mid-1960s, ADC was reducing its forces and on April 1, 1966, the 31st AD was reassigned and the airport was turned over to the Air Force Reserve and Iowa Air National Guard for limited military use. SUX controversy The airport designator "SUX" has been contentious, due to the name sounding identical to the slang word "sucks". Sioux City Mayor Craig Berenstein in 2002 described SUX as an "embarrassment" to the city. After petitioning the FAA for a changed airport identifier in 1998 and 2002, authorities found the alternatives offered - GWU, GYO, GYT, SGV, and GAY - to be unappealing, and elected to stay with SUX. In October 2007, airport board member Dave Bernstein proposed embracing the identifier, saying "Let's make the best of it. I think we have the opportunity to turn it into a positive," and noting "I've got buddies that I went to college with in different cities that can't even remember their own birthdays, but they all know the Sioux City designator — SUX." The airport now sells merchandise with the words "Fly SUX". Airport growth For several years the only airline service was from Northwest Airlines, commuter service on Northwest Airlink to Minneapolis–Saint Paul International Airport. In October 2007, Frontier Airlines began service with two daily flights between its Denver hub and Sioux City. The new service from Frontier quickly expanded to three daily non-stop flights to Denver and helped passenger traffic increase by over 150%. In April 2008, Frontier announced it would be ending service to Sioux City on May 12, citing economic conditions after the company filed for Chapter 11 bankruptcy. In July 2011, Delta Air Lines (who merged with Northwest in 2009) told the United States Department of Transportation that a weak economy and lower seat demand would force the company to reduce flights to several smaller communities including Sioux City unless it received assistance from the federal government. Delta said planes left Sioux Gateway with an average of only 51.4% of their seats full, so given that the company planned to remove turboprop planes and some of its 50-seat jets from service by the end of 2011 it wasn't economically viable for Delta to continue service. Of the average 75 passengers who flew the SUX-MSP route each day, only nine flew directly to the Twin Cities or to Sioux City, according to the Metropolitan Airports Commission. The majority of passengers were