Narrative:

Approximately 20 KTS prior to V1 on takeoff roll, tower advised us to beware of wake turbulence of prior heavy departure. Then as we accelerated through V1, they continued and said that we did not have takeoff clearance. After rotation and cleanup (captain's leg), first officer told tower that we understood that we were cleared for takeoff. Tower responded that 'in the future please be careful of your takeoff clearance.' I maintained V2 +10 KTS to make sure we maintained horizontal and vertical separation with the previously departed B747. We had him both visually and on TCASII and maintained 5 mi separation. Once we got to a safe altitude and reduced workload, I queried the other 2 crew members whether or not they heard a takeoff clearance issued. They both said they did. I don't know why the discrepancy. Flight continued on to cvg without further comments from ATC and uneventfully.

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Original NASA ASRS Text

Title: DC8-73 TKOF CLRNC DISPUTED BY FLC WHO ALL BELIEVED THAT THEY HAD HEARD THE CLRNC. HOWEVER, ATCT CTLR SAID THEY DID NOT HAVE CLRNC AND ISSUED ADVISORY FOR WAKE TURB OF B747 DEPARTED AHEAD OF THEM.

Narrative: APPROX 20 KTS PRIOR TO V1 ON TKOF ROLL, TWR ADVISED US TO BEWARE OF WAKE TURB OF PRIOR HVY DEP. THEN AS WE ACCELERATED THROUGH V1, THEY CONTINUED AND SAID THAT WE DID NOT HAVE TKOF CLRNC. AFTER ROTATION AND CLEANUP (CAPT'S LEG), FO TOLD TWR THAT WE UNDERSTOOD THAT WE WERE CLRED FOR TKOF. TWR RESPONDED THAT 'IN THE FUTURE PLEASE BE CAREFUL OF YOUR TKOF CLRNC.' I MAINTAINED V2 +10 KTS TO MAKE SURE WE MAINTAINED HORIZ AND VERT SEPARATION WITH THE PREVIOUSLY DEPARTED B747. WE HAD HIM BOTH VISUALLY AND ON TCASII AND MAINTAINED 5 MI SEPARATION. ONCE WE GOT TO A SAFE ALT AND REDUCED WORKLOAD, I QUERIED THE OTHER 2 CREW MEMBERS WHETHER OR NOT THEY HEARD A TKOF CLRNC ISSUED. THEY BOTH SAID THEY DID. I DON'T KNOW WHY THE DISCREPANCY. FLT CONTINUED ON TO CVG WITHOUT FURTHER COMMENTS FROM ATC AND UNEVENTFULLY.

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.