Wait, flaking inside the flue isn't a good thing?

Buddy of mine saw that exact thing in a Cessna over Tucson.

Man, 3,000 degrees? I'd be sweating through my jeans just standing next to my forge at half that, lol. My little propane setup's lucky to hit 2,200 on a good day, and even that feels like standing on the sun. @palmer.avery's right to question it, though I bet those old coal guys were just running their mouths or measuring something in a closed firebox. I once melted a pair of tongs just trying to hit welding heat, so I can't even imagine what 3,000 would do to my shop.