B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion; Situational Awareness
Other Hearback/Readback. Similar call signs
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Human Factors
We were X5XX to ZZZ and squawking our correct transponder code; with the transponder on. Ground called us for taxi and referred to us as X6XX; we read back X5XX. The taxi instructions were then followed and we continued to Runway XX at Taxiway XX. Ground then handed us off to Tower using X6XX again. We responded that we were X5XX and switched Tower. Tower cleared us to line up and wait Runway XX at [Taxiway XX]. They used X5XX as the flight number. We lined up and waited. Tower cleared X5XX for takeoff and we proceeded to takeoff. Once airborne we were handed off to Departure where we were again referred to as X6XX. We read back X5XX. Departure then asked us to change our transponder code. We did as directed. Departure then wanted to know if we were X6XX; a 737 enroute to ZZZ2. We replied that we were X5XX; 737 enroute to ZZZ3. Departure then had us switch back to our original transponder code and cleared us direct to our departure fix. From that point on ATC called us X5XX; and the flight proceeded to ZZZ3 with out incident.
Despite multiple opportunities to redress the similar call sign problem a B737 took off with ATC still under the impression their call sign was X6XX rather than X5XX.