VNAV on 747 (and 737)


I’m on on Xbox

I have tried flying the standard 747 and the Bredok 737.
I have issue with the autopilot and VNAV.

With AP and VNAV engaged, the airplane does not keep the selected altitude.
Also the AP panel shows 10000 selected altitude, while the HUD in the external view is showing the cruise altitude.

Steps to reproduce

  • take off in the 747 (or 737)
  • select an altitude on the AP panel (different from the cruise altitide)
  • engage AP and VNAV
  • the airplane does not keep the selected altitude
  • the HUD on the external view shows a different altitude than the one selected

Forgive if this offends, but have you set your altimiter to the current pressure reading or, if 18000’ or higher, to STD (29.92)?

If you are doing that, have you engaged the Auto Pilot to ascend/descend to the altitude set in the altitude hold window?

Yes I did.

So help me understand the issue better. I’ve done a significant amount of testing with the 747 recently and I’ve not run into this issue, that I’m aware of. I say “that I’m aware of”, because I do not fly the aircraft externally, and if I happen to switch the external view. I have the HUD turned off, so I never see what the gauges there are reading.

Ok, that out of the way.

Let’s say, prior to take off in the 747, I dial 8000’ into the autopilot and turn on LNAV and VNAV. When I take off and engage the autopilot, it climbs to 8000’ and holds that altitude.

You’re saying that you’re not seeing a behavior like this, but instead it holds at some other altitude? How far off from the setting is it?

I have started using it, now that it has some real liveries.
I have also tried the same on the 737. I think it shares the same avionics of the 787.

I’ll try the 787 and the a320 and report.

I’m testing this right now and I don’t see what you’re seeing.

I’ve got 8000’ on the AP and I’ve got 8000’ on the altimeter and I’ve got 8000’ on the external HUD.

What do you get when you do this? You didn’t say how much of an altitude difference you’re seeing.

I just noted you tagged this Xbox, so I am running the same test on my Xbox right now and there is no change from the SU8 beta PC version.

The Xbox is reading 8000’ on AP, 8000’ on altimeter and 8000’ on external HUD.

that’s because the broken 737 does share the avioics of the 787. it’s not a very well made plane i think it’s an airbus with a 737 skin on it with 787 cockpit.

You may need to push the alt knob on the MCP in order for it to register the new altitude (left click)

Ok, I sorted that out: I had to click on the knob to confirm the altitude.

Thanks for your help

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All - VNAV and LNAV are tied in some way to the FMS computer. They do not work, if the FMS has not got the requisite information those conditions need.

It has taken me months to get this information, and I got it from an X-Plane 11 video. So, it will help you if you understand and can program the FMS.

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