ST. LOUIS -- The airplane carrying Democratic presidential candidate Barack Obama made a precautionary landing Monday in St. Louis after the crew had a problem keeping the nose up on takeoff from Chicago.

The plane, an MD-80 Midwest charter, struggled to keep the nose at the necessary angle as it left for Charlotte, N.C., the pilot said. Later, Midwest Airlines said the problem developed because an emergency slide located in the tail cone of the plane deployed in flight but never threatened the safety of the flight. The National Transportation Safety Board said it planned to investigate the incident.

Federal Aviation Administration spokeswoman Laura Brown said the plane did not declare an emergency but "requested a diversion for mechanical issues they called a flight control problem."

After landing, Obama read the paper in the front cabin, but ventured out briefly to chat with the press at one point.

"I just thought we'd spice things up a little bit today," Obama joked.

The Illinois senator and a small entourage eventually left the plane to wait out the maintenance at a local hotel; the North Carolina trip was postponed. But he called the Charlotte event to apologize for his absence and summarize his speech on the nation's economic woes. He expanded on that economic message later to his traveling press corps here in Missouri, a battleground state he hopes to win in the fall.

"I'm so sorry that I'm not down there," Obama said in the telephone call. "We had a little glitch in our plane." He promised to visit Charlotte soon.

Obama had two fundraisers in Atlanta scheduled for Monday evening.

Upon takeoff from Chicago, passengers had felt the plane dip briefly, causing a stomach-rolling sensation like being on a roller coaster, but the unexpected movement didn't alarm the frequent fliers on board.

Later, the pilot said, "We detected a little bit of controllability issue in terms of our ability to control the aircraft in the pitch, which is the nose up and nose down mode," His name was not released in accordance with Midwest policy.

"The autopilot and the aircraft are just fine. As we descended, whatever was inhibiting our ability has now been rectified. However, just for safety purposes we are going to be stopping in St. Louis and making sure that there's nothing binding our controls," he said.

The landing at 9:51 a.m. was normal.

Obama, his staff, the Secret Service entourage and the press sat on the plane for over an hour as it was being checked out at Lambert-St. Louis International Airport.

During his visit with reporters, Obama shook his head "no" when asked if he was worried.

"Anytime a pilot says something's not working the way it's supposed to, then you make sure you tighten your seat belt," Obama said. "Everything seemed under control. The pilots knew what they were doing."

Obama's campaign charter hasn't made a precautionary landing before.

"This is a first," he said.