However, inspectors noted that Hill had begun to use a softer plastic bead in the stripping process, and they said studies should be conducted on whether they may not cause as much damage as harder beads used previously — and whether time restrictions on stripping should be lifted or modified.

A written response from Hill to the Morning News said that actually, several studies have already been conducted on the softer beads by the Air Force Research Lab, Battelle Memorial Institute, the Southwest Research Institute and several independent companies.

"Study results consistently show that plastic media stripping causes negligible structural damage when established procedures are followed," Hill wrote. "In all instances, fatigue crack growth rate and fatigue life cycles remain within established parameters."

Hill added that policy is still not to strip aircraft more often than once every six years, however, and personnel try to ensure that. Also, it said periodic inspections are scheduled throughout an aircraft's life cycle to look for any material failure.

"There has been no evidence of aircraft structural stress or fatigue failures caused by plastic media blasting," Hill wrote. "Plastic media stripping continues to provide a cost effective, structurally compatible aircraft paint removal process."

It also said that any bead blasting more often than every six years happens only with engineering approval. It said such extra repainting is allowed for such situations as "paint failure, too many coats of paint (which affects aircraft performance), structural modifications that require a complete strip, or special corrosion inspections."

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E-mail: lee@desnews.com