The Air Force has data in 1967 indicating airframe weight problems in the C-5A aircraft's original design. These problems eventually led Lockheed, the C-5A manufacturer, to deviate from contract specifications by reducing wing material thicknesses. Not until September 1971, after accepting 40 aircraft, did the Air Force have enough test data to recognize that the C-5A wing might require major structural repair or modification. On the basis of a series of analyses, DOD eventually approved the wing modification in 1975. After this, the Air Force did not evaluate the technical feasibility of other existing lower cost options. GAO believes no other viable wing repair options remain at this time. Since early 1970, DOD has made several changes to its acquisition process which should enable it to deal more effectively in the future with problems such as those which occurred on the C-5A program.