The Mississippi River is known as the Middle Mississippi from the Upper Mississippi River's confluence with the Missouri River at St. Louis, Missouri, for 190 miles (310 km) to its confluence with the Ohio River at Cairo, Illinois. The Middle Mississippi is relatively free-flowing.
As Hopper notes, eight major U.S. airlines offer free cancellation for tickets purchased at least seven days in advance: Delta, United, US Airways, JetBlue, Southwest, Spirit, Frontier and American (in American 's case, you'll hold your ticket instead of purchasing it).
BananaStock/BananaStock/Getty Images. Passengers wishing to cancel flights before the departure date and time can do so online on Southwest's website or by calling reservations at 1-800-435-9792. If the flight has already departed, passengers can still cancel by calling the reservation department's 800 number.