Passengers on board a Delta flight to the Dominican Republic had to return to Minneapolis-St Paul International Airport on Monday after parts of the engine's outer casing separated from the plane.
In what must have been a horrifying sight for the Delta Flight 309's 149 passengers, the casing could be seen flapping off the engine, and one traveller managed to snap a picture.
The Boeing 737 departed at 7.10am but was back at the Minneapolis airport an hour later.
After three-hour delay, a replacement aircraft was brought into take the passengers onwards to their destination of Punta Cana.
According to Fox 9, Delta confirmed that portions of the engine cowling, the outer casing, separated, but would not speculate on the cause.
According to the Daily Mail, Ross Aimer, chief executive of Aero Consulting Experts, said: "These fellows did the right thing by immediately landing even though they knew there was no major danger.
"At that speed, sometimes that cowling - if it's not latched properly - would come apart."
Technicians are examining the aircraft.
Drunk woman diverts plane after 'making sexual advances'