ISSUE DESCRIPTION
TL;DR: 787 VNAV sometimes gets stuck on DES as soon is leaves the ground.
Some flights, seems depending on route, the 787 on take off (wheels off the ground) will immediatly switch VNAV to DES and pitch down to “land”. After that, no matter what you do, VNAV will remain at DES even if you land and try to reprogram/take off.
FREQUENCY OF ISSUE
Every other flight, but seems related to route
REPRODUCTION STEPS
This route always have this issue:
- Departure RJOO
- Arrival VTBS
- Set VFR (I never load IFR because its too buggy)
- Start Flight
- Set up CDU accordingly (RJOO → VTBS, in my attempts I used SID TIGER2, STAR NORT1C)
- Proceed to take off
- As soon the plane leaves the ground, instead of going into CLB, the VNAV switches to DES and commands a pitch down (if you follow the bird or turn the AP on it will just descent and crash)
- There is no way to reset the VNAV to CLB, so the flight is ruined OR you proceed without VNAV
YOUR SETTINGS
Happens on both Vanila 787 or Horizon 787-9 mod
Not that it matter but my specs: i5-14xx + 32Gb RAM + RTX4060 8Gb + NvE SSD
Hi @MSCaiobrz
Could you please upload some screenshots or a video showcasing this if possible?
Cheers
Will try to record on next flight.
I was not able to google a cause or solution, but surprisingly Gemini found an explanation:
"This is a well-documented behavior often encountered by users of the Boeing 787-10 in Microsoft Flight Simulator. It is primarily caused by a mismatch between the Flight Management System (FMS) altitude constraints and the aircraft’s current state during the transition from the takeoff phase to the climb phase.
The issue occurs because the VNAV logic interprets the next waypoint’s altitude constraint—or a default cruise altitude entry—as being below the aircraft’s current altitude or distance threshold. When the system incorrectly calculates the Top of Descent point, it switches into descent mode prematurely. Because the FMS logic is sequential and rigid regarding phase transitions, once it commits to the DES (Descent) phase, the logic path for the CLB (Climb) phase is effectively locked out.
This occurs both in the default Asobo 787 and the Horizon Simulations version, though the latter often exposes the flaw more frequently due to its enhanced system depth and more aggressive adherence to real-world FMS logic."
Can you load a link for the offending flight plan and I’ll try to reproduce? I have found the 787 hard to fly on A VNAV climb out unless all the altitudes are very carefully entered. One bogus number and all bets are off.
I gave a flight plan on my reproductio steps:
RJOO, sid TIGER2 → VTBS star NORT1C
Seems its more about SID issues rather than the destination, like you said unexpected altitudes cause the flight stages to bug out and go straight to DES
Hi, I have some time tonight and I programmed in an instrument flight plan:
Glancing at this it looks like it has the complete altitudes. You really need to do this as IFR to get all the details. If you are not instrument rated this can help you get started.
I will try to see if this runs in the 787-10. Generally I run on full autopilot. Normally I use FLC to get to cruise (20,000’) here and not VNAV. But will see what happens in VNAV. Normally you would also run LNAV.
[EDIT] The departure ran perfectly on VNAV with the target altitude set to 20,000. All the altitude restrictions are above something so it went right through.
I am not sure I have the time to run the whole flight but the approach into Bangkok is a standard ILS. On that once you reach cruise, set the altitude to 3,500 which is where you intercept the ILS and then set it off on VNAV again. It will descend at the TOD (Top of descent) point. To run the ILS you have to set APP for approach when you get within range. Probably under 6000’.
I suspect they have CAT III and it will do an autoland.
The 787 has a lateral/side view which you can get from the MENU top entry on the ND (navigational display). The 787 AP is next generation compared to the 767 and lower Boeing numbers.
Finally I have added the FLO menu to my system and they have a 4X speed-up option. I think this may be a keypress and maybe I can run the whole flight fast… 2000 miles to Bangkok!
I am on MS2020, I cannot use the flight planner
I had a similar issue therefore I stopped flying this aircraft. So frustrating. Sorry cannot help.
I think I cannot help you if you cannot use the planner or similar software to get all the fine altitude changes that occur in IFR/VNAV. This flies fine in MSFS2024. Maybe the time to upgrade to 2024 
Apparently you don’t user the CDU to configure your flights? You don’t need the planner.
Before takeoff its procedure to check if the path is right and look for discontiues, in this step if you don’t have the plan yet you can simlpy enter it on the CDU. I don’t enter full flight paths, usually just the SID and STAR.
In RJOO without any plan, if you set up your route (doesn’t matter destination) and enter the SID TIGER2 it will immediatly flash an amber light saying TD is sonner than TC (which is wrong). If you ignore it and continue your plan, this little surprise will happen when you take off.
