Cessna Longitude, autothrottle currently doesn't require power

Bug Reporting Hub Aircraft & Systems
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The autothrottle still adjust throttle to achieve target airspeed even when crucial aircraft systems that should be required for it to work properly are turned off. I am not a pilot and I am not familiar with the detailed technical implementation of the Citation Longitude’s autothrottle or any other aircraft but I’d assume that the calculation of the airspeed from the dynamic pressure measured by pitot tube should require power. Furthermore, the target airspeed is set on a digital adjustment wheel (AP settings).

Steps to reproduce

Get to a high altitude to be able to glide long enough to reproduce. Do all of that (in any order):
APU: OFF
Batteries (L+R+Standby): OFF
Engine L+R: STOP
Engine starters L+R: OFF
Fuel Valve: CLOSED
Generators (L+R+APU): OFF

Now all screens/instruments in the cockpit should be off. On the throttle there are two buttons to arm/disarm 1/2 auto-throttle. Press either of the buttons and auto-throttle is now armed or disarmed for both (the state changes even with power off). If you pull down the yoke with auto-throttle armed your airspeed get’s lower. Therefore if the plane was operating normally you’d expect the auto-throttle to increase the airspeed by increasing the throttle which is exactly what is happening. When you push down the yoke your speed get’s above the target airspeed and auto-throttle goes to idle as expected. However there is no way to power the movement of the throttle at this point. Especially not depending on the configured target-speed. It will not go to idle even in a sustained vertical dive when I have set the target airspeed to mach 0.8 for example.

Setup

I am on the Microsoft Store version.
No, I do not have any add-ons in your Community folder.
No, I am not using Developer Mode.

Build Version 1.19.8.0 was the first version I experienced the bug but I did not test a scenario that would reveal the bug in earlier versions. The recent Hotfix Version 1.19.9.0 did not fix the issue.

Medium graphics at 4K with 50% render scale and HDR.

PC specs

I am aware that the specs are low but the bug doesn’t seem to be performance related
CPU: i5-3470 (4x 3.2 GHz)
GPU: GTX 1650 (GDDR6, Driver version: 471.96, No updates available)
RAM: 12 GB (DDR3)
OS: Windows 10 Pro 21H1 (19043.1237, No updates available)

Zendesk ticket #124053

3

You never got a respinse? Dies it still happen? Were you just test piloting to see what it would do or did you have an emergency? Just curious. Ive never seen that done in a real 737 simulatorand if extra tine you can do a lot.

4

Yes, you are the first one to respond. Yes, the unexpected behavior is still present in version 1.26.5.0 of MSFS 2020. (NVIDIA driver 516.59, Windows 11 build 22000.778)

Simulating an emergency is probably the best way to describe how I discovered the issue. However, certainly more casual than a professional 737 simulator and probably not even close to how serious some people do emergency scenarios in MSFS 2020.

I want to clarify that I have not tested this scenario on a 737. I tried to do it on the B747 and B787 but neither are suitable for the maneuvers I described when completely turned off. The B787 is fly-by-wire therefore you are not more than a passenger without electronics. The auto throttle of the B747 just stopped responding even before I powered the plane down mid-flight.

In any modern airliner, including the 737, you won’t land or glide any longer distance without hydraulics. Without it good luck at moving the controls if they are even physically connected. And everything I know of that powers hydraulics will generate electricity.

I would assume that you could glide and land the relatively small Cessna Longitude without electronics. But the number of power sources makes it ridiculously unlikely to ever be necessary. It is effective at reducing the volume tough.

5

Maybe that little stb power equipment can do something in case of electric failure. Only answer to your thoughts what you can’t imagine. On other side i can imagine still existing bugs on stock planes.

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