787 LNAV

Quote from Beto McFly

I have extensive experience in reporting detailed bugs on mobile flight simulators and have helped developers correct these issues like X-Plane Mobile for example. But the preparation of these reports is quite laborious and I even spend about 1 hour and 30 minutes producing them outside the time I spend investigating the bug in the simulator and reproducing it accurately. I can commit to writing a highly detailed report but I need you to help me too because the more people report the same problem gets even better for it to be identified and corrected. For this specific bug it is necessary to record a video for developers to understand and identify the problem. The video needs to be recorded at the exact moment the bug occurs. At least here for me it has happened several times from the Boeing 787 LNAV and VNAV functions if they turn off on their own without my interference. When they turn off I turn them back to continue the flight.

I won’t be back in a 787 until probably next week, I did Newark to Madrid today on the 773 and will fly back to Madrid at the end of this week. My next flight will probably be Newark to lisbon so if this does happen again I’ll definitely try to record it. Saying that, LNAV hasn’t disconnected for me recently, I think it might just be the steep turns in the flight plan (although ThomK didn’t seem to have a problem). It’s hard to anticipate when the lnav will disconnect and what conditions have to be met but if it happens while I’m monitoring the climb out of Newark, or even when I get down route to lisbon I will definitely record the replay and show my complete lack of interaction which still causes a pretty crucial flight mode to just disconnect. Maybe my sim is cursed 👀

Update: maybe this is a thing. Concorde, IAD to LHR, and look at how many times the INS decided to disconnect and send me round in a circle:

Quote from Onizuka

I also encountered this problem on board the C172 when I activated the HDG on autopilot

hm. maybe the autoflight systems need touching up cos this happens in tht 787, concorde, and the 172 as well?

or just a fix to ensure the LNAV system doesn't keep routinely disengaging as my case with the 78-10 and concorde, it takes a turn and then ends up in a circle for some reason.

it tends to just disconnect and i think try to fly whateevr heading is set in the heading bug, although actually if it did this exactly surely it would straighten out once hitting the heading. It doesn't (the concorde doesnt at least, dont quite remember what the 787 did)

Edit: my current flight has just done it again, here’s exactly what it was trying to do

My guess is that it overshot the turn and this somehow caused INS to disconnect but when I found this it wasn’t changing heading, so probably a bank hold of some sort?

Quote from ThomK

I think

Guess that's what happens when the Speed is too high for the tight corner. 🤔

I mean I can’t really help doing Mach 2.04 ._.

Also the turn isn’t even that tight what are you on haha

Quote from Jet-Pack (IPACS)

It probably is that the turn anticipation of the route is broken again. The autopilot just flies what the route gives it and if that leg switching happens too late then the autopilot can't make the plane turn hard enough with the bank angle limit that it has.

Oh i see. is there a need for this to be fixed then or is this what should happen anyway?