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When i press IAS button on the awesome Citation X i downloaded here, the button doesn't light up and i can't use the wheel to set speed. also i can't control the VS with the wheel either. to my understanding in citation you can use the nose up/nose down wheel right next to the AP/ALT/IAS/FLC etc. buttons to set IAS and VS if you press the correct buttons but IAS button doesn't work.
also there is autospoiler button that seems to work, at least it says on the screen that autospoiler armed but the button doesn't light up. and there is autobrake buttons but they don't light up either, i don't know if they work at all.
I know you can popup autopilot control panel and use that but it would be cool if the 3D cockpit buttons would work also.
Other than that the Citation X is really cool and quality addon, one of the best freeware models there is.
Interesting question. I haven't tried the Citation X here but being familiar with the real life Citations, I know that none of them have auto throttle, auto spoilers nor auto brakes. Perhaps that's why the buttons don't work on this simulator. It could be possible to find a modified CitX in real life with those goodies but I don't think they are factory installed afaik.
If this keeps you from enjoying the airplane, you could copy the needed gauges from another airplane panel and customize the existing one. But that's a lot of work.