It involved a flight that had just taken off from Chicago's O'Hare Airport in 1979.
Memorials have been held over the years near the crash site in Des Plaines.
All 271 people on board American Airlines Flight 191 and two people on the ground were killed.
The crash happened after an engine broke loose from the plane.
It is the deadliest plane crash in American history outside of the 9/11 attacks.