October 25, 2007 (by Lieven Dewitte) - Even though it was known years ago that the composition of some mechanical access panels made the F-22 susceptible to corrosion and changes were made to fix the problem, the design flaw reappeared.
An F/A-22 Raptor undergoing flight testing.
Now, a decade later, about two-thirds of the military's fleet of Raptors are suffering from corrosion, prompting the Air Force to speed up the timeline for bringing the aircraft through Hill Air Force Base for depot-level maintenance.
It's unclear how much the corrosion issue will cost the Air Force to fix. Brig. Gen. C.D. Moore, who is leading production and sustainment efforts for the F-22 at Ohio's Wright-Patterson Air Force Base, said the "cleanup and mitigation" of already-identified corrosion problems could cost nearly a half-million dollars in labor costs alone. Corrosively resistant replacement panels - which won't be ready to install for another six months - will cost millions more to produce and the jets will have to be brought back to Hill or another maintenance center for installation - at a cost of millions more.
Moore downplayed the cost, however, noting it would be absorbed by the "overall sustainment plan" budget - which he said exists to handle unforeseen problems with the jet.
The stealthy Raptor was conceived in the mid 1980s and designed to avoid detection by Soviet radars. But techniques that made the plane more stealthy - for instance, filling the seams of the access panels with a soft, rubbery putty - were not always best from the standpoint of corrosion control.
Even as the Soviet threat had diminished, however, the Air Force and the Lockheed Martin Aeronautics Company, the lead contractor for the F-22 program, continued to push to improve the plane's "low observable" qualities.
Alerted to concerns that the metals, paint and other materials used in and around the panels would interact in a way that would cause severe corrosion - particularly if moisture was to seep into the seams - Col. Kenneth Merchant, now a brigadier general and vice commander at Hill's Ogden Air Logistics Center, oversaw a change in design. Merchant left his assignment in 1997 believing that the problem had been addressed by a change which included switching the metal used in the panels from aluminum to titanium. The change made the Raptor, the twin engines of which produce a chest-rumbling 35,000 pounds of thrust each, negligibly heavier. It also made the aircraft slightly more vulnerable to radar.
Moore said the decision to overrule Merchant's change came over the course of several years as engineers sought to find "the right balance" between durability, performance and low radar observability. "We thought we got it right," he said. "We understood there was a corrosion risk."
The only good news is that Hill was able to stand up its depot maintenance center a year ahead of schedule to address the issue.
In all, Air Force maintainers are working on 17 access panels - as small as several inches and as large as two feet. Four of the panels on the topside of the aircraft have been found to be most susceptible to corrosion and will be replaced - at a cost of $50,000 per aircraft, not including labor.