—Michael C. Sirak
May 16, 2008—The 341 Bulkhead is located exactly 341.80 inches from the forward tip of the F-16 Block 40/42 fighter aircraft in the center fuselage area. While inconspicuous to the outside observer, this single-piece aluminum alloy structure is fighting a battle of age that epitomizes the challenges facing USAF’s older inventory. And upon this battle weighs much—literally—since it is the primary attach point for the aircraft’s main landing gear.
Already the Air Force has discovered cracks in these bulkheads in 63 of its 397 F-16 Block 40/42s. The cracks were first discovered in the fall of 2007, officials from Hill AFB, Utah, home of Ogden Air Logistics Center, the depot that services the F-16, told the Daily Report. While this is not a safety-of-flight issue since previous modifications to the aircraft have added residual strength in this area, four of these aircraft were grounded for a while until receiving new bulkheads, the officials said. And while the remaining 59 currently operate under “no flight restrictions” due to the cracks, USAF is not flying some of them to avoid the expense of additional structural damage prior to instituting a repair.
The issue likely will not go away as other F-16 Block 40/42s may eventually show the same signs of wear and tear. It’s a fact of life that, over time, repeated stress cycles will cause the bulkhead to fatigue and crack in specific locations. The first Block 40 unit became operational in 1989, according to USAF’s F-16 fact sheet. Like USAF’s other platforms, they have been used extensively since 1990 in continual overseas deployments in places like the Middle East, Balkans, and Near East.
USAF’s newer F-16 Block 50/52 aircraft have the same bulkhead design as the Block 40/42 models and, accordingly, “will have 341 bulkhead cracks due to fatigue at some point in their service life,” the Hill officials said.
For now, the Block 40/42 airframes in question will require either a bulkhead fix or a completely new bulkhead, depending on the severity of the cracks, the officials said. The Air Force is inspecting these aircraft every 10 flight hours to closely monitor the situation.
Already the Air Force and Lockheed Martin, the aircraft’s manufacturer, have designed both the fix and the new bulkhead, which is made to handle greater stresses in the areas where cracks have been appearing in the existing model. For those aircraft with very small bulkhead cracks (i.e., less than one-quarter inch), the bulkhead fix should resolve the issue permanently. For aircraft with more pronounced cracks or more severe mission requirements, the repair will only add one-to-three years of additional service life before a bulkhead replacement is required, according to the Hill officials.
The current plan is to have depot field teams deploy to install the repair kits and then replace the bulkheads at scheduled depot intervals where necessary, the officials said. Bulkhead repairs will begin this month (May), with all temporary repairs done by January 2009 on those aircraft already identified with the cracks. Bulkhead replacements will continue through December 2009.
The Hill officials said the ongoing inspections are meant to catch future cracking early enough to allow installation of a permanent repair and greatly reduce the need for additional bulkhead replacements.
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