Narrative:

A twin cessna called ready for takeoff runway 21. I did not see a twin cessna at runway 21. I scanned and saw a twin cessna at runway 3. Aircraft had taxied out to the wrong runway. I instructed the aircraft to hold short of the runway; and she read back hold short. I had very little traffic at the time; so my plan was to depart the twin cessna off runway 3 without too much delay. Another aircraft called ready to go runway 21. I cleared the other aircraft for takeoff runway 21. As the other aircraft acknowledged takeoff clearance; he was stepped on by another aircraft. I mentioned on frequency that an aircraft was stepping on another aircraft; then made a control instruction to an aircraft in the pattern; then said 'other aircraft calling scottsdale; say again'. The twin cessna replied that she was cleared for takeoff. I immediately yelled negative! Twin cessna hold position! The twin cessna had crossed the hold lines but had stopped short of the runway edge line. I turned back to the other aircraft and he was already airborne approximately 1000 ft. Down runway 21 departure end. I sent the next aircraft on final around since the twin cessna had crossed the hold lines. I told the twin cessna that she was at the wrong runway and did not have a takeoff clearance. I then instructed the twin cessna to exit the runway and contact ground for taxi to runway 21. I probably should have told the twin cessna that she was at the wrong runway when she first called instead of just telling her to hold short. I am guessing that when she heard cleared for takeoff; she assumed she was the only one I could be clearing even though it was a completely different call sign.

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Original NASA ASRS Text

Title: Communication miscue between pilot and controller leads to two aircraft thinking they are cleared for takeoff at opposite ends of the same runway. Controller observes pending incursion and takes corrective action.

Narrative: A twin Cessna called ready for takeoff Runway 21. I did not see a twin Cessna at Runway 21. I scanned and saw a twin Cessna at Runway 3. Aircraft had taxied out to the wrong runway. I instructed the aircraft to hold short of the runway; and she read back hold short. I had very little traffic at the time; so my plan was to depart the twin Cessna off Runway 3 without too much delay. Another aircraft called ready to go Runway 21. I cleared the other aircraft for takeoff Runway 21. As the other aircraft acknowledged takeoff clearance; he was stepped on by another aircraft. I mentioned on frequency that an aircraft was stepping on another aircraft; then made a control instruction to an aircraft in the pattern; then said 'other aircraft calling Scottsdale; say again'. The twin Cessna replied that she was cleared for takeoff. I immediately yelled Negative! Twin Cessna Hold Position! The twin Cessna had crossed the hold lines but had stopped short of the runway edge line. I turned back to the other aircraft and he was already airborne approximately 1000 ft. down Runway 21 departure end. I sent the next aircraft on final around since the twin Cessna had crossed the hold lines. I told the twin Cessna that she was at the wrong runway and did not have a takeoff clearance. I then instructed the twin Cessna to exit the runway and contact ground for taxi to Runway 21. I probably should have told the twin Cessna that she was at the wrong runway when she first called instead of just telling her to hold short. I am guessing that when she heard cleared for takeoff; she assumed she was the only one I could be clearing even though it was a completely different call sign.

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.