Narrative:

Approaching 13R for takeoff; the captain 'dinged' the flight attendants (F/as) and we began to complete the before takeoff checklist. While running the checklist; the tower called us to line up and wait; while reading checklist items I responded to tower. We finished checklist; confirmed runway; cleared final and continued to taxi onto the runway. As we rounded the corner; the captain had run up the engines and applied takeoff thrust. It was at this time that I said; I don't think we have been cleared for takeoff. The captain responded with 'yes we have'; I said; 'are you sure'; and he confirmed. We continued the takeoff. This all seemed normal (expectation bias); and because the radios had been quiet; since my last transmission to tower; I immediately thought I had bumped a switch and did not hear the call. Rather than query the tower for our clearance; I checked my headset connections and communication panel setup and frequencies all the while completing an uneventful takeoff.if in doubt; confirm clearances with ATC as soon as possible and don't let what you think should be happening override the actual situation. We needed to break the chain of events and a timely radio transmission by any of the involved parties (crew; ATC) was all that was needed to stop this event. In the future; we all should attempt to eliminate the task saturation of listening and responding to three voices by calling for before takeoff checklist after hearing the F/a announcement; prioritize radio calls and query ATC when in doubt.

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Original NASA ASRS Text

Title: A First Officer reported challenging the Captain for not receiving takeoff clearance; instead; they had been instructed to Line up and wait; the Captain performed a takeoff nonetheless.

Narrative: Approaching 13R for takeoff; The Captain 'dinged' the Flight Attendants (F/As) and we began to complete the Before Takeoff Checklist. While running the checklist; the Tower called us to Line Up and Wait; while reading checklist items I responded to Tower. We finished checklist; confirmed runway; cleared final and continued to taxi onto the runway. As we rounded the corner; the Captain had run up the engines and applied takeoff thrust. It was at this time that I said; I don't think we have been cleared for takeoff. The Captain responded with 'yes we have'; I said; 'Are you sure'; and he confirmed. We continued the takeoff. This all seemed normal (expectation bias); and because the radios had been quiet; since my last transmission to Tower; I immediately thought I had bumped a switch and did not hear the call. Rather than query the Tower for our clearance; I checked my headset connections and communication panel setup and frequencies all the while completing an uneventful takeoff.If in doubt; confirm clearances with ATC as soon as possible and don't let what you think should be happening override the actual situation. We needed to break the chain of events and a timely radio transmission by any of the involved parties (Crew; ATC) was all that was needed to stop this event. In the future; we all should attempt to eliminate the task saturation of listening and responding to three voices by calling for Before Takeoff Checklist AFTER hearing the F/A announcement; prioritize radio calls and query ATC when in doubt.

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.