Are there any airports that do not have an IATA code but have a huge number of traffic?
According to this thread, pretty much anything with scheduled air service will have an IATA code to facilitate booking.
From looking at the FAA data, it looks like everything with more than 10,000 enplanements (enplanement=1 passenger boards an aircraft) is considered a &quot;primary&quot; airport, and they all have an IATA code unless the airport is strictly general aviation and unscheduled service.
For these reasons, you probably won't find anything with &quot;huge&quot; passenger traffic but no IATA code. There may be airports with unscheduled service to major hubs, though.