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$1M in F-22A damage blamed on faulty guidance

What high-tech tools and instructions were F-22A maintainers given to detect loose stealth coatings on engine inlets?

A flashlight and instructions to tap the inlet with their fingers.

An Air Combat Command accident investigation board concluded that an F-22A taking off Nov. 1 from Nellis Air Force Base, Nev., suffered more than $1 million in damage to its No. 2 engine after it sucked in a loose 6-by-8 inch section of the jet’s stealth coating.

The engine damage wasn’t noticed until after the F-22A from the 422nd Test and Evaluation Squadron landed following an otherwise uneventful training sortie, the report said.

The accident investigation board said the Air Force knew the type of coating used at the inlet had “poor” cohesive strength and could come loose. Later versions of the F-22A have an improved coating.

The technical orders for inspecting the coating called for maintainers to shine a flashlight and look for shadows caused by surface imperfections. If a problem was suspected, then a maintainer tapped his finger on the trouble spot and listened for a sound indicating a hollow space between the coating and airframe.

Board president Col. David Horton wrote that the lack of adequate tools and written guidance left the maintainers to do the best they could.

“In my opinion, maintenance personnel do not have sanctioned tools or clear technical orders guidance to identify disbonds in low observable material that cannot be visually identified,” the colonel stated. “... Nothing they did with the tools at their disposal would have reliably found the area or delamination which subsequently departed from the inlet.”

Horton praised the F119-PW-100 jet engine, noting that despite several fan blades breaking off inside the motor, there was no lost of thrust during the flight.