PLT OF AN SMA TOOK OFF WITHOUT CLRNC DUE TO A MISUNDERSTANDING OF TWR INSTRUCTIONS.

Narrative

I HAD FILED IFR FROM LAMBERT; ST LOUIS TO ROCHESTER; MN. I WAS PARKED JUST N OF RWY 13/31 ON LAMBERT FIELD; RECEIVED MY CLRNC WHILE ON THE RAMP; AND WAS TOLD TO CONTACT GND CTL. I CONTACTED GND CTL; THEY HAD ME HOLD MOMENTARILY; THEN CLRED ME TO BACK TAXI ON RWY 31; AND REMAIN ON THEIR FREQ. I ARRIVED AT THE BEGINNING OF RWY 31; TURNED 180 DEGS AND FACED DOWN THE RWY. GND CTL IMMEDIATELY CALLED ME AND ASKED IF I WAS 'READY TO GO.' I REPLIED IN THE NEGATIVE; AND SAID I HAD TO COMPLETE MY RUN-UP FIRST. I WAS INSTRUCTED TO REMAIN ON THE GND CTL FREQ AND INFORM GND CTL WHEN I WAS 'READY TO GO.' I WAS JUST COMPLETING MY RUN-UP -- IT COULDN'T HAVE BEEN MORE THAN A MIN -- WHEN I WAS AGAIN CALLED AND ASKED IF I WAS 'READY TO GO YET.' I DETECTED A SENSE OF URGENCY IN HIS VOICE -- HE REALLY WANTED TO GET ME OUT OF THERE. I REPLIED THAT I WAS; AND HE SAID 'OK; MONITOR TWR.' GIVEN MY IMPRESSION OF HIS SENSE OF URGENCY; I INTERPRETED THIS TO MEAN THAT I WAS CLRED FOR TKOF; AND WAS TO MONITOR THE TWR FOR FURTHER INSTRUCTIONS AFTER TKOF. SO I TOOK OFF. I WAS SURPRISED WHEN THE TWR CALLED ME AS I WAS RETRACTING THE GEAR; INFORMING ME THAT I HAD NOT BEEN CLRED FOR TKOF. I APOLOGIZED; AND THERE WAS NO FURTHER CONVERSATION ABOUT IT. I COMPLETED THE IFR FLT UNEVENTFULLY; LNDG IN ROCHESTER SOME 2 HRS AND 12 MINS LATER. OBVIOUSLY; WHAT THEY MEANT BY 'MONITOR THE TWR' WAS 'DON'T CALL US; WE'LL CALL YOU AND CLR YOU FOR TKOF WHEN WE'RE READY.' I HADN'T FLOWN INTO LAMBERT FOR YRS AND WAS A STRANGER TO THE PARTICULAR PROCS THERE. ALSO; EVEN THOUGH I HAD ASSUMED A POS FOR TKOF WHICH WAS IDENTICAL TO THAT RESULTING FROM A 'TAXI INTO POS AND HOLD' I HAD NEVER BEEN ISSUED ANY HOLD INSTRUCTION. NOR DID GND SAY TO MONITOR THE TWR FOR TKOF CLRNC; OR ANYTHING LIKE THAT. THERE WAS NEVER ANY REF TO EITHER HOLDING OR TO FURTHER CLRNC. IN THESE CIRCUMSTANCES ANY REF TO EITHER OF THOSE COMMONLY UNDERSTOOD INSTRUCTIONS WOULD HAVE ALERTED ME TO THE FACT THAT I WAS NOT CLRED FOR TKOF AND AVOIDED THIS MISUNDERSTANDING.