Narrative:

We apparently took off runway 28R without clearance. On the ATIS; it stated tower frequency all runways 123.77. We pushed back and taxied out without any incident; all was normal. As we approached runway 28R we switched to tower frequency on 123.77. There are two tower frequencies; but they were only using 123.77 as it said on the ATIS. There were other aircraft landing on 28R as runway 28L was closed. We noticed that we couldn't hear all of the other flights that were taxiing and landing. I believe we did hear some of them; but not all. We were told to line up and wait 28R by tower and I read it back. The captain taxied us out into position. The next call we heard was fly runway heading; cleared for takeoff 28R. We transferred the controls and I took off. When we were airborne; tower contacted us and told us that we took off without a clearance; that she cleared another aircraft to takeoff on runway 21; and that we took that clearance instead. She also said that she tried to call us back many times to stop our takeoff that the clearance wasn't for us. Neither of us heard anything from the tower telling us to stop; or that we had read back someone else's clearance. Tower then gave us a phone number to call when we landed and switched us to departure. The rest of the flight went without incident.we could have verified that the takeoff clearance was for us. We could have also queried tower if they had switched tower frequencies from what was on the ATIS since we couldn't hear all of the other aircraft.

Related reports:

Google
 

Original NASA ASRS Text

Title: A Tower Controller and the two B737 pilots involved describe a takeoff without clearance from PDX. The B737 crew took the clearance for another flight and failed to respond when the Tower attempted to stop them.

Narrative: We apparently took off Runway 28R without clearance. On the ATIS; it stated TWR FREQ ALL RWYS 123.77. We pushed back and taxied out without any incident; all was normal. As we approached Runway 28R we switched to Tower frequency on 123.77. There are two Tower frequencies; but they were only using 123.77 as it said on the ATIS. There were other aircraft landing on 28R as Runway 28L was closed. We noticed that we couldn't hear all of the other flights that were taxiing and landing. I believe we did hear some of them; but not all. We were told to line up and wait 28R by Tower and I read it back. The Captain taxied us out into position. The next call we heard was fly runway heading; cleared for takeoff 28R. We transferred the controls and I took off. When we were airborne; Tower contacted us and told us that we took off without a clearance; that she cleared another aircraft to takeoff on Runway 21; and that we took that clearance instead. She also said that she tried to call us back many times to stop our takeoff that the clearance wasn't for us. Neither of us heard anything from the Tower telling us to stop; or that we had read back someone else's clearance. Tower then gave us a phone number to call when we landed and switched us to Departure. The rest of the flight went without incident.We could have verified that the takeoff clearance was for us. We could have also queried Tower if they had switched Tower frequencies from what was on the ATIS since we couldn't hear all of the other aircraft.

Data retrieved from NASA's ASRS site 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.