Lockheed-Martin, SpaceX, Ball Aerospace, whom I make parts for, 90% of the parts are specified for Heli-coils. Aluminum, steel, even titanium.

 

A thread insert done properly gives a repeatable known result and can even compensate for some inherent weakness in the metal, makes sense that they would be in use in planes, still doesn't mean they are the best solution to every situation, why the mass helicoil love and time-sert dislike? I'm 54 and have used helicoils all my adult life and only came across time-serts a few years back but I think they are a good thing done right.