WASHINGTON (CNN) -- Control tower tapes reveal that the pilot of presidential hopeful Barack Obama's plane told air traffic controllers there was an emergency when he made an unscheduled landing last month in St. Louis, Missouri.

Barack Obama's plane had to make an unscheduled landing on July 7 in St. Louis, Missouri.

On July 7 the Midwest Airlines MD-81 made an unscheduled landing during the flight from Chicago, Illinois, to Charlotte, North Carolina. The owner of the plane initially said the landing was not caused by an emergency.

However the tapes, released to ABC News through a Freedom of Information Act request, contradict that report. ABC first reported on the tapes on Thursday.

Federal Aviation Administration spokeswoman Laura Brown told CNN Thursday evening that preliminary information for incidents is often incomplete or incorrect. Watch what the tapes revealed »

According to the tapes, the pilot told an FAA air traffic controller that he had limited ability to move the plane's nose up and down.

"We have limited pitch authority at flight levels; we're descending to see if we can regain pitch authority," the pilot told the air traffic controller.

"At this time we would like to declare this an emergency and also have CFR (fire and rescue equipment) standing by in St. Louis," the pilot said. The pilot remained calm throughout the recording.

Midwest Airlines acknowledged at the time that the pilot had detected a control problem in the pitch of the plane after an emergency evacuation chute opened in the aircraft's tail cone while in flight. Normally, the chute deploys only after landing and after the tail cone pops off.

The pitch, or angle of the nose of an airplane, affects the pilot's ability to control the plane.

The airline said the pilot had "full authority of the aircraft."

According to the tapes, the pilot said he regained control as the plane began to descend into St. Louis.

"We had a pitch authority problem, now that we have come down to a lower altitude it seems to have rectified itself. We do have pitch control of the aircraft at this time," he said.

Fire trucks met the aircraft when it landed at Lambert-St. Louis International Airport.

After the plane landed, Obama told reporters the plane landed because of a mechanical problem and noted it marked the first time he had had to do so.

"Just thought we'd spice things up a little bit today," he joked. "Anytime a pilot says that something's not working the way its supposed to, then, you know, you make sure you tighten your seat belt. Everything seemed under control, the pilots knew what they were doing."

The National Transportation Safety Board, which is investigating the incident, said last month that there was no evidence of tampering.

An "examination of the hardware did not reveal any evidence of missing components, nor any evidence of tampering," the board said.

CNN's Jeanne Meserve and Mike Ahlers contributed to this report.

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