Autothrottles for Light Jets.
 

Got asked in class today, why don't light jets that have FADEC such as newer CJ's Phenoms etc, why don't they have autothrottles.

I didn't have a reasonable answer so I thought I'd consult my panel of experts. I understand that on airframes where its a hydromechanical fuel controller set up its because of the weight and complexity. But in the newer FADEC controlled engines where the throttles are potentiometers, ie connected to wires and the computer schedules the fuel flow.

Would it make smaller jets more efficient...safer. Should all jets have autothrottles.

PC24 is to be FADEC.

Pilatus are also working on a FADEC upgrade for the PC12.

FADEC and Auto-Throttle are two different things- FADEC meaning the signals to the engine are transmitted digitally while Auto-throttle is part of the AFDS system, commanding levels of thrust depending on mode.

You can have either without the other, or both.

Are you sure about that? Even some light single piston aircraft have FADEC, eg, the DA40/42, Liberty XL ..

Which is exactly why he has typed "why don't light jets that HAVE FADEC..."

In light jets you normally set the power you want and the speed settles down to whatever it feels like.
In big jets the speed that is most efficient is far more critical so they need an autothrottle to hold that speed. (usually a mach number) Those speeds are determined primarily from weight and altitude.

The one word answer, I think, is 'cost'.