B737 CREW TOOK OFF WITHOUT CLRNC.

Narrative

WE WERE #1 FOR TKOF ON TXWY B RWY 16L AT SEA. WE WERE CLRED FOR TKOF FROM TXWY B. THE CAPT ASKED ME TO ASK FOR AN EARLY L TURN AFTER TKOF TO AVOID WX ON THE DEP PATH OF RWY 16L. I RESPONDED 'ACR ABCD CLRED FOR TKOF RWY 16L AND WOULD LIKE AN EARLY TURN TO THE L TO AVOID WX.' THE CAPT ASKED FOR THE FINAL ITEMS ON THE BEFORE TKOF CHKLIST. THEN THE CAPT BEGAN THE TKOF ROLL. AT ABOUT 60-80 KTS; THE OBSERVER (JUMP SEATER) WHO WAS FROM THE EQUIP INDUSTRY THAT HAD AUTH FROM FLT MGMNT; SAID WE WERE NOT CLRED FOR TKOF. AT THAT POINT I ASKED 'ACR ABCD CLRED FOR TKOF' AND THERE WAS NO RESPONSE. THE CAPT ELECTED TO CONTINUE THE TKOF ROLL. THE CAPT ASKED ME IF I HEARD 'CLR FOR TKOF' AND WE BOTH AGREED THAT WE HAD A TKOF CLRNC. AFTER TKOF; THE TWR CAME BACK AND SAID WE WERE NOT CLRED FOR TKOF. WE DISCUSSED THIS WITH THE OBSERVER AND HE HEARD 'CLRED FOR TKOF' AND THEN SHORTLY AFTER 'TAXI IN POS AND HOLD.' WE FEEL THIS WOULD HAVE BEEN AVOIDED IF THE TWR WOULD HAVE STATED 'ACR ABCD CANCEL TKOF CLRNC.' WHEN YOU HEAR POS AND HOLD AFTER BEING CLRED FOR TKOF; ONE ASSUMES IT IS FOR THE ACFT BEHIND YOU.