LG35 CREW HAD RWY INCURSION WHILE TRYING TO FIND THE END OF THE RWY. THEY THEN TAKE OFF WITHOUT CLRNC; AT MDW.

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WE WERE CLRED TO RWY 22R VIA TXWY Y TO TXWY P. AFTER CLRING RWY 22L; THE TXWY P AND RWY 22R TURNS INTO A WIDE EXPANSE OF CONCRETE AND I REMEMBER THINKING THAT WE NEED TO USE THE FULL LENGTH OF RWY 22R AND LOOKING FOR A WAY TO ACCOMPLISH THAT WITHOUT BACK TAXIING. INITIALLY; I COULDN'T SEE THE TXWY ADJACENT TO THE THRESHOLD DUE TO A SNOW PILE OBSCURING IT FROM MY VIEW; SO I BACK TAXIED TO THE END OF RWY 22R AND ASKED MY COPLT TO CALL READY FOR TKOF. THE COPLT THEN MENTIONED THAT WE WERE ON THE RWY AND IMMEDIATELY CALLED THE TWR FOR TKOF CLRNC. I THOUGHT I COULD MAKE A HARD R TURN AND EXIT TO THE TXWY THEN THE CTLR CAME OVER THE RADIO AND SAID THAT WE WERE ON THE RWY; BUT SINCE WE WERE THERE; WE WERE OK. I STARTED THE TKOF ROLL AND AT APPROX 300 FT AGL THE CTLR CALLED AND ASKED WHAT HDG WE WERE GOING TO FLY SINCE WE DEPARTED WITHOUT A TKOF CLRNC. THE REAL PROB -- NOT ACTIVELY LISTENING. I WAS SO INTENT ON USING THE FULL RWY LENGTH THAT I INADVERTENTLY GOT ONTO THE RWY AND UPON REALIZING THAT MY MIND WENT INTO HIGH STRESS MODE FROM A RWY INCURSION! NOW SINCE I STILL WAS NOT ACTIVELY LISTENING AND I THINK MY MIND MAY HAVE BEEN REACTING TO THE FIRST STAGES OF STRESS -- THE ALARM STAGE (ACCORDING TO WHAT I HAVE READ SINCE THE EVENT) -- THE MIND IS NOW IN THE FLT OR FLEE MODE. PNF WAS DOING FINE UNTIL HE REALIZED THAT I HAD TAXIED ONTO THE RWY. THEN HIS COMMENT WAS THAT HE STARTED TO DAYDREAM ABOUT WHAT THE RAMIFICATIONS WERE GOING TO BE FROM THE RWY INCURSION AND HE MUST HAVE MISSED THE TKOF CLRNC. I NOW BELIEVE THAT HE WAS EXPERIENCING THE FIRST STAGES OF STRESS; TOO. SUPPLEMENTAL INFO FROM ACN 498829: I REMEMBER LOOKING BOTH WAYS XING RWY 22L; THEN I STARTED BACK ON THE CHKLIST. NEXT TIME I LOOKED OUT; WE WERE LOOKING AT THE END OF RWY 4L; JUST R OF CTRLINE. I TOLD THE CAPT WE WERE ON THE RWY. HE PAUSED; THEN ASKED FOR ME TO CALL TWR. TWR ADVISED US THAT WE WERE ALREADY ON RWY 22R; BUT GO AHEAD AND GET INTO POS AND HOLD RWY 22R. AT THAT TIME; I REMEMBER THINKING ABOUT WHAT WE JUST DID; AND HOW DID WE LET OURSELVES TAXI ONTO THE RWY. 30 SECONDS TO 1 MIN HAD PASSED IT SEEMED -- THIS IS WHERE I WAS NEEDING TO BE THINKING ABOUT THE TKOF; NOT WHAT HAD JUST HAPPENED. THE CAPT WAS BRINGING UP THE PWR. I THOUGHT I HAD MISSED THE TKOF CLRNC. WE COMMENCED A NORMAL TKOF. JUST AFTER TKOF; THE TWR ASKED US 'WHAT HDG WOULD YOU LIKE? BECAUSE YOU JUST TOOK OFF WITHOUT A TKOF CLRNC.' ONCE THE FIRST MISTAKE HAPPENS -- STOP! AND REGROUP. THIS ALL HAPPENED IN ABOUT 3 MINS.