The accident aircraft has a chequered history. Built as an EC-130Q for the US Navy’s TACAMO program, it served from 1981 to 1994 before being retired to the Davis-Monthan boneyard. Subsequently stored at Western International’s boneyard at Tucson, it was used as a spares source for the C-130 operated by the National Center for Atmospheric Research. It was then sold in 2017 to Coulson, who restored it to airworthy condition configured for fire suppression.
Good description of the aircraft and its equipment here:
Coulson and SkyTrac partner on Next Generation Air Tanker program