AFTER SEVERAL ATTEMPTS TO CONTACT TTN TWR; AN SK76 CREW BELIEVED THE TWR WAS NOT OPEN AND DEPARTED USING CTAF PROCS.

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UPON TAXIING OUT FOR THE FIRST FLT OF THE DAY AT TTN; AFTER COMPLETING ALL CHKLISTS AND OBTAINING ATIS ON #2 RADIO; COPLT TRIED TO CALL TWR FREQ AS USUAL FOR TAXI AND TKOF CLRNC ON THE #1 RADIO. THERE WAS NO ANSWER TO THE FIRST 2 TRIES. COPLT RECALLS CONFIRMING FREQ AND XMISSION ANNUNCIATION ON RADIO CTL HEAD. AS IT WAS NOT LONG AFTER THE TIME THAT THE TWR IS SUPPOSED TO COMMENCE OPS; THE CREW DECIDED TO SELF ANNOUNCE INTENTIONS ON CTAF AND PROCEED TO TAXI AND TAKE OFF. THIS WAS UNDER THE ASSUMPTION THAT THE TWR WAS NOT YET OPENED AND/OR ON THE RADIO YET. THE COPLT MADE SEVERAL SELF ANNOUNCEMENTS ON CTAF DURING TAXI AND DEP. PRIOR TO TKOF; AREA WAS CLRED VISUALLY; AND WITH THE TCASII. ONE ARR FOR RWY 6 WAS SPOTTED AT WHAT APPEARED TO THE CREW TO BE AT LEAST 10 MI OUT. TKOF WAS COMPLETED IN A NORMAL MANNER FOR A HELI ON THE INTERIM 'WHISKEY' HELI ROUTING. NO COM WAS HEARD BEFORE CLRING THE FREQ FOR THE NEXT ARPT AT 7 MI FROM TTN. WE FOUND OUT THAT TWR HAD BEEN TRYING TO COM TO US WHEN OUR CHIEF PLT CALLED US ON OUR CELL PHONE 25 MINS LATER. UNTIL THAT TIME; WE WERE UNAWARE OF A PROB. AFTER FINDING OUT ABOUT THIS PROB; THE #1 RADIO WAS CHKED FOR OP AND WAS WORKING. IN HINDSIGHT; THE CREW SHOULD HAVE TRIED A DIFFERENT RADIO AND/OR GND FREQ BEFORE MOVING ON TO THE TXWY OR DEPARTING THE ARPT. ALSO; THERE WAS SOME CONFUSION ABOUT THE EXACT HRS OF TWR OP. I THINK THAT THE EARLY HR; COMPLACENCY; AND POOR JUDGEMENT ARE SOME OF THE CONTRIBUTING FACTORS TO THIS EVENT. I WILL NEVER AGAIN MOVE AT A TWRED ARPT DURING PUBLISHED OPERATING HRS UNTIL EVERY POSSIBLE FORM OF COM WITH THE TWR HAS BEEN EXHAUSTED. SUPPLEMENTAL INFO FROM ACN 575053: AFTER SEVERAL TRIES AT CONTACTING TWR AND CONFIRMING CORRECT FREQ AND RADIO XMITTING OK; I INQUIRED OF MY CAPT THE HRS OF OP OF THE TWR. WE DETERMINED THAT THE TWR MUST NOT HAVE OPENED YET. HE PROCEEDED TO TAXI TO OUR HELIPAD AND THEN TAKE OFF. I CONTINUED SELF-ANNOUNCEMENTS ON CTAF UNTIL CLRING CLASS D. IT IS CLR WE SHOULD HAVE CONFIRMED TWR'S OPERATING HRS PRIOR TO MOVING OFF OF OUR RAMP. WE SHOULD HAVE GONE TO GREATER LENGTHS TO CONFIRM CORRECT FREQ SELECTED AND RADIO ACTUALLY XMITTING. COMPLACENCY AND POOR JUDGEMENT PLAYED A MAJOR ROLE IN THIS INCIDENT. WE DID MOVE THE ACFT WITHOUT ESTABLISHING CONTACT WITH TWR.