I'm sure this has been brought up before, but does the Banner of Eternal Flame confer flaming attacks onto characters in the unit with magic weapons? I've heard claim that the magic weapon is unaffected, but I can't find text to substantiate this.
I see no reason why not, the banner makes no exceptions for magic weapons. I assume it would be the same for armor piercing banners.
The very last sentence of the flaming attacks rules in the brb, page 69, the part in ( ). clearly states that magic weapons do not benefit from flaming attacks. So no, unless the weapon itself has flaming attacks, there is no way to give a magic weapon the flaming attacks property.