Narrative:

Tower/ground controller cleared me onto the active 34 for takeoff at the same time giving me a squawk code and a change to my IFR clearance. Due to the high workload of taxiing into position and preparing for takeoff into an 800' ovc (newly instrument rated) I only read back the squawk and the IFR clearance change. I failed to read back the takeoff clearance. After running my before takeoff checklist I advanced the power and departed after liftoff the mcnary controller advised 'small aircraft X it appears that you have departed west/O a clearance.' apparently my clearance had been for position and hold rather than takeoff as I had understood. At the time of my departure mcnary was below VFR minimums and there was very little traffic in the area. I think the controllers 'rapid fire' handling of my flight would have been appropriate if he had been handling air carrier departures every 60 seconds, but was inappropriate for mi isolated departure. Although there is no excuse for departing west/O a clearance this situation could have been avoided by the following: increased alertness on my part when receiving a takeoff clearance and reading back 'cleared to takeoff' regardless of other clearance items. Change ATC's procedures to give clearance amendments to IFR departures in the runup area rather than on the runway. Change ATC's procedures to give clearance items where possible in reverse order of priority with the most important items given last. It is well known human nature that if you're going to forget something it's least likely to be the last thing you heard.

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Original NASA ASRS Text

Title: LOW TIME ISTRUCTOR PLT IS CONFUSED BY IFR CLRNC AND TAKES OFF WITHOUT CLRNC INTO IMC CONDITIONS.

Narrative: TWR/GND CTLR CLRED ME ONTO THE ACTIVE 34 FOR TKOF AT THE SAME TIME GIVING ME A SQUAWK CODE AND A CHANGE TO MY IFR CLRNC. DUE TO THE HIGH WORKLOAD OF TAXIING INTO POS AND PREPARING FOR TKOF INTO AN 800' OVC (NEWLY INSTRUMENT RATED) I ONLY READ BACK THE SQUAWK AND THE IFR CLRNC CHANGE. I FAILED TO READ BACK THE TKOF CLRNC. AFTER RUNNING MY BEFORE TKOF CHKLIST I ADVANCED THE PWR AND DEPARTED AFTER LIFTOFF THE MCNARY CTLR ADVISED 'SMA X IT APPEARS THAT YOU HAVE DEPARTED W/O A CLRNC.' APPARENTLY MY CLRNC HAD BEEN FOR POS AND HOLD RATHER THAN TKOF AS I HAD UNDERSTOOD. AT THE TIME OF MY DEP MCNARY WAS BELOW VFR MINIMUMS AND THERE WAS VERY LITTLE TFC IN THE AREA. I THINK THE CTLRS 'RAPID FIRE' HANDLING OF MY FLT WOULD HAVE BEEN APPROPRIATE IF HE HAD BEEN HANDLING AIR CARRIER DEPS EVERY 60 SECS, BUT WAS INAPPROPRIATE FOR MI ISOLATED DEP. ALTHOUGH THERE IS NO EXCUSE FOR DEPARTING W/O A CLRNC THIS SITUATION COULD HAVE BEEN AVOIDED BY THE FOLLOWING: INCREASED ALERTNESS ON MY PART WHEN RECEIVING A TKOF CLRNC AND READING BACK 'CLRED TO TKOF' REGARDLESS OF OTHER CLRNC ITEMS. CHANGE ATC'S PROCS TO GIVE CLRNC AMENDMENTS TO IFR DEPS IN THE RUNUP AREA RATHER THAN ON THE RWY. CHANGE ATC'S PROCS TO GIVE CLRNC ITEMS WHERE POSSIBLE IN REVERSE ORDER OF PRIORITY WITH THE MOST IMPORTANT ITEMS GIVEN LAST. IT IS WELL KNOWN HUMAN NATURE THAT IF YOU'RE GOING TO FORGET SOMETHING IT'S LEAST LIKELY TO BE THE LAST THING YOU HEARD.

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.