To manually set up a plan, just use RTE to set up your current airport and destination (top left and right), EXEC to compute. Then you set up take off procedure on DEP ARR, choose DEP, then any runway, and SID TIGER2. When you EXEC the error will be set in motion
I will never use MS2024, I hate the always online aspect of it. As well the dirty move of Asobo by locking MS2020 users out of the flight planner to try and force you into it. Honestly I am waiting for X-P13
Ok I was able to take a few screenshots of my next flight and the issue appeared again, this time between VTBS → VABB. However, knowing that it is related to invalid altitudes on SID, I checked them up once the “UNABLE CRZ ALT - Computed top of descent is before top of climb confirm cruise altitude” error appeared, instead of clearing (because I assumed the SID was correct before) I started hunting them. Here is my quest:
- Screenshot 1: Route settings (the error pops up when you select SID, but I put this as screenshot 1 to show the route)
- Screenshot 2: Selecting SID, the errors pops up (sorry, I took a screenshot of the STAR)
- Screenshot 3: Looking at the SID’s legs, I can see it highlighted the offending leg: GUGOT has a 10000B altitude after I should have reached 10000 and on my way to 15049
- Screenshot 4: Page 2 of LEGS show another offending leg desput not highlight. NUNLI is the last SID and way into my cruise, but it set altitude as 16000 despite reaching cruize on the waypoint before (ANRIP, FL 350)
- Screenshot 5: Just to make sure, PERF INIT showing my cruise altitude is properly set
- Screenshot 6: After forcing a stepped climb on the SID waypoints (making sure each waypoint was at same altitude or higher), I was able to EXEC a new flight plan and the error did not pop up. New page 1 of the same SID, but with proper altitude in GUGOT
- Screenshot 7: Page 2 shows a proper NUNLI altitude. For some reason it was not letting me set altitude for this way point, I cleared the SID and restarted, fixed the altitudes BEFORE commiting to EXEC and the error did not pop up
- Screenshot 8: I was expecting it to work but took a screenshot of the takeoff setup anyway. The takeoff was successful and it went to CLB then CRZ properly.
So, in summary, Gemini’s description of the error is correct, the 787’s CDU is failing to interpret a non-ascending SID causing it to start descent as soon as it enters it.
>> The fix should NOT be going into DES, but ignoring the offending altitudes and continue the climb to the next valid entry. <<
Meanwhile, 787 pilots should ensure the SID have ascending altitudes as expected. I think the 2024 planner fixes this (thus it didn’t happen to A68yoSniper), and people who use Simbrief it will also obviously not feed erroneous altitudes.
I think we can consider this 2 bugs: Some SIDS have invalid altitudes being fed to the CDU (need to be tested in other aircraft to see if its the case and they ignore it, or the 787 is interpreting them wrong), and the 787 will get stuck on DES if this happens.
Interesting nuances to the AP. I fly with the Aussi Group and we had a very complex flight in Columbia landing at Bogata today. I ran it in a CJ4. Many steps up and down and one of the pilots noted some busting of altitudes on the VNAV on this aircraft.
Next time with them will ask about this. Some very experienced pilots there. They have a Business Jet and Airline flight each week. The airliner is at a bad time for me but I make the BIZJET. Guy who runs that is very experienced and likes to chat on Discord about procedures and knows his stuff better than I… that is what we use for radios.
I think most pilots will say make sure the plan is carefully continuous as this AP, though good, is a still a house of cards.
Ah… here is what we did:
The flight plans are published and you can run them yourself. About 6-8 pilots all levels experience.
Yeah it keeps happening and sometimes even fixing the plan doesn’t solve it (seems you need to fix, reset and refix to really guarantee the bug won’t happen)
Apparently I am the minority and setting up flight plans manually, but it is bugged and people like me without simbrief or 2024 flight plan are stuck with a buggy plane that can’t interpret strange SID altitudes.
I tried with a flight plan from the built-in MSFS 2020 flight planer and it didn’t happen because the flight planner leaves all altitudes empty. I usually don’t flt IFR because the ATC is buggy as hell, so it seems I have to go IFR, take off, ask to cancel IFR and proceed. 
I either work around the buggy 787 CDU with the above, or I will go back to payware 777
I also have the payware 777 and found it harder to program than the 787. They seem to want you to use Simbrief and to pay for it… if you want full IFR plans.
The 787 AP is next generation Boeing compared to the 777.
You might try the MS FlightPlanner which gives a visual representation of the flight plan with all the IRF options. It is the loaded directly into the AP from the EFB at startup.
If you do this by hand may find quite challenging. Is for me.
Below explains the 787 display work. This is on the MS version under the MENU for the big moving map.
The 787 Vertical Situation Display Human Factors Evaluation Enhan.pdf (584.7 KB)
Clear skys,
JY
I always program the CDUs from scratch on dark and cold, the 787 and 777 are extremely similar setting up the flight path, no issues whatsoever, and the payware 777 correctly ignores automatically filled improper altitudes.
I updated my answer without seeing yours while I was doing exactly what you mention, I used the build-in MS flight planner on IFR and there was no bug because it doesn’t fill altitudes, it seems to be the best workaround. since the game ATC is terrible I just canceled IFR after taking off and proceeded.
