Narrative:

The event was a rejected takeoff initiated by me as a response to a communication we received from the sjc tower during our takeoff roll. That communication was 'aircraft X what are you doing?' while this communication was not an instruction from ATC (he did not say 'aircraft X abort' or 'aircraft X you are not cleared for takeoff'); the question itself; along with the volume and tone of the controller's voice and the timing of the transmission caused me to perceive this as a safety of flight issue and I immediately aborted the takeoff. After completing our taxi checklist and arriving at the hold short line for runway 30R; we switched to tower frequency. Tower cleared us to taxi into position and hold on runway 30R. The first officer acknowledged and I taxied into position at the very end of the runway in the displaced threshold area. Almost immediately upon reaching the position; and while the first officer was verbally completing the final before takeoff checklist items; the tower transmitted what I understood as our takeoff clearance. The first officer immediately acknowledged the tower with 'air carrier X cleared for takeoff.' since he responded to the tower transmission without any hesitation or indication of doubt; I took that as confirmation that I had indeed heard correctly and that we were cleared for takeoff. I slowly advanced the throttles to takeoff power with brakes applied; then eased off the brakes to prevent an uncomfortable 'lurch;' and we began our takeoff roll. I am not sure why I elected to do a full power run up prior to brake release. I normally only utilize this procedure in minimum runway situations. The first officer and I had previously discussed the fact that since we had 11000 ft available for the takeoff; a high speed abort could safely be accomplished here and so we briefed it as such. Maybe that influenced my choice. The point is that this whole process took 4-5 seconds to accomplish before we actually began the takeoff roll. There were no xmissions from the tower between the time the first officer read back our takeoff clearance and the 'what are you doing?' question that came well into our takeoff roll. I am not sure of our exact speed at the time as I was 'head up' looking down the runway; but I believe it was in excess of 100 KTS and may even have been near V1. Upon hearing the tower's transmission I elected to discontinue the takeoff and immediately initiated an abort procedure. I did this because the non specific nature of the transmission indicated confusion and caused serious doubt regarding the safety of continuing the takeoff. I was looking down the runway and could see no other aircraft on or near the runway. I was aware of our position on the runway and estimated around 7000 ft remaining to stop. The high speed abort option had been discussed and briefed. We were taking off to the north directly toward sfo and into very busy sfo; oak; sjc airspace with the possibility that they were not expecting us! I believed aborting the takeoff to be the safest and most prudent action to take. The rejected takeoff was smooth. Due to the significant amount of runway remaining; neither strong braking nor full thrust reverse was required. It was more like a normal after landing stop than an rejected takeoff. We turned off the runway on either taxiway H or taxiway J. During the slow down and as we turned off the runway; I didn't know what to make of the tower's call except to think that maybe we misheard or misunderstood the transmission we acknowledged as our takeoff clearance and in fact started our takeoff without proper clearance. Maybe we acknowledged a clearance meant for someone else? I expected we would be told as soon as we were on the taxiway. As we exited the runway the tower asked if we wanted to taxi back for another takeoff! We answered 'yes' and then asked if there were any issues or problems we needed to address. The tower said no and told us to contact ground for taxi back. The first officer contacted ground and the controller issued taxi instructions back to the departure end of runway 30R. Ground told us to contact tower when ready for takeoff. We accomplished the appropriate checklists during the taxi and discussed brake energy issues. Then I called ground again. When ground replied I asked again if there would be any 'ramifications' or problems for us to address. Ground said none at all. I then asked for the tower phone number to call (so that we could discuss the event later without tying up the frequency and broadcasting it to the world). Ground specifically stated that a phone call from me was not requested or necessary at all; but if I wanted to call they would provide the number. I asked for the number anyway. Ground provided it then and instructed us to call tower when ready. All the responses by sjc since the rejected takeoff were very casual and matter of fact as if nothing had happened out of the ordinary. Then; when the first officer called the tower ready for takeoff; the controller's first comment was an apology! He said either 'I'm sorry' or 'I apologize for yelling at you earlier.' by then I was totally confused as to the reason for his transmission during our takeoff. I just replied with something like 'it's ok. I'm glad you did' because I still thought maybe we started the takeoff without clearance. But I honestly don't really know the reason for the transmission.

