Narrative:

Stx tower controller cleared us 'on to position and hold.' I repeated, 'roger, on to hold, runway 9.' after taxiing onto hold the controller began to change our departure clearance and stated, 'air carrier, after departure turn to...heading and maintain ....' the captain, after hearing 'after departure...,' pushed the throttles up to the take off EPR setting and began the takeoff roll. I heard no clearance to takeoff. The aircraft began takeoff roll and I read back the clearance, finishing with 'understand cleared for takeoff.' I received no reply from tower. The airspeed was accelerating through approximately 120 KTS (vref approximately 140 KTS) so I elected not to say anything. After becoming airborne the captain scolded me for reading back the clearance during a critical phase of flight. I replied that I didn't think we were cleared for takeoff. The captain turned to the flight engineer and asked, 'were we cleared for takeoff?' he replied, 'all I heard was the departure clearance.' my big mistake was not pulling the throttles back and tactfully telling the captain what I thought I didn't hear. Instead, I doubted myself and read back the clearance hoping to get the takeoff clearance after the readback. The flight engineer is very professional and was always in the loop. He should have done the same thing being my back-up. The tower could have prefaced the clearance with, 'air carrier, change in clearance, after departure maintain....'

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Original NASA ASRS Text

Title: LGT DEPARTS WITHOUT CLRNC FOR TKOF.

Narrative: STX TWR CTLR CLRED US 'ON TO POS AND HOLD.' I REPEATED, 'ROGER, ON TO HOLD, RWY 9.' AFTER TAXIING ONTO HOLD THE CTLR BEGAN TO CHANGE OUR DEP CLRNC AND STATED, 'ACR, AFTER DEP TURN TO...HDG AND MAINTAIN ....' THE CAPT, AFTER HEARING 'AFTER DEP...,' PUSHED THE THROTTLES UP TO THE TAKE OFF EPR SETTING AND BEGAN THE TKOF ROLL. I HEARD NO CLRNC TO TKOF. THE ACFT BEGAN TKOF ROLL AND I READ BACK THE CLRNC, FINISHING WITH 'UNDERSTAND CLRED FOR TKOF.' I RECEIVED NO REPLY FROM TWR. THE AIRSPD WAS ACCELERATING THROUGH APPROX 120 KTS (VREF APPROX 140 KTS) SO I ELECTED NOT TO SAY ANYTHING. AFTER BECOMING AIRBORNE THE CAPT SCOLDED ME FOR READING BACK THE CLRNC DURING A CRITICAL PHASE OF FLT. I REPLIED THAT I DIDN'T THINK WE WERE CLRED FOR TKOF. THE CAPT TURNED TO THE FE AND ASKED, 'WERE WE CLRED FOR TKOF?' HE REPLIED, 'ALL I HEARD WAS THE DEP CLRNC.' MY BIG MISTAKE WAS NOT PULLING THE THROTTLES BACK AND TACTFULLY TELLING THE CAPT WHAT I THOUGHT I DIDN'T HEAR. INSTEAD, I DOUBTED MYSELF AND READ BACK THE CLRNC HOPING TO GET THE TKOF CLRNC AFTER THE READBACK. THE FE IS VERY PROFESSIONAL AND WAS ALWAYS IN THE LOOP. HE SHOULD HAVE DONE THE SAME THING BEING MY BACK-UP. THE TWR COULD HAVE PREFACED THE CLRNC WITH, 'ACR, CHANGE IN CLRNC, AFTER DEP MAINTAIN....'

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.