Narrative:

Returning to the aircraft, the student called clearance delivery, got his squawk and departure control frequency, which he read back correctly. We taxied to the edge of the FBO ramp, and in conjunction with the ATIS instruction, called tower for taxi. I had the student request 'intersection juliet departure.' the student and I both heard 'back taxi runway one-seven left to intersection juliet.' the student read this instruction back. I thought it was unusual that we would be taxiing on the runway, but just then a business jet exited the runway at taxiway lima and proceeded north on taxiway bravo. I concluded that the controller was keeping us out of the jet's blast. Just prior to entering runway one-seven left (at lima), I had the urge to contact tower and verify the taxi instruction, but failed to act on this urge. The only reason I didn't was because the student and I were both sure of what we heard. As we entered one-seven left, we observed an aircraft on final (about a mile out, I would guess) for the runway. I took control of the aircraft and started a one-eighty just as the tower controller said '(a/C identification) you are entering the runway' followed by a go around instruction to the aircraft on final. After we were off the runway, I explained that we were following our taxi clearance. The tower operator denied issuing that clearance, but was cordial and said 'it turned out all right, no harm done.' I almost wish we had pulled the tapes, because I am fairly positive in what I heard, and the student concurs -- in fact, he had independently read back the same instruction. The reasons I did not ask for the tapes to be pulled were, in the first place, I had no wish for the tower controller to be 'in trouble,' and in the second place, on the off chance that both my student and I mis-heard the clearance, I thought that asking for the tapes to be pulled might be seen as a 'non-cooperating attitude,' and my exposure to sanction might be greater. In the future, I will positively question any clearance out of the ordinary.

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Original NASA ASRS Text

Title: CESSNA 150 INSTRUCTOR, WITH STUDENT, TAXIED ONTO ACTIVE RWY BELIEVING THAT THEY WERE FOLLOWING THEIR TAXI CLRNC TO BACK TAXI ON THE RWY, AND THEN OBSERVING AN ACFT ON FINAL. INSTRUCTOR TOOK ACFT CTLS TO EXIT THE RWY WHILE THE TWR SENT THE OTHER ACFT AROUND.

Narrative: RETURNING TO THE ACFT, THE STUDENT CALLED CLRNC DELIVERY, GOT HIS SQUAWK AND DEPARTURE CTL FREQUENCY, WHICH HE READ BACK CORRECTLY. WE TAXIED TO THE EDGE OF THE FBO RAMP, AND IN CONJUNCTION WITH THE ATIS INSTRUCTION, CALLED TWR FOR TAXI. I HAD THE STUDENT REQUEST 'INTERSECTION JULIET DEP.' THE STUDENT AND I BOTH HEARD 'BACK TAXI RWY ONE-SEVEN L TO INTERSECTION JULIET.' THE STUDENT READ THIS INSTRUCTION BACK. I THOUGHT IT WAS UNUSUAL THAT WE WOULD BE TAXIING ON THE RWY, BUT JUST THEN A BUSINESS JET EXITED THE RWY AT TXWY LIMA AND PROCEEDED N ON TXWY BRAVO. I CONCLUDED THAT THE CTLR WAS KEEPING US OUT OF THE JET'S BLAST. JUST PRIOR TO ENTERING RWY ONE-SEVEN L (AT LIMA), I HAD THE URGE TO CONTACT TWR AND VERIFY THE TAXI INSTRUCTION, BUT FAILED TO ACT ON THIS URGE. THE ONLY REASON I DIDN'T WAS BECAUSE THE STUDENT AND I WERE BOTH SURE OF WHAT WE HEARD. AS WE ENTERED ONE-SEVEN L, WE OBSERVED AN ACFT ON FINAL (ABOUT A MILE OUT, I WOULD GUESS) FOR THE RWY. I TOOK CTL OF THE ACFT AND STARTED A ONE-EIGHTY JUST AS THE TWR CTLR SAID '(A/C ID) YOU ARE ENTERING THE RWY' FOLLOWED BY A GAR INSTRUCTION TO THE ACFT ON FINAL. AFTER WE WERE OFF THE RWY, I EXPLAINED THAT WE WERE FOLLOWING OUR TAXI CLRNC. THE TWR OPERATOR DENIED ISSUING THAT CLRNC, BUT WAS CORDIAL AND SAID 'IT TURNED OUT ALL RIGHT, NO HARM DONE.' I ALMOST WISH WE HAD PULLED THE TAPES, BECAUSE I AM FAIRLY POSITIVE IN WHAT I HEARD, AND THE STUDENT CONCURS -- IN FACT, HE HAD INDEPENDENTLY READ BACK THE SAME INSTRUCTION. THE REASONS I DID NOT ASK FOR THE TAPES TO BE PULLED WERE, IN THE FIRST PLACE, I HAD NO WISH FOR THE TWR CTLR TO BE 'IN TROUBLE,' AND IN THE SECOND PLACE, ON THE OFF CHANCE THAT BOTH MY STUDENT AND I MIS-HEARD THE CLRNC, I THOUGHT THAT ASKING FOR THE TAPES TO BE PULLED MIGHT BE SEEN AS A 'NON-COOPERATING ATTITUDE,' AND MY EXPOSURE TO SANCTION MIGHT BE GREATER. IN THE FUTURE, I WILL POSITIVELY QUESTION ANY CLRNC OUT OF THE ORDINARY.

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.