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Original NASA ASRS Text

Title: SJC DEP ABORTED TKOF BECAUSE OF A CONFUSING ATC COMMENT; 'WHAT ARE YOU DOING?;' RECEIVED FROM THE LCL CTLR DURING TKOF ROLL.

Narrative: THE EVENT WAS A REJECTED TKOF INITIATED BY ME AS A RESPONSE TO A COM WE RECEIVED FROM THE SJC TWR DURING OUR TKOF ROLL. THAT COM WAS 'ACFT X WHAT ARE YOU DOING?' WHILE THIS COM WAS NOT AN INSTRUCTION FROM ATC (HE DID NOT SAY 'ACFT X ABORT' OR 'ACFT X YOU ARE NOT CLRED FOR TKOF'); THE QUESTION ITSELF; ALONG WITH THE VOLUME AND TONE OF THE CTLR'S VOICE AND THE TIMING OF THE XMISSION CAUSED ME TO PERCEIVE THIS AS A SAFETY OF FLT ISSUE AND I IMMEDIATELY ABORTED THE TKOF. AFTER COMPLETING OUR TAXI CHKLIST AND ARRIVING AT THE HOLD SHORT LINE FOR RWY 30R; WE SWITCHED TO TWR FREQ. TWR CLRED US TO TAXI INTO POS AND HOLD ON RWY 30R. THE FO ACKNOWLEDGED AND I TAXIED INTO POS AT THE VERY END OF THE RWY IN THE DISPLACED THRESHOLD AREA. ALMOST IMMEDIATELY UPON REACHING THE POS; AND WHILE THE FO WAS VERBALLY COMPLETING THE FINAL BEFORE TKOF CHKLIST ITEMS; THE TWR XMITTED WHAT I UNDERSTOOD AS OUR TKOF CLRNC. THE FO IMMEDIATELY ACKNOWLEDGED THE TWR WITH 'ACR X CLRED FOR TKOF.' SINCE HE RESPONDED TO THE TWR XMISSION WITHOUT ANY HESITATION OR INDICATION OF DOUBT; I TOOK THAT AS CONFIRMATION THAT I HAD INDEED HEARD CORRECTLY AND THAT WE WERE CLRED FOR TKOF. I SLOWLY ADVANCED THE THROTTLES TO TKOF PWR WITH BRAKES APPLIED; THEN EASED OFF THE BRAKES TO PREVENT AN UNCOMFORTABLE 'LURCH;' AND WE BEGAN OUR TKOF ROLL. I AM NOT SURE WHY I ELECTED TO DO A FULL PWR RUN UP PRIOR TO BRAKE RELEASE. I NORMALLY ONLY UTILIZE THIS PROC IN MINIMUM RWY SITUATIONS. THE FO AND I HAD PREVIOUSLY DISCUSSED THE FACT THAT SINCE WE HAD 11000 FT AVAILABLE FOR THE TKOF; A HIGH SPD ABORT COULD SAFELY BE ACCOMPLISHED HERE AND SO WE BRIEFED IT AS SUCH. MAYBE THAT INFLUENCED MY CHOICE. THE POINT IS THAT THIS WHOLE PROCESS TOOK 4-5 SECONDS TO ACCOMPLISH BEFORE WE ACTUALLY BEGAN THE TKOF ROLL. THERE WERE NO XMISSIONS FROM THE TWR BTWN THE TIME THE FO READ BACK OUR TKOF CLRNC AND THE 'WHAT ARE YOU DOING?' QUESTION THAT CAME WELL INTO OUR TKOF ROLL. I AM NOT SURE OF OUR EXACT SPD AT THE TIME AS I WAS 'HEAD UP' LOOKING DOWN THE RWY; BUT I BELIEVE IT WAS IN EXCESS OF 100 KTS AND MAY EVEN HAVE BEEN NEAR V1. UPON HEARING THE TWR'S XMISSION I ELECTED TO DISCONTINUE THE TKOF AND IMMEDIATELY INITIATED AN ABORT PROC. I DID THIS BECAUSE THE NON SPECIFIC NATURE OF THE XMISSION INDICATED CONFUSION AND CAUSED SERIOUS DOUBT REGARDING THE SAFETY OF CONTINUING THE TKOF. I WAS LOOKING DOWN THE RWY AND COULD SEE NO OTHER ACFT ON OR NEAR