Pilots set down Barack Obama's campaign plane for an unscheduled landing in St. Louis earlier in the day because an emergency slide at the back of the plane deployed in flight, charter carrier Midwest Airlines announced Monday.

Pilots had landed the plane shortly after take off from Chicago after pilots noticed "controllability issues." The plane, which was also carrying Obama's national press corps, had been scheduled to go to Charlotte, N.C., where the presumptive Democratic presidential candidate was to give an address on the economy.

"While there was never an issue as to the safety of the flight, as a precautionary measure, we decided to divert the plane to Lambert-St. Louis International Airport, where it landed just before 10 a.m. CDT," reads a statement from the airline. "We are in the process of making alternative travel arrangements for Senator Obama and his campaign."

The National Transportation Safety Board said it assigned an investigator to the scene to determine why the tail cone emergency exit slide deployed. The tail cone did not separate from the airplane, the NTSB noted.

During the climb out of Chicago's Midway International Airport, the pilots of the Midwest MD80 noticed problems in controlling the aircraft's pitch -- the angle at which a plane tips forward and back. The problem was addressed by an on-board mechanic, but pilots said they were landing for safety purposes.

The pilots told passengers over the intercom that they had "full authority" of the aircraft.

Instead of talking to an audience in person in Charlotte, Obama addressed voters by phone in a 10-minute speech. He pledged to return to the state.

The touchdown was not classified as an emergency, but as an "unscheduled" landing. The pilot did not ask passengers to take the brace position, but those in the exit row had to clear a path and were asked to buckle up, which is not typical on charter flights.

Laura Brown, an FAA spokeswoman, said the plane did not declare an emergency, but simply "requested a diversion for mechanical issues they called a flight control problem," according to The Associated Press.

Once on the ground, reporters were told that they would not have to get off the plane. After a couple hours on the tarmac, however, passengers were allowed to disembark.

While ground crews were checking out the plane, Obama joked about the delay.

"So everything is fine, guys. Just thought we'd spice things up a little bit today. Don't you think?" Obama said.

Asked if he was worried, he said: "Anytime a pilot says that something's not working the way it's supposed to, then you know, you make sure you tighten your seatbelt.

"Everything seemed under control. The pilots knew what they were doing."

FOX News' Bonney Kapp contributed to this report.