On May 25, 1979, American Airlines Flight 191 crashed immediately after takeoff from Chicago O'Hare Airport. Its left engine and pylon assembly swung upward over the top of the wing, severing the leading edge slat actuator hydraulic lines. The slats retracted under the aerodynamic forces, causing the left wing to stall. This, combined with asymmetric thrust due to the missing engine, caused the aircraft to rapidly roll to the left, descend, and crash, killing all 271 people on board and two on the ground.