THE RWY. I WAS AWARE OF OUR POS ON THE RWY AND ESTIMATED AROUND 7000 FT REMAINING TO STOP. THE HIGH SPD ABORT OPTION HAD BEEN DISCUSSED AND BRIEFED. WE WERE TAKING OFF TO THE N DIRECTLY TOWARD SFO AND INTO VERY BUSY SFO; OAK; SJC AIRSPACE WITH THE POSSIBILITY THAT THEY WERE NOT EXPECTING US! I BELIEVED ABORTING THE TKOF TO BE THE SAFEST AND MOST PRUDENT ACTION TO TAKE. THE RTO WAS SMOOTH. DUE TO THE SIGNIFICANT AMOUNT OF RWY REMAINING; NEITHER STRONG BRAKING NOR FULL THRUST REVERSE WAS REQUIRED. IT WAS MORE LIKE A NORMAL AFTER LNDG STOP THAN AN RTO. WE TURNED OFF THE RWY ON EITHER TXWY H OR TXWY J. DURING THE SLOW DOWN AND AS WE TURNED OFF THE RWY; I DIDN'T KNOW WHAT TO MAKE OF THE TWR'S CALL EXCEPT TO THINK THAT MAYBE WE MISHEARD OR MISUNDERSTOOD THE XMISSION WE ACKNOWLEDGED AS OUR TKOF CLRNC AND IN FACT STARTED OUR TKOF WITHOUT PROPER CLRNC. MAYBE WE ACKNOWLEDGED A CLRNC MEANT FOR SOMEONE ELSE? I EXPECTED WE WOULD BE TOLD AS SOON AS WE WERE ON THE TXWY. AS WE EXITED THE RWY THE TWR ASKED IF WE WANTED TO TAXI BACK FOR ANOTHER TKOF! WE ANSWERED 'YES' AND THEN ASKED IF THERE WERE ANY ISSUES OR PROBS WE NEEDED TO ADDRESS. THE TWR SAID NO AND TOLD US TO CONTACT GND FOR TAXI BACK. THE FO CONTACTED GND AND THE CTLR ISSUED TAXI INSTRUCTIONS BACK TO THE DEP END OF RWY 30R. GND TOLD US TO CONTACT TWR WHEN READY FOR TKOF. WE ACCOMPLISHED THE APPROPRIATE CHKLISTS DURING THE TAXI AND DISCUSSED BRAKE ENERGY ISSUES. THEN I CALLED GND AGAIN. WHEN GND REPLIED I ASKED AGAIN IF THERE WOULD BE ANY 'RAMIFICATIONS' OR PROBS FOR US TO ADDRESS. GND SAID NONE AT ALL. I THEN ASKED FOR THE TWR PHONE NUMBER TO CALL (SO THAT WE COULD DISCUSS THE EVENT LATER WITHOUT TYING UP THE FREQ AND BROADCASTING IT TO THE WORLD). GND SPECIFICALLY STATED THAT A PHONE CALL FROM ME WAS NOT REQUESTED OR NECESSARY AT ALL; BUT IF I WANTED TO CALL THEY WOULD PROVIDE THE NUMBER. I ASKED FOR THE NUMBER ANYWAY. GND PROVIDED IT THEN AND INSTRUCTED US TO CALL TWR WHEN READY. ALL THE RESPONSES BY SJC SINCE THE RTO WERE VERY CASUAL AND MATTER OF FACT AS IF NOTHING HAD HAPPENED OUT OF THE ORDINARY. THEN; WHEN THE FO CALLED THE TWR READY FOR TKOF; THE CTLR'S FIRST COMMENT WAS AN APOLOGY! HE SAID EITHER 'I'M SORRY' OR 'I APOLOGIZE FOR YELLING AT YOU EARLIER.' BY THEN I WAS TOTALLY CONFUSED AS TO THE REASON FOR HIS XMISSION DURING OUR TKOF. I JUST REPLIED WITH SOMETHING LIKE 'IT'S OK. I'M GLAD YOU DID' BECAUSE I STILL THOUGHT MAYBE WE STARTED THE TKOF WITHOUT CLRNC. BUT I HONESTLY DON'T REALLY KNOW THE REASON FOR THE XMISSION.

Data retrieved from NASA's ASRS site as of January 2009 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.