Lockheed Martin Potentially Mixed Up Structural Fasteners in Most F-35s (excerpt)
(Source: Air Force Magazine; posted Jan. 30, 2020)
By John A. Tirpak
“All aircraft produced prior to discovery of this [problem] have titanium fasteners incorrectly installed in locations where the design calls for Inconel,” the F-35 Joint Program Office said in an email in response to a query from Air Force Magazine. “Because of this, the engineering safety analysis of the issue has assumed that each critical F-35 joint was assembled with the incorrect fasteners.”
Inconel is an alloy of nickel and chromium, and is supposed to be used in places where greater strength and corrosion resistance are required, while the titanium bolts are used in areas where its strength and lightness helps reduce weight. Titanium, however, has a lower shear strength than Inconel.
Both fasteners are called “eddie bolts” and are similar in appearance except for a number stamped on them. The titanium bolts cost about $5 apiece, while the Inconel parts cost about $20 each. A Lockheed spokeswoman said the two parts are “very difficult to distinguish, visually.”
The Lockheed spokesman said an initial analysis concluded that “titanium has sufficient strength in locations that called for Inconel eddie bolts.” Another Lockheed official said components are built with “twice the strength specified,” but he did not specify whether this was the case with the titanium eddie bolts.
The JPO said analysis as of Jan. 9 concluded “that no aircraft operating restrictions or inspections are necessary at this time.” It added that “the JPO will release a fleet guidance report” at the conclusion of the Root Cause and Corrective Action (RCCA) analysis, now being performed by Lockheed. The DCMA said it and the JPO are supervising Lockheed’s analysis to ensure it is performed without bias. (end of excerpt)
Click here for the full story, on the Air Force Magazine website.
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