Basic stuff the ground not being burned by the airplane crash that caused the trees above to burn.
It's a problem when the fire only burns feet above the ground. Which means there is nothing burning on the ground such as jet fuel, airplane parts, and the rest of the remains of a jetliner crashing.
A fire has a cause, if the cause is on the ground so should the fire and what it has consumed.
Why are the grass and ground cover not burned in these pictures?
Because there isn’t anything burning it up or it would be charred, smoldering, ash, or something other then grass and ground litter.

