Nacelle Anti-Ice and Engine Idle

[John H Watson]

There has been some discussion behind the scenes regarding whether or not all engines should increase their idle speed if only one engine's Nacelle Anti-Ice is turned on.

I can find no airplane logic to say that the engines which don't have NAI selected ON should increase their rpms (either in training notes or in wiring schematics).

If individual engines can go into high idle, you would think that you would get an IDLE DISAGREE message, but my books show logic inhibiting this message if NAI is selected on in flight.

Automatic NAI activation, of course, should put all engines in high idle, because the ice detectors are located on the nose (remote from the engine nacelles). The detectors don't know which nacelles might be icing up.

Thoughts?

Rgds
JHW