should the pilot launch into a typical engine failure drill appropriate to a piston twin (say PA31 or C404)...the proceedure, power lever idle to confirm the failed (piston) engine, will disable the King Air auto FX with predictable results.
I have often wondered about the commonly taught practice at some flying schools of "power lever idle to confirm the failed engine."
This practice is not mentioned in any of the aircraft manufacturer's flight manuals I have read over the years with the exception (if I recall correctly) of the Beech Baron series. The primary identification method is normally by rudder use as in 'dead engine dead leg."
The problem with pulling back the throttle of the assumed dead engine, is how fast does the pilot pull it back? Slowly or quickly? All the way back or just enough to see if any change in foot load or direction of yaw?
All this takes several seconds with the dead engine propeller still windmilling with associated high drag and loss of airspeed. Keep in mind some propellers on piston engine aircraft will not feather if the windmilling RPM gets below a specified figure - typically 800 rpm.
Having said that, with the four engined aircraft of yesteryear, there was a case for confirming a dead engine by pulling back its throttle. A strong yaw could indicate either a port outer or a port inner engine problem. Dead side dead leg was primary identification on which
side. But which of the two engines on that side? Selective throttle closure combined with engine instruments narrowed down the culprit and then appropriate feathering action made.
With an engine failure at a critical moment after lift off in a light twin, the priority would be to quickly reduce drag. That means feather asap. For every second the prop is allowed to windmill, its drag will cause aircraft speed to will degrade alarmingly. In some aircraft there is more drag from a windmilling prop than from an extended landing gear. Often the pilot cannot afford the luxury of a careful pull back of the throttle to confirm the already identified engine.