In any case, AAR says, its maintenance did not cause the US Airways incident. "It is our understanding that the NTSB believes the cause of the US Air incident that apparently gave rise to this notice was stress corrosion unrelated to paint on the landing gear truck beam," the company said.

A person familiar with the procedure questioned that explanation. Within the horizontal bar of the truck beam is a drain hole, which allows water to leak out. When AAR applied the enamel coating, "they put the coating in so heavily that it blocked the drain hole," said the person, who asked that his name not be used. Blocking the drain would allow moisture to build, which would lead to corrosion, which could cause the gear to collapse, the person said.

AAR said, however, that "the paint that is applied to the internal bore of the truck beam does not even extend to the area where the drain hole is located."

Meanwhile, Goglia said the Boeing ruling does not excuse the company. "They failed to follow published procedures to repair the part, so it was not legal to install the part on an airplane," he said. "If they get approval to do alternate means, that's fine, but they are supposed to get it before they do the work."

As the broader market climbed Tuesday, shares of Boeing and US Airways also rose, 1.5% and 8%, respectively.

If you liked this article you might like

United Airlines Might Be Having an Identity Crisis That Is Worrying Wall Street

American, Spirit and United Get Downgrades as Ticket Pricing War Rages

Woman Sues Delta for Nearly $10,000 After Chomping on a Rock

Delta and American Seem to Think the Worst Is Over for Airline Stock Prices

Hurricane Irma Downgraded but Impact on Atlanta, Charlotte, Miami Hubs Lingers