The Learjet landed safely around 1:30 p.m. at STL. Passengers were seen disembarking from the plane.
The plane first reported problems near Parks Airport in Cahokia, Illinois. It circled the airport there for a while before deciding to head to Lambert Airport.
Diane Earhart of St. Louis Downtown Airport in Cahokia said Monday afternoon that air traffic control has confirmed the aircraft's landing gear is not functioning correctly. She says the pilot is circling the airport to determine when and how to land.
The plane originated at Wayne County Airport in Wooster, OH. It's owned by Aerometro LLC of Houston, Texas.
The Associated Press contributed to this report. All rights reserved.