Narrative:

My aircraft was taxiing to runway per ground controller instructions. As aircraft neared the approach end of the runway on taxiway C; pilot switched to tower frequency per SOP. Tower controller said; 'aircraft X; tower; on departure turn left heading 210; wind 280 at 10; runway xxl cleared for takeoff.' I immediately read back the takeoff clearance including the runway number and the turn instruction. My aircraft was about 5 sec from the hold line at the end of xxl (still taxiing when the clearance was received); and as I came up to the hold line; aircraft Y was already taking the runway from the other side. Apparently; he was taxiing for takeoff on taxiway B; and we were approaching the end of the runway at the same time. Seeing aircraft Y entering the runway; I stopped at the hold line; mildly confused. Listening to the tower transmission later; aircraft Y is heard acknowledging the takeoff clearance (though they never would have been given a turn to 210); and their transmission apparently blocked my read back. In the 1-2 seconds that were available; tower controller didn't catch it; and aircraft Y kept moving right on to the runway. Tower controller must have observed what had happened and then said; 'aircraft Y; did you copy; or; did you take that clearance; sir?' there was some confused response by the aircraft Y crew as they started their takeoff roll; having erroneously thought that the takeoff clearance was for them. Tower controller said; 'aircraft X; tower; radio check?' I responded and controller cleared me into position and hold. He then said; 'and aircraft X continue into position and hold; and did you copy the initial clearance?' I said; '...I did; and I read it back.' I then expressed surprise at seeing the aircraft Y taking the runway. Prior to clearing me for takeoff; tower called aircraft Y and said; 'aircraft Y; possible pilot deviation; I have a phone number for you to copy when you're ready...' a few seconds later; I was cleared for takeoff. Obviously; there was a similarity in flight numbers that may have led to aircraft Y thinking that the takeoff clearance given to aircraft X was for them; since we were both approaching the end of the runway at the same time.

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Original NASA ASRS Text

Title: An air carrier crew heard the takeoff clearance for a similar sounding call sign air taxi aircraft; entered the runway and departed without hesitation. The air taxi pilot recognized the air carrier crew's error and held short.

Narrative: My aircraft was taxiing to runway per Ground Controller instructions. As aircraft neared the approach end of the runway on Taxiway C; pilot switched to tower frequency per SOP. Tower controller said; 'Aircraft X; tower; on departure turn left heading 210; wind 280 at 10; Runway XXL cleared for takeoff.' I immediately read back the takeoff clearance including the runway number and the turn instruction. My aircraft was about 5 sec from the hold line at the end of XXL (still taxiing when the clearance was received); and as I came up to the hold line; Aircraft Y was already taking the runway from the other side. Apparently; he was taxiing for takeoff on Taxiway B; and we were approaching the end of the runway at the same time. Seeing Aircraft Y entering the runway; I stopped at the hold line; mildly confused. Listening to the Tower transmission later; Aircraft Y is heard acknowledging the takeoff clearance (though they never would have been given a turn to 210); and their transmission apparently blocked my read back. In the 1-2 seconds that were available; Tower Controller didn't catch it; and Aircraft Y kept moving right on to the runway. Tower Controller must have observed what had happened and then said; 'Aircraft Y; did you copy; or; did you take that clearance; sir?' There was some confused response by the Aircraft Y crew as they started their takeoff roll; having erroneously thought that the takeoff clearance was for them. Tower controller said; 'Aircraft X; Tower; radio check?' I responded and controller cleared me into position and hold. He then said; 'and Aircraft X continue into position and hold; and did you copy the initial clearance?' I said; '...I did; and I read it back.' I then expressed surprise at seeing the Aircraft Y taking the runway. Prior to clearing me for takeoff; tower called Aircraft Y and said; 'Aircraft Y; possible pilot deviation; I have a phone number for you to copy when you're ready...' a few seconds later; I was cleared for takeoff. Obviously; there was a similarity in flight numbers that may have led to Aircraft Y thinking that the takeoff clearance given to Aircraft X was for them; since we were both approaching the end of the runway at the same time.

Data retrieved from NASA's ASRS site as of April 2012 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.