I looked and they appear to fly three days per week on Wed/Fri/Sun starting in June. The return on Sun from FRA is at 10:30a and lands around 13:00 in STL. This is being subsidized or guaranteed profitable by quite a few businesses with ties to Europe: NestlePurina, Bayer(Monsanto), SigmaAldrich, and more.
That 13:00 arrival leaves plenty of room for Southwest connections. International arrivals are below the Southwest terminal and the StarAlliance connections would be in terminal 1 outside security and a shuttle ride away.
Last edited by equals42; Dec 28, 2021 at 8:56 pm
Reason: additional info