which would be required, and as a result it specified in its original maintenance procedures and subsequent service bulletins that the engine be separated from the pylon before the pylon is removed from the wing. While removal of the engine would not completely eliminate the possibility of imposing damage to the pylon structure, the likelihood would certainly be much less than that which existed when handling the pylon and engine as single unit. The pylon assembly without the engine weighs about 1,865 lbs and the c.g. is located approximately three feet forward of the forward bulkhead attachment points. The pylon and engine together weigh about 13,477 lbs. and the center of gravity is located about nine feet forward of the forward bulkhead attachment points. With the engine removed, the pylon can be supported relatively close to the pylon-to-wing attachment points where precise relative motion between the pylon and wing structure can be closely observed and controlled. Thus, McDonnell Douglas did not encourage removing the engine and pylon assembly as a single unit because of the risk involved in remating the combined assembly to the wing attach points. The Safety Board, therefore, is concerned with the manner in which the procedures used to comply with Service Bulletins 54-48 and 54-59 were evaluated, established, and carried out.

American Airlines is a designated alteration station, as are the other major carriers that conduct heavy maintenance programs. Fursuant to that designation and the applicable regulations, carriers are authorized to conduct major maintenance in accordance with the maintenance and inspection program established by the FAA!s Maintenance Review Board when the aircraft was introduced into service. Carriers are also authorized to conduct alterations and repairs in accordance with the procedures set forth in its maintenance manuals or established by its engineering departments. The FAA, through its principal maintenance inspectors, is responsible for Su rveillance of carriers' maintenance programs. However, this surveillance is broadly directed toward insuring that the carriers comply with the established maintenance and inspection program and that their maintenance programs, including administration, general practices, and personnel qualifications, are consistent with practices acceptable to the administrator. The FAA can review the carriers' maintenance manuals, but its formal approval is not required. Carriers are permitted to develop their own step-by-step maintenance procedures for a specific task without obtaining the approval of either the manufacturer of the aircraft or the FAA. It is not unusual for a carrier to develop procedures which deviate from