Narrative:

Tower cleared us to 'taxi into position and hold runway 29L, caution jetblast from the falcon that took off ahead of you.' my instrument rated student taxied on the runway and then advanced the power and began the takeoff roll. I told him that we were not cleared for takeoff, but he disagreed and said we were, and that they wouldn't have warned us of the jetblast unless we'd been cleared for takeoff. I thought I must have missed the takeoff clearance and agreed that we were cleared to take off. 3 seconds later, the tower told us to stop. I wasn't paying full attention to ATC. I was relying too much on my student. We were confused by the second part of the clearance -- the part that stated 'caution jetblast....' we usually only hear this sort of warning when we are cleared to take off. Supplemental information from acn 547066: in my mind I was cleared for takeoff. The tower told us to stop and reread our instructions. We stopped. I acknowledged his instructions. The regional jet which had landed on the parallel runway must have been cleared to cross our runway. This rj was approximately 5000 ft down the runway on a runway intersection between the 2 runways. I will mentally digest ATC instructions prior to readback from this date forward instead of simply repeating them.

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Original NASA ASRS Text

Title: A PA38 INSTRUCTOR AND STUDENT STARTED THEIR TKOF ROLL AFTER BEING CLRED INTO POS TO HOLD. TWR THEN ISSUED A CLRNC TO STOP.

Narrative: TWR CLRED US TO 'TAXI INTO POS AND HOLD RWY 29L, CAUTION JETBLAST FROM THE FALCON THAT TOOK OFF AHEAD OF YOU.' MY INST RATED STUDENT TAXIED ON THE RWY AND THEN ADVANCED THE PWR AND BEGAN THE TKOF ROLL. I TOLD HIM THAT WE WERE NOT CLRED FOR TKOF, BUT HE DISAGREED AND SAID WE WERE, AND THAT THEY WOULDN'T HAVE WARNED US OF THE JETBLAST UNLESS WE'D BEEN CLRED FOR TKOF. I THOUGHT I MUST HAVE MISSED THE TKOF CLRNC AND AGREED THAT WE WERE CLRED TO TAKE OFF. 3 SECONDS LATER, THE TWR TOLD US TO STOP. I WASN'T PAYING FULL ATTN TO ATC. I WAS RELYING TOO MUCH ON MY STUDENT. WE WERE CONFUSED BY THE SECOND PART OF THE CLRNC -- THE PART THAT STATED 'CAUTION JETBLAST....' WE USUALLY ONLY HEAR THIS SORT OF WARNING WHEN WE ARE CLRED TO TAKE OFF. SUPPLEMENTAL INFO FROM ACN 547066: IN MY MIND I WAS CLRED FOR TKOF. THE TWR TOLD US TO STOP AND REREAD OUR INSTRUCTIONS. WE STOPPED. I ACKNOWLEDGED HIS INSTRUCTIONS. THE REGIONAL JET WHICH HAD LANDED ON THE PARALLEL RWY MUST HAVE BEEN CLRED TO CROSS OUR RWY. THIS RJ WAS APPROX 5000 FT DOWN THE RWY ON A RWY INTXN BTWN THE 2 RWYS. I WILL MENTALLY DIGEST ATC INSTRUCTIONS PRIOR TO READBACK FROM THIS DATE FORWARD INSTEAD OF SIMPLY REPEATING THEM.

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.