A Shuttle America plan operating as United Express was diverted to Chicago Thursday for a mechanical issue.
Airline spokesman Peter Kowalchuk said Flight 3578 was traveling from Denver to Toronto when the issue occurred.
The plane landed at O'Hare International Airport without incident, Kowalchuk said, and its 68 passengers and four crew members deplaned safely.
The passengers continued on to Toronto on another plane.
It's not clear what caused the mechanical issue.