Actually as ARFF, we are trained to attempt aircraft shutdown. We use the acronym TBABB
Throttles - Idle
Bottles - Activate the shutdown and fire bottles
APU - Same
Battery - Master Switch off
Battery - Disconnect externally
Foam doesn't change the story, and yes the amount out of a fire hose or even the turret of the truck may not be enough. First you have to realize how much bypasses the actual engine core. Once the water gets dispersed by the fan blade, the compressor blades, and all the stators and other obstructions, very little gets to the burner section. As ARFF, we are trained that we can try it as a last resort, but don't expect it to work.
*Note, I am a 12 year ARFF veteran