the adoption of many of Midwest Airlines routes into the Frontier Airlines route system, the only remnant of Midwest Airlines which truly remains is the two letter IATA designator YX which has since been reassigned to Republic Airlines with the complete shut down of Midwest (Express) Airlines. Even the notion of Frontier and Midwest Routes as part of the Republic Airways Holdings System do not apply as Frontier Airlines was completely divested from Republic in 2013. References External links Midwest Air Group: about us Midwest Air Group Airline holding companies of the United States Companies based in Wisconsin Private equity portfolio companies TPG Capital companies