Global Fastener News

Hundreds of F-35s could have the wrong fasteners in “critical areas,” according to the Defense Contract Management Agency. But F-35 builder Lockheed Martin says the problem may not need to be fixed, Air Force Magazine reports.

“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 told AFM. “Because of this, the engineering safety analysis of the issue has assumed that each critical F-35 joint was assembled with the incorrect fasteners.” 

Both fasteners are called “eddie bolts” and are similar in appearance except for a number stamped on them, AFM reports. The titanium bolts cost about $5 apiece and are lighter but have a lower sheer strength than the Inconel alloy bolts (nickel and chromium), which cost $20 each and have greater strength and corrosion resistance.

An initial analysis concluded that “titanium has sufficient strength in locations that called for Inconel eddie bolts,” AFM reports. Components are built with “twice the strength specified,” but he did not specify whether this was the case with the titanium eddie bolts, a Lockheed official told AFM.

But Lockheed Martin says the problem may not need to be fixed, according to AFM.

The JPO said “no aircraft operating restrictions or inspections are necessary at this time.”

JPO will release a fleet guidance report at the conclusion of the Root Cause and Corrective Action (RCCA) analysis now being performed by Lockheed.

“In addition to the F-35 production line at Ft. Worth, TX, the commingling of the two types of bolts was also discovered at the Italian F-35 Final Assembly and Check-Out (FACO) facility, but not the one in Japan,” writes John A. Tirpak of AFM.
As to how the issue occurred, a Lockheed spokeswoman told AFM that “several fastener bins were found on the factory floor with commingled fasteners at Lockheed Martin locations and several supplier locations.”

Similar quality issues occurred with the F-16, where workers threw leftover fasteners into the wrong bin at the end of a shift, AFM reports.

There are more than 48,000 fasteners of the two types on an F-35 fighter, according to AFM. The Air Force’s F-35As have 848 Inconel bolts out of 48,919 total fasteners, or about 1.7% of the total. The Marine Corps’ F-35B model has 877 Inconel fasteners out of 50,603, also 1.7%. The Navy’s F-35C carrier-capable model, though, which has to endure the shock of repeated hard landings on an aircraft carrier, and is larger and heavier than the other two variants, has 51,353 fasteners, of which 1,813, or 3.5%, are made of Inconel.

The JPO will work with Lockheed to “examine the structural impacts of having titanium fasteners installed in locations where the design calls for Inconel.”

The company and its suppliers “are validating correct fastener installations and have taken actions to improve fastener segregation and control,” the Lockheed spokeswoman asserted.

A Pentagon official familiar with aerospace structures told AFM it’s possible the titanium or Inconel bolts could be incompatible with the materials they’re attached to, causing a possible corrosion issue if left uncorrected.