It's concerning because the 15% is primarily driven by an unexpected flaw in the engine. As estimated in the article, the hoped for engine-less rate (driven pu

It's concerning because the 15% is primarily driven by an unexpected flaw in the engine. As estimated in the article, the hoped for engine-less rate (driven purely by maintenance cycles) would be ~5%. Also as noted in linked to articles, the mission capable rates (MCR) had increased from 62 percent in FY2019 to 76% in FY20202, and that was a big deal. At 76%, the F-35 had the highest MCR in the USAF fleet (the legacy airfames were all sitting around 70%). With the engine problems, we can estimate that it's could be knocked back down to ~60-65% (though obviously there are probably ways to shuffle engines around to reduce the impact somewhat), bringing it back to the bottom of the pack (well, F-22 is below it at like 50%... but whatever).