UNAUTH TKOF BY AN EMB120 FLC AT TWF; ID.

Narrative

IT WAS THE START OF A 6 LEG DAY. AND IT WAS THE FIRST TIME I HAD FLOWN WITH THE CAPT. IT WAS DETERMINED THAT I WOULD FLY THE FIRST 2 LEGS TO TWIN FALLS; ID; AND THE RETURN LEG TO SALT LAKE CITY. FOR REASONS I COULD NOT DETERMINE; THE CAPT SEEMED RUSHED AND MISSED MULTIPLE RADIO CALLS. AFTER LNDG AT TWIN FALLS; THE CTLS WERE XFERRED TO THE CAPT AND HE ASKED FOR THE AFTER LNDG CHK. I NO SOONER LOOKED DOWN TO PERFORM THE CHK WHEN THE CAPT REALIZED WE WERE ABOUT TO GO OFF THE TXWY AND APPLIED FULL R TILLER STEERING TO AVOID GOING OFF. ONCE I REALIZED WHAT WAS HAPPENING; I COULD TELL THE CAPT HAD BEEN PREOCCUPIED WITH THE FUEL GAUGES RATHER THAN LOOKING OUTSIDE. THIS CERTAINLY FLUSTERED ME; AND SHOULD HAVE ACTED AS A RED FLAG. HOWEVER; THE REASON FOR THIS RPT OCCURRED DURING TKOF FROM TWIN FALLS. THE WIND WAS CALM AND THE CAPT WANTED TO DEPART RWY 7. USING THIS RWY REQUIRES A BACK TAXI FOR FULL LENGTH. THE TAXI OUT WAS NORMAL WITH ALL THE APPROPRIATE CHKS COMPLETED. BACK TAXIING ON THE RWY; THE CAPT ASKED ME TO PERFORM THE BEFORE TKOF CHK WHICH ENTAILS USING THE COCKPIT TO CABIN INTERPHONE TO TALK TO THE FLT ATTENDANT TO SEE IF THEY ARE READY. JUST BEFORE LEAVING COM #1 TO TALK TO THE FLT ATTENDANT; I HEARD THE CAPT TELL TWR WE WERE READY TO GO. I THEN HEARD TWR CLR US FOR TKOF AT THE END. AFTER TALKING WITH THE FLT ATTENDANT; SHE TOLD ME SHE WAS NOT READY; WHICH I THEN TOLD THE CAPT. I TOLD TWR WE WOULD PULL OFF AT THE END IN THE TURN-AROUND AREA. TWR THEN CLRED US TO REMAIN IN POS AND HOLD ON THE RWY AND ADVISE WHEN READY TO GO. I ACKNOWLEDGED THE TWR'S INSTRUCTIONS AND THE CAPT AGAIN ASKED ME TO CALL THE FLT ATTENDANT; WHICH I DID; TO FIND HER READY TO GO. I TOLD THE CAPT SHE WAS READY AND HE SAID SOMETHING TO THE EFFECT OF 'LET'S GET GOING; YOU HAVE THE FLT CTLS.' I ADVANCED THE PWR AND DEPARTED. ONCE AIRBORNE; TWR INFORMED US WE HAD NOT BEEN CLRED FOR TKOF. I ATTRIBUTE THIS BREAKDOWN IN CRM TO BEING RUSHED AND ASSUMING THE CAPT HAD RECEIVED A TKOF CLRNC WHEN HE SAID 'LET'S GET GOING; YOU HAVE THE FLT CTLS.' THE CAPT TOLD ME HE TOOK FULL RESPONSIBILITY FOR THE SIT. HOWEVER; I FEEL I SHARE THE BLAME; SINCE I KNEW I WAS OFF FREQ AT A CRUCIAL TIME AND COULD HAVE SIMPLY HAVE ASKED 'ARE WE CLRED FOR TKOF?'