Thread by @nileshjrane

So Lockheed Martin mixed up bolts and some of the critical areas on many of the F35 Airframes ended up with Ti bolts instead of Inconel bolts. Ti is significantly less strong than Inconel, and thus Inco bolts were recommended for critical areas.
airforcemag.com/lockheed-poten…

LM Spokesperson says it's very difficult to distinguish between the Ti and Inco bolts as they appear quite similar. Strike One - why there is no visible indicator on the bolts to differentiate if it could so easily lead to such serious lapse..?

The assy lines in Texas & Italy

had bolts found commingled. Stike Two - Non-robust processes and/or lackadaisical work culture by the workers on the Assy lines.

LM says no need to rectify the error as Ti bolts have sufficient strength even for critical areas. Strike Three - If Ti bolts had enough strength,

why Inco bolts were recommended by the designers in those locations at all..?? If the design was with Inco bolts there was certain safety margin inbuilt in the design. With Ti bolts, even if they are sufficient for the design loads, the safety margins would definitely be

significantly reduced. By how much and whether it still satisfies certification requirements, only LM structural engineers could tell. Bolted joints do have conservative design methodologies typically and are overdesigned. But it seems It seems counter-intuitive that Inco bolts

would be recommended even when Ti bolts are sufficient with Inco bolts costing 4x the money and significantly higher weight compared to the Ti bolts, especially when F35 has had pressure to reduce both weight and cost.

Funny, the inspection of some of the airframes "indicated high levels of compliant fastener installations”.

Earlier, a similar issue was faced with F16 as well, the article says. F16 is a contender for MMRCA 2.0 deal.