COPY. I READ BACK THE CLRNC, EXCEPT FOR A SECTION I MISSED ON THE ENRTE SECTION AND REQUESTED THAT SECTION AGAIN. CLRNC GAVE THAT PORTION AGAIN, WITH A REREAD ON THE XPONDER CODE. I THANKED HIM AND SAID GOOD DAY. 3-5 MINS LATER CALLED DEP T BWI AND INFORMED THEM I WAS OFF AND CLBING TO MY ASSIGNED ALT AND HDG, WHEN THEY CALLED BACK AND SAID THAT I WAS NOT CLRED TO DEPART ESN. I CHANGED CODE TO 1200 AND MAINTAINED VFR OVER THE ARPT (WX WAS 10000' SCATTERED AND 10 MILES), WHICH WAS NOT A PROB TO DO. I DID NOTICE AN ACFT ON ABOUT 1 MI FINAL ON A CROSS RWY, BUT IT WAS NOT A FACTOR AS I WAS SEVERAL HUNDRED FT OFF THE GND WHEN I CROSSED THE RWY IT WAS LNDG ON. I CALLED MY INTENTIONS FOR DEP ON UNICOM OF 122.8 AND MONITORED SAID FREQ. DEP SAID I WAS NOT CLRED TO TKOF. AFTER A FEW MINS DEP CAME BACK ON AND GAVE AN ON-COURSE HDG AND CLRED ME TO 6000'. NOTHING MORE WAS SAID ABOUT MY ACTIONS, OR THE FACT THAT I TOOK OFF WHEN THEY INDICATED THAT I SHOULD HAVE NOT. I MAY HAVE THROWN OFF THE PERSON GIVING ME THE DEP CLRNC BY READING BACK A PARTIAL CLRNC BUT I DID NOT UNDERSTAND THAT HE WANTED ME TO HOLD BEFORE I DEPARTED.

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.