Narrative:

I had taxied to runway 32R under ground control. After completing run-ups, I switched to tower frequency and waited several mins for open communication space as tower controller was very busy. I reported 'air carrier X, ready for takeoff.' controller replied instantly, 'aircraft X cleared for takeoff.' in retrospect, the reply was too quick and the number prior to 'X' may have been stepped on, but I read it as my call sign. I asked if I was cleared for takeoff, but received no reply from the controller. I then read back as, I understood, the clearance 'aircraft X cleared for takeoff, runway 32R.' there was no objection to my readback from the controller. As a life-long habit, I have never accepted a takeoff clearance without my own visual check, so as I took the runway, I did my usual s-turn to check the approach path/GS and saw aircraft #2 on about 1/2 mi final. I judged this as closer than I like, but within the band of tolerance received at this airport in the past. At other times, under similar conditions, I have been asked to 'expedite' my takeoff. After seeing the other aircraft, I was surprised I hadn't been asked to expedite, but I swept out of my 'south' check turn into an immediate takeoff. However, I got a call from the controller when I was at about 100 ft altitude saying I had been ordered to hold and informing me of the abort. I monitored the tower frequency for some time following this incident and noted another aircraft, with similar call sign was active in the pattern. In retrospect, this could have been a related factor. I called the tower controller from my destination, auw, approximately 2 hours later. She told me she had heard my request for clearance confirmation and my 'cleared for takeoff runway 32R' readback, but had not responded because she was busy with 'another situation' on down-leg of the pattern. The tower controller seemed particularly busy with very little communication time space. I had no time pressure and could have and should have waited for a second clearance. I may have become snared in the 'rush, rush' environment of the moment.

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Original NASA ASRS Text

Title: C170 PLT TAKES OFF MIC WITHOUT PROPER CLRNC.

Narrative: I HAD TAXIED TO RWY 32R UNDER GND CTL. AFTER COMPLETING RUN-UPS, I SWITCHED TO TWR FREQ AND WAITED SEVERAL MINS FOR OPEN COM SPACE AS TWR CTLR WAS VERY BUSY. I RPTED 'ACR X, READY FOR TKOF.' CTLR REPLIED INSTANTLY, 'ACFT X CLRED FOR TKOF.' IN RETROSPECT, THE REPLY WAS TOO QUICK AND THE NUMBER PRIOR TO 'X' MAY HAVE BEEN STEPPED ON, BUT I READ IT AS MY CALL SIGN. I ASKED IF I WAS CLRED FOR TKOF, BUT RECEIVED NO REPLY FROM THE CTLR. I THEN READ BACK AS, I UNDERSTOOD, THE CLRNC 'ACFT X CLRED FOR TKOF, RWY 32R.' THERE WAS NO OBJECTION TO MY READBACK FROM THE CTLR. AS A LIFE-LONG HABIT, I HAVE NEVER ACCEPTED A TKOF CLRNC WITHOUT MY OWN VISUAL CHK, SO AS I TOOK THE RWY, I DID MY USUAL S-TURN TO CHK THE APCH PATH/GS AND SAW ACFT #2 ON ABOUT 1/2 MI FINAL. I JUDGED THIS AS CLOSER THAN I LIKE, BUT WITHIN THE BAND OF TOLERANCE RECEIVED AT THIS ARPT IN THE PAST. AT OTHER TIMES, UNDER SIMILAR CONDITIONS, I HAVE BEEN ASKED TO 'EXPEDITE' MY TKOF. AFTER SEEING THE OTHER ACFT, I WAS SURPRISED I HADN'T BEEN ASKED TO EXPEDITE, BUT I SWEPT OUT OF MY 'S' CHK TURN INTO AN IMMEDIATE TKOF. HOWEVER, I GOT A CALL FROM THE CTLR WHEN I WAS AT ABOUT 100 FT ALT SAYING I HAD BEEN ORDERED TO HOLD AND INFORMING ME OF THE ABORT. I MONITORED THE TWR FREQ FOR SOME TIME FOLLOWING THIS INCIDENT AND NOTED ANOTHER ACFT, WITH SIMILAR CALL SIGN WAS ACTIVE IN THE PATTERN. IN RETROSPECT, THIS COULD HAVE BEEN A RELATED FACTOR. I CALLED THE TWR CTLR FROM MY DEST, AUW, APPROX 2 HRS LATER. SHE TOLD ME SHE HAD HEARD MY REQUEST FOR CLRNC CONFIRMATION AND MY 'CLRED FOR TKOF RWY 32R' READBACK, BUT HAD NOT RESPONDED BECAUSE SHE WAS BUSY WITH 'ANOTHER SIT' ON DOWN-LEG OF THE PATTERN. THE TWR CTLR SEEMED PARTICULARLY BUSY WITH VERY LITTLE COM TIME SPACE. I HAD NO TIME PRESSURE AND COULD HAVE AND SHOULD HAVE WAITED FOR A SECOND CLRNC. I MAY HAVE BECOME SNARED IN THE 'RUSH, RUSH' ENVIRONMENT OF THE MOMENT.

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.