Welbaum said there are limitations to what a 747 can do. The plane must fly higher than other planes when it drops its load, for example, and no one is sure what that means for putting out or suppressing fires.

The 747 carried a fire extinguishing chemical with it to Chile in late January 2017.  No mixing base was required.  The water/chemical mix was used in direct attack and extinguished fires where it was dropped.  The chemical is a recipient of the Presidential Green Chemistry Challenge Award.  The chemicals in use cost is about 8% of the in use cost of retardant and 1/3rd the cost of the cheapest gel.  The chemical/water mix was credited with saving the town of Llico, Chile.

It’s not that the 747 can’t put out the fires, it’s a matter of if chemicals that can’t put out the fire no matter what aircraft they are used in are put in the 747.  Retardant is that chemical – it was not designed to extinguish fires.