Flight 409 was heading from Chicago to Ft. Lauderdale early Saturday morning when it happened.
One passenger shared her photos taken shortly after takeoff.
Isabel Capuano from south suburban Burnham says the plane was making a strange noise before takeoff.
After takeoff, she looked out the window and says she saw a piece of the engine fly off.
"I noticed the piece of the engine cover on the side by the wing, it was coming up," said Isabel Campuzano. "And the next thing I notice, the whole thing just tore off and flew into the air, we're leaving everything exposed. I wanted to get off of it right away."
The plane returned to O'Hare and all passengers were safely evacuated and rebooked on other flights.
Spirit Airlines says they recovered the cover for the right engine on O'Hare property and they are inspecting the aircraft.