Delta Air Lines also built up a hub operation at DFW, which occupied most of Terminal 4E through the 1990s. The Delta hub peaked around 1991, when Delta had a 35% market share at DFW; its share was halved by 2004, after many of its mainline routes were downgraded to more frequent regional jet service in 2003. Delta constructed an satellite terminal in Terminal E in 1988 to accommodate their hub, which was permanently reopened in May 2019 for American Eagle operations. Delta closed its DFW hub in 2004 in a restructuring of the airline to avoid bankruptcy, cutting its DFW operation to only 21 flights a day from over 250 and redeploying aircraft to hubs in Cincinnati, Atlanta and Salt Lake City. Prior to the closure, Delta had a 17.3% market share at DFW.