The reason the Twin Towers fell on 9/11 was because the insullation covering the structural steel had been knocked/scraped off and the steel became brittle and crumbled from the raging fire. My architect brother told me this 20 years ago.
The insulation is a gunk like substance that gets sprayed directly on the steel. When it dries you can pull chunks off with your hand. A plane hitting a tall building will no doubt shake a lot of that stuff off and whatever is left won’t be enough fire protection. I was a NYC ironworker.
Yup. The impact and explosions would have stripped just about all the insulation off the steel. I think the architect stated he was amazed the buildings didn’t come down right away.