Tragedies Made Regulators Rethink Inspection Policy

In the last decade, a half dozen structural failures on aircraft have contributed to major crashes. Two such tragedies abroad have played a key role in forcing U.S. manufacturers and federal regulators to rethink their approach to the problems of structural inspection.

They have formalized their new approach in a Supplemental Structural Inspection (SSI) program. It identifies structural components “whose failure,” according to Boeing documents, “could affect the structural integrity necessary for the safety of the airplane.” The program calls for special inspection of these components on older aircraft in the fleet.

Although Boeing says it adds less than 1% to total maintenance, the SSI program represents a substantial revision in American thinking following a 1977 crash of a Boeing 707 during a landing in Lusaka, Zambia. An acrimonious debate between British and American aviation authorities followed. The British do not believe that even the fail-safe philosophy provides sufficient redundancy in aircraft structures. A 1981 crash of a Boeing 737 in Taiwan also caused new scrutiny on the fail-safe philosophy and lent further impetus to regulations that went into effect last year calling for more detailed maintenance of airframes.

The 737 crash resulted from “. . . extensive corrosion damage in the lower fuselage structures,” according to an English transcipt of the Taiwan accident investigation board. “Rapid fracture occurred . . . resulting in rapid decompression and sudden break of passenger compartment floor beams . . . and eventual loss of power, loss of control and midair disintegration,” the report states.