- American Airlines DC-10 at Chicago
- Accident Overview
- Accident Board Findings
- Accident Board Recommendations
- Relevant Regulations / Policy / Background
- Prevailing Cultural / Organizational Factors
- Key Safety Issue(s)
- Safety Assumptions
- Resulting Safety Initiatives
- Airworthiness Directives (ADs) Issued
- Common Themes
- Related Accidents / Incidents
- Lessons Learned
- American Airlines DC-10 at Chicago
Prevailing Cultural / Organizational Factors
Airlines and manufacturers have historically communicated with each other regarding operational and/or maintenance difficulties. Manufacturer's service bulletins are a typical method of notifying air carriers of a need to perform specific maintenance in order to maintain the integrity of a design (usually detailing inspection processes), or to improve certain aspects of the design (periodic maintenance tasks, etc.) Further, these service bulletins may provide specific instructions for the service bulletin task or inspection, or provide references to manufacturer documents where the instructions may be found. The manufacturer generally creates the service bulletins and associated task instructions based on the manufacturer's knowledge of the design, the manufacturer's knowledge of best practices to accomplish a specific task, and a means by which to accomplish the task in the least invasive but still safest (from a design integrity standpoint) methods. The manufacturer may also make assumptions about how the task would be accomplished by a carrier, and designs accomplishment instructions based on those assumptions.
In the case of the inspections associated with the two DC-10 service bulletins, McDonnell-Douglas referred to the DC-10 Maintenance Manual, which provided specific instructions for removing and replacing the wing-mounted engines and pylons. The maintenance manual instructed that engine and pylon removal be conducted as two separate activities, and McDonnell-Douglas assumed, when creating the service bulletins, that the engine and pylon would not be removed as a single unit.
American Airlines was authorized by the FAA to perform their own maintenance, including development and approval of maintenance processes. In an effort to accomplish the inspections required by the referenced McDonnell-Douglas service bulletins in a more time-efficient manner, American Airlines developed a procedure which removed the engine and pylon as a single unit. In contrast to the DC-9, a smaller McDonnell-Douglas aircraft, an engine change took approximately four hours. On the DC-10, an engine change required approximately 24 hours. The cost associated with any work involving an engine removal and reinstallation therefore cost the airline more time and money, and kept the subject airplane out of service for a significantly longer period. This airline therefore felt a time pressure to be as efficient as possible in performing engine removals and reinstallations, and the elimination of the maintenance procedures associated with separate removal of the engine and pylon would have provided a significant time savings. American Airlines performed an evaluation of the proposed procedure, and determined that it could be accomplished efficiently and safely. The factor that was not sufficiently addressed was the intricate and precise movements of the forklift that were required to maneuver the engine/pylon assembly into position for reinstallation and the subsequent inability to thoroughly inspect the attachment fittings following the reinstallation. The damage caused during the reinstallation process was not discovered, and consequently allowed the inflight failure of the pylon, and separation from the wing.