[Fixed in next patch] FMC crash caused by VNAV calc with routes consisting of 1 waypoint

[fortin]

Steps (most of those are probably irrelevant):

- Start at gate B19 at CYYZ

- Cold and dark state

- Start Battery

- Connect Ground power and activate. Set IRS knobs to NAV

- Enter Weight & Balance in the Xplane 12 menu (9000kg payload, 5800kg fuel), apply changes

- Enter 47.0/23.9 in weight/cg

- Enter 1 in fuel reserve

- Enter 17 in Cost Index

- Go to POS init page, Next page, Grab Left GPS coords, paste them in the align slot

- Go to Route

- Enter from CYYZ, to CYUL, Next page

- Enter MIGLO as the only waypoint

- Activate

- Exec

At that exact moment, see screenshot. The aircraft essentially crashes. The FMC starts displaying on the PFD, and becomes unusable without a restart.

This has happened to me on 4-5 different occasions, though it doesn't always happen on this route. So I'm not 100% clear on what triggers it. But it seems to happen 50% of the time.

 

Edited September 20, 2023 by fortin
added a closeup screenshot

[fortin]

I should add that I'm using the 2309 rev 1 Navigraph AIRAC cycle, if that affects anything. Though by that point I hadn't reached the point of picking a SID or STAR, was just plugging the single waypoint of the route (MIGLO).

[tkyler]

A few missing points.  That error is part of a VNAV calculation, which would only run if you had set a crusie altitude, which you didn't mention in your steps so I couldn't reproduce.  For VNAV calc to run, you need your PERF info on the PERF INIT page, and then a cruise altitude and of course a route...(without a disco in the first line).  When you execute with those "minimum requirements", then the VNAV calcs will run.   Most of the other stuff doesn't matter.  I'll try to reproduce give the general Departure airport and one waypoint...with the perf init/cruise alt, that should be enough for me to test.

-tk

[tkyler]

...was able to reproduce.  bug logged.  Thx.

-tk

[tkyler]

fixed.   I had a '>'  instead of a ">="

DOH...tk

 

 

Edited September 20, 2023 by tkyler

[tkyler]

@fortinworkaround....put two waypoints in the LEGS page at minimum before executing.....that should get you past the error.....then after you get airborne,  you can put MIGLO into the first line and execute if that was your intended plan (one waypoint only).

Looked like the crash happens when running a VNAV calc with only one waypoint in the legs page.  Already fixed for next patch.

TK

Edited September 20, 2023 by tkyler

[fortin]

@tkyler Wow! Thanks so much for looking into this. You're absolutely right I forgot to mention that the Crz Alt was set in the Perf page.

I work in tech and I know the pain of dealing with a bad bug report. Shame shame shame ding ding.

Glad you found the fix and that it was ultimately simple. Looking forward to the next update and thanks for the workaround!