Chieftain Turbocharger run down times

[Centaurus]

The manufacturer recommends a "cool-down" time of three minutes at idle power after high power to aid cooling of the turbo-charger. Some operators set the throttles at 1000 rpm before engine shut-down, yet the manufacturer recommends idle rpm which is in the region of 650 rpm.

Surely if the point of the excercise is to cool down the turbines of the turbocharger until they stabilise at the lowest possible temperature, then seems to me that keeping the rpm at 1000 is defeating the purpose? Any comments?

Also some Chieftain operators maintain a minimum of 1200 rpm while taxying at night for battery charging with lights on etc and ride the brakes all the way out to the runway and all the way back to the tarmac to regulate the taxy speed at the higher rpm. Wouldn't this practice lead to hot brakes which might be needed in an abort? There is nothing in the manufacturer's POH about high rpm taxying to charge the battery so is it just another GA myth?

A Chieftain operator in Qld has brought in a requirement to check the magnetos at top of descent for dead cut at cruise power of 31MAP. While the mag switch is not switched off, the operator simply selects left then right magneto position to see if the engines runs OK. A dead mag will cause a big backfire and the theory is that delays on the ground can be anticipated and other arrangements made in plenty of time before the aircraft lands.

Again, there is no mention of this precautionary mag check in the manufacture's POH. I would have thought this was a potentially engine damaging procedure if done in flight if one magneto is proved to be dead and a large backfire is evident. Surely good airmanship would dictate that a check for dead cut is better left to after landing and back on the tarmac. Makes you wonder what CASA FOI's do for a living when this technique (airborne mag cut check) is apparently approved in the company Ops Manual.