The pylon was damaged due to an incorrectly executed engine removal procedure. The correct procedure called for removal of the engine prior to the removal of the engine pylon. To save time and costs, American Airlines instructed its mechanics to remove the engine together with the pylon all at one time. A large fork lift was used to hold the engine up while it was detached from the wing. During the procedure a crew shift change occurred, leaving the fork lift unmonitored for a period of time. A problem in the fork lift's hydraulic system caused it to tilt the engine while still under the wing. This exerted enough pressure on the engine pylon to create a large indentation and a serious fracture in its body. The fracture went unnoticed for several flights, getting worse with each flight that the plane had taken. During flight 191's takeoff, enough force was generated to finally cause the pylon to fail. With the failure of the rear pylon, the left engine detached from under the wing and tore away. With the loss of the engine and the position of the slats, the plane was destined for disaster. The NTSB concluded that given the circumstances of the situation, the pilots were not in any way to blame for the resulting accident.