Joe Rickey Hundley faces a misdemeanor simple assault charge in the February incident, and his trial is scheduled to start Thursday in federal court in Atlanta.
Authorities say Hundley used a racial slur to refer to the 19-month-old boy and then hit him under the right eye as the flight from Minneapolis began its descent to the Atlanta airport.
Hundley, who has pleaded not guilty, faces up to a year in prison if convicted. His lawyers say Hundley’s son was in a coma in Atlanta and he was flying there to decide whether to take him off life support.
Hundley lived in Idaho at the time but has since moved to North Carolina.