This maintenance procedure is believed to have led to the engine separating from the wing. The procedure was carried out because McDonnell-Douglas issued a service bulletin requiring that the "upper and lower spherical bearings that attached the pylon to the wing" (Failure Analysis, 2008, pg. 1) be replaced. Instead of carrying out the procedure according to the accompanying directions, American Airlines decided to replace the assembly via a cheaper method that involved less time and effort to undertake.
The aft bulkhead could have been brought into contact with the wing-mounted clevis via a number of different ways. Either during or after the hardware in the aft bulkhead fitting was removed, a load could have been applied that would have been sufficient enough to produce a crack. When attaching the pylon, the maintenance personnel had to be extremely careful because of the small distance between the pylon and wing attachments and the structural elements. It would only take a minor error for the forklift operator to damage the bulkhead and its upper flange (Failure Analysis, 2008).
the airlines contributed to this accident" (Failure Analysis, 2008, pg. 1).