The US National Transportation Safety Board is investigating why a Midwest Airlines Boeing MD-80 carrying Senator Barack Obama was forced to make an emergency landing today.

The crew of the chartered aircraft earlier today diverted to St. Louis, Missouri, during a flight from Chicago, Illinois, to Charlotte, North Carolina, due to a suspected flight control anomaly.

NTSB says preliminary information indicates the crew disconnected the autopilot during climbout from Chicago while being vectored around thunderstorms when they reportedly felt elevator control forces that were heavier than normal, prompting the decision to land in St. Louis.

Post flight inspection of the aircraft showed an in-flight deployment of the aft emergency exit slide within the tail cone.

The board says there were no injuries to the 48 passengers and crew traveling on the flight. Obama is the presumptive Democratic nominee in the presidential election.