why does the auto throttle get stuck at 392?

Question

Hi,

the flight plan for this flight was to be flying in a Boeing 737-800 at 30,000 ft and are speed was planned for 450 knots.  So I was turning the auto throttle nob for the auto pilot and then it got stuck at 392.  In other words it would not turn when it got to 392 it would go to 391 and 390 and so on but not 393 or 450.  Does X-plane 11 only simulate up to 392 knots?  Or is there a way to make it go higher.

Answer 1

That restriction may just be the maximum airspeed that the aircraft would allow into its auto-throttle setting.  The value in the panel is in Indicated Airspeed (IAS).  At FL300 (or higher), for IAS of 393, I can imagine the equivalent True Airspeed (TAS) would way exceed the limit for the B737-800.

For example, if you want to cruise at 450 kt, at FL300, the IAS may be around 285 kt—depending on atmospheric conditions.

Comments

Sorry but I don't really understand what is going on here because I was just in a boeing 737-800 and I got the airline app and it told me we were up at altitude and we were going 450 knots.

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The explanation can be found here: https://www.boldmethod.com/blog/lists/2019/11/the-four-types-of-airspeed-and-how-each-works/

The speed that your airline app was showing is in True Airspeed, which is how fast your plane is really--truly--slicing through the air.  In short, what is indicated in the 737’s Primary Flight Display is Indicated Airspeed (as the name implies); which is also what you would enter into the autopilot.

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Okay I get it now but there is one more question.  In real life it take about 55 minuets to fly from KLAX (los angels) to KSFO (San Francisco) but it took me 2 to 3 hours!  My IAS said 300 knots.  Is this a bug?

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What framerate are you running at?  Your sim could be suffering from this “Slow motion” syndrome…

   https://www.x-plane.com/kb/the-simulators-measurement-of-time-is-slow/

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Thanks dick I found the frame rate that my simulator can run at and so far so good.

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So if you fly the 737-800 what is your IAS in the auto throttle?

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This post is getting too lengthy and off topic.  I’ll MP you to follow up…