McDonnell Says C-17’s Wings OK : Aerospace: It rebuts Pentagon charges that they have defects that could lead to premature cracks.

McDonnell Douglas, sharply disputing the findings of a Pentagon investigation, asserted Thursday that the wings of its C-17 cargo jet “are sound” and do not have serious defects that could lead to premature cracks.

“We have a proud lineage of building sound, strong military aircraft,” the company said in a statement. “The C-17 is living up to that reputation.”

The firm was rebutting comments by Rep. John Conyers (D-Mich.), who said that the Pentagon investigation raised flight safety questions and that the plane should be grounded until the matter is resolved. The company termed those statements “particularly offensive.”

The investigation by the Pentagon’s inspector general found that rivets installed in the wings were expanded to twice the upper limits set by the company’s own standards. The findings meant that the rivets exerted too much force against the holes into which they were inserted.

In addition, the report found that the firm had improperly installed two-piece fasteners that were responsible for at least some of the fuel leaks that plagued the first C-17 during its test flights late last year and early this year.

The McDonnell statement did not deny that the rivets had been expanded beyond the firm’s standards, as asserted in the inspector general’s report.

Rather, the firm said, “expansion of rivets increases the durability of an aircraft’s wing. The C-17 wing was designed for twice the service life of the aircraft (60,000 hours versus 30,000) independent of any expansion. Rivet expansion adds to that service life.”

The McDonnell statement said company records show that only one minor case of overexpansion of rivets occurred on a single aircraft, and in that case only 0.25% of the rivets were found to be slightly above tolerances. In this single case, the company said, it could find no detrimental effects.

The company also disputed assertions in the investigation that fuel leaks had been caused by fastener problems and that a specially built durability-test aircraft was not representative of the other C-17s.

Meanwhile, Defense Department spokesman Pete Williams said the Air Force was looking into the allegations.

“I can’t help you on specifically what the issue is with the fasteners or the rivets in the wings,” Williams said, “but, generally speaking, I think the feeling is the C-17 is moving along quite well.”

He said the Air Force expected to issue its findings by the end of the month.

McDonnell stock was down $2 a share at one point Thursday on news of the investigation. The company’s shares closed at $38.75, off $1.25, in New York Stock Exchange trading.

Jack Modzelewski, PaineWebber aerospace analyst, said the rivets appear to be a major topic now but added: “It does not look like this thing is going to add significantly to any overrun.”