747-8I has problem with LNAV and HDG on Autopilot

[bebongnuoc]

Yesterday I made a flight between EDDH and KJFK with the 747-8I. This aircraft only followed the route for an hour. After this time, she became uncontrolled by Autopilot anymore even I had tried engage and disengage the autopilot, activate again the route but none of them worked. Can anyone know how to fix these issues? Thank you!
Here the link to the model: https://github.com/FGMEMBERS/747-8i.

[Octal450]

@bebongnouc
Can you give a more specific details???
Which exact buttons did you do, and which route, maybe I can reproduce?

AP always worked fine for me.

[bebongnuoc]

I made the flight between KJFK and EDDH, FL390, 0.86 Mach. I use LNAV + THR + SPD + FLCH then V/S + CMD to reach FL390. But after an hour in flight, LNAV didn't work anymore. I switched to HDG but even I turned the knob, it wasn't working at all, the 747-8I didn't turn.
.
I had set to fly over England before the flight go on sky. How ever when I check it again, I decided to turn off the autopilot then make a turn to land at LPLA.
http://mpserver15.flightgear.org/modules/fgtracker/?FUNCT=FLIGHT&FLIGHTID=6699695
Here is the route to load in flightplan:
https://drive.google.com/file/d/0B8mXuLph1YAsX2RHcGxEMHV4YWM/view?usp=sharing

[Octal450]

Hmm OK.

I'll check it out.

[tikibar]

Short answer: you're flying too fast.

The typical cruise speed for the 747-8i is 0.855 mach. If you have the bank angle limiter set to AUTO, it will not allow the AP to bank if your speed is M0.86 or higher. If you can't bank, you can't turn, and you can't follow the route. If you must fly that fast, adjust the bank limiter knob to something other than auto. Otherwise, slow down, then it will work fine.

[bebongnuoc]

Short answer: you're flying too fast.

The typical cruise speed for the 747-8i is 0.855 mach. If you have the bank angle limiter set to AUTO, it will not allow the AP to bank if your speed is M0.86 or higher. If you can't bank, you can't turn, and you can't follow the route. If you must fly that fast, adjust the bank limiter knob to something other than auto. Otherwise, slow down, then it will work fine.

I know. I tried to reduce the speed to 0.84 Mach, I even decent to FL300 with 0.82M but I can't use either of them. The most important issue is after reaching FL390, it could controll the aircraft about an hour then it didn't.

[Octal450]

I really don't know what you are doing, I cannot reproduce the problem.

Even forcing it up to Mach 0.9, still followed my LNAV without any problem.

[tikibar]

I've got many flights in this aircraft, some over 15 hours, some up to FL410, and have not had this problem with LNAV as long as I've not flown too fast.

Without an error message from the console, it will be impossible to diagnose your problem, since I can't reproduce it.

If you do run into problems with the AP, there is a reset feature you can try. Go to the 747-8i->Control Panel, then click "Advanced..", then click "Reset AFDS."

[bebongnuoc]

I will try again. Thanks you guys!

[SP77]

i have been having the same issue, im flying at .5 mach, put in a course like from Boston to JFK. every time i hit the AP button, it just pops out so it wont engage. from the console i will hit the A/P CMD button and it turns yellow for less than a second so it wont set. my bank limit is auto, i even went to the control panel and reset the AFDS but AP will not engage. it used to work for me fine for 3 weeks but this last week i cant get the auto pilot to set

[SP77]

i also noticed another issue, when i set my IAS for 250 speed, then i hit the AT armed box then hit A/T. i could be flying at 260 knots but my speed indicator for knots will jump up to full throttle, while that is still set at full throttle, i will lower my speed down to 200 but the indicator shows me at full throttle and gaining speed. yet at the same time still no A/P will engage at any speed

[tikibar]

It sounds like the AP disconnect switch may be tripped on the panel. It would help to know what version of FG you're using, where you got the aircraft, and what error messages you see in the console.

[SP77]

same issue here also. i can set the speed at 200 or even 250 knots, ive even taken it down to 100 but the speed indicator goes to full throttle as soon as i hit the A/T button. when i go to control panel then advanced then hit reset AFDS, i can get my AP to work for 2 seconds. as soon as the AFDS switch pops out my auto pilot goes off again. i am using flight gear 2016.2.1. i even took out the plane from my computer then re loaded it with the USB stick i bought but same problem as before. it was working for me 3 weeks then the last 2 weeks i cant get it to work. i do not see any error messages on the console.
thanks

[tikibar]

When you're having this problem, could you open up the AP dialog (hit F11) and take a screenshot and post it here?

Also, where did you get the aircraft?

[SP77]

all planes were purchased with a USB stick from FG
here is link of screen shot https://www.dropbox.com/s/g8zlm3bg46t1x ... .docx?dl=0
also noticing problems with speed with auto pilot on other planes. an example is the 777-300ER, a great plane to fly yet under auto pilot which works, if i have the setting V/S on and going up 1000' per minute, the speed or A/T will not engage saying auto throttle cant be engaged while under 500' (maybe 200') yet im at 10000'. as soon as i disengage V/S and engage ALT instead, i can get my speed settings yet only at full throttle. very confusing as everything worked fine but now everything related to AP is crashing