B737-800
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Human-Machine Interface
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Procedure; Human Factors; Chart Or Publication
I was Captain and the PM (Pilot Monitoring) on this leg. SEA was a mess due to a closed runway and taxiways. We paid particular attention to the taxi out and it went perfect. We took off 34C flying the SUMMA1 Departure. Passing Summa Seattle Center cleared us to direct to KOTAA. I typed in KOTTA and went to 'PLAN' mode and had FO (First Officer) (PF [Pilot Flying]) 'verify'; which he did. I executed it and selected LNAV. We were basically heading straight to KOTTA. ATC queried us as to our heading and then cleared us to our filed route. We proceeded [to the route] and completed the flight.Event occurred because I typed in the incorrect fix and we both believed it was correct. The two fixes are KOTAA (correct fix for us) and KOTTA (incorrect fix for us but close enough to be confusing). I should have had the IFR page up with our route and all waypoints selected and cross referenced it. Additionally; the flight plan could/should have been cross referenced. We did speak up and ask for confirmation; at which time ATC just cleared us to a new fix.I will be more diligent in the future.
We were flying the SUMMA1 departure we were cleared to SUMMA; then cleared to KOTAA. The PM (Pilot Monitoring) typed it in; we verified it on the plan mode. It did not look right; started to fly toward the fix which was ahead of us. Then ATC said we looked right of course and then cleared us to [back to our route]. When we looked further into it we typed KOTTA. Instead of KOTAA. Both fixes are near each other. Incorrect fix typed very close spelling. Needed to slow down and verify. [Remember to] double check the spelling of any fix we are cleared to. Be more heads up in the future.
B737 flight crew reported a heading deviation due to similar fix names.