Why do so few regional and bizjets have autothrottles?

[Daniel Churchman 1050104]

It seems such an obvious thing to have, and so easy to implement. Many of these jets have speed control while climbing, which of course is not via altering the power setting, but rather by altering the rate of climb.

 

Many of these have FADEC, which surely shouldn't preclude a simple speed control.

 

And specifically, within FSX, I find setting the throttles to CRUISE does not prevent over-speed, which is my primary concern.

 

So why is it this is missing? Some bizjets have pretty long ranges, so many hours will be spent at cruise. Surely real world pilots have to contend with this too.

Edited August 25, 2017 at 11:13 PM by Guest

[David Zhong]

"Cruise" power is not necessarily a setting that is suitable for cruising... for example, on Boeing jets, this will give you maximum cruise power, which will quickly take you to overspeed!

 

"Easy" is very subjective... even a basic PID controller requires testing and tuning to produce a system that behaves properly, which has a cost [Mod - Happy Thoughts]ociated with it. Even worse, in aviation, every extra bit of gear you put in the plane requires another aviation regulator approval (which again has a price tag [Mod - Happy Thoughts]ociated with it). So at the end of the day, it depends whether the manufacturer believes that their customers want the feature.

[Daniel Churchman 1050104]

....

Thanks David.

[Andreas Fuchs]

And don't forget the weight of such a system and the space that it takes. In some aircraft it is simply not available. I used to fly the Embraer RJ145, no auto-throttle. Then the Citation 560XL Excel, no auto-throttle. Now, on the Falcon 2000EX EASy we luckily do have it, but its predecessor, the Falcon 2000 "Cl[Mod - Happy Thoughts]ic" did not have any automation for thrust. Still, you do not go into overspeed that easily. Just keep some margin between your target speed and the maximum allowable speed. Usually we did set thrust in a way that the plane's speed would float around the target speed by about 5 kts. If you now leave 8 or 10 knots margin to the red line, you should be covered, except for encountering turbulence, mountain waves etc..

[Er-Jin Jang]

As far as I know, the reason why so few of the smaller airplanes have autothrottle is not only because of the weight/space involved with such equipment, but also the certification hurdles they manufacturer would have to overcome. Interestingly, AT is a *relatively* new system, compared to APs which have existed for more than half a century by now.

 

The good news is, however, that with recent advancements in tech, we're starting to see AT retrofits in smaller/less expensive aircraft as well. In June, the FAA issued an STC to IS&S for an AT to be installed in PC-12s. IS&S is working on more STCs so the ATs can be installed on other PT-6 powered airplanes.

[Christopher Liu]

The provision of autothrottle has traditionally been [Mod - Happy Thoughts]ociated with autoland and sophisticated climb VNAV that uses cost index and is coupled to the autopilot. These systems generally weren't found outside of full-size airliners (737, A320 and bigger) so neither was autothrust. I can't say I missed it all that much, you just have to remember to adjust the throttles whenever the aircraft levels off, but you should be paying attention anyway! FADEC is just there to set an upper limit of what the engines can safely output.