AP unable to follow RANS1B SID out of HAAB

[alstr]

I was flying the RANS1B SID out of Addis Ababa/HAAB and after engaging the AP as usual shortly after takeoff I noticed the aircraft started deviating from the route.

Here is the SID in pink and the route the aircraft took:

 

The route was correctly loaded into the FMS and looked right on the display.

It is quite a technical departure with numerous turns in quick succession and overlapping paths, so is this just a limitation of the flight computer? One to fly manually?

[skiselkov]

Cannot reproduce:

[Pils]

12 hours ago, alstr said:

I was flying the RANS1B SID out of Addis Ababa/HAAB and after engaging the AP as usual shortly after takeoff I noticed the aircraft started deviating from the route.

Here is the SID in pink and the route the aircraft took:

The route was correctly loaded into the FMS and looked right on the display.

It is quite a technical departure with numerous turns in quick succession and overlapping paths, so is this just a limitation of the flight computer? One to fly manually?

I think it starts to go “wrong” (it flew what the coding was in the database but not what was depicted/expected) when it turns inside the Navigraph estimate and reaching the 10500’ restriction too soon. Were you flying at 185 kts max as charted the whole time?

[birdy.dma]

A little pic of the chart

 

 

[alstr]

15 hours ago, Pils said:

I think it starts to go “wrong” (it flew what the coding was in the database but not what was depicted/expected) when it turns inside the Navigraph estimate and reaching the 10500’ restriction too soon. Were you flying at 185 kts max as charted the whole time?

Yes, I had 185kt dialled in as the max speed and didn't exceed that.

On 7/6/2026 at 6:33 PM, skiselkov said:

Cannot reproduce:

I can't explain why my flight differed then. I've not tried it again since but if I get chance I will.

[alstr]

I have tried this SID 3 different times and got a different outcome every time. Here's how it was programmed in:

I've included videos below of each attempt, the most pertinent probably being number 3, which reproduced what I described in the original post. (Edit: these videos seem to stream horribly, I'll try reuploading them shortly).

Attempt 1:

Aircraft generally seemed to follow the correct route as drawn on the chart, but climbed incredibly slowly for some reason, resulting in terrain and gear warnings, so I decided to restart. Closest to the one shown by @skiselkov.

Attempt 2:

Aircraft loosely followed the correct route, making the correct turns at the correct altitudes, but took some quite sharply, so deviated from the mapped route. Maybe that's okay, I'm not sure.

Attempt 3:

Here the aircraft turned in the opposite direction to that on the chart and the FMS, as I described in my original post.

I didn't vary anything between the 3 attempts, other than tiny differences in my inputs and timings. Please excuse poor FPS and strict adherence to checklist while I was juggling a few things.

Maybe I did something wrong, if so please let me know.

Edited July 8 by alstr

[skiselkov]

Please also attach a Log.txt from the sim when running this departure in the aircraft.

[alstr]

I've attached a video and the log file.

 

Log.txt

[Pils]

3 hours ago, alstr said:

Maybe I did something wrong, if so please let me know.

You're flying the climbs in PTCH mode (and at a pitch less than 10 degrees in some cases), while not accelerating past 185 kts (as per the chart). From what I can tell the plane flew exactly as you commanded it to, at low pitch and low thrust (due to low speed target), with attempt one being the lowest (zero climb rate/VS at times, should be something you're monitoring). After initial take off phase you should be switching vertical mode to VS or FLC. The plane is capable of climbing at several thousand FPM, not hundreds. Obviously in hot weather (like ISA+19 you have) and with a heavy fuel load that will be lower.

4 hours ago, alstr said:

turned in the opposite direction to that on the chart

FWIW the chart may show this, as that's what's expected, but it's not enforced in the database coding. If you leave the PFD ROSE in HSI mode and the CDU on the LEGS page you'd have shown what exactly it was flying more clearly. The popup makes it easier to see the DTK, it was flying to course 331, which is a "shorter" turn by going to the left.

I think it all comes down your procedures, and the plane is flying exactly what the database tells it to.

Hope this helps.

P.S. X-Plane's default video capture is terrible, I suggest using OBS Studio. Also uploading to YouTube or Streamable.

[Pils]

4 hours ago, alstr said:

so deviated from the mapped route

The route on the plane's map isn't like an Airbus where it'll fly exactly along the line, so some deviations are expected.

Looking at attempt 3 again (at 4x speed???), I see it did draw a turn to the right, but when it sequenced it took the shorter path to the left. That's maybe a corner case that the developer needs to address.

But, I think to get you passed this issue, an adjustment to flying technique will put it inline with what's expected (and demonstrated by us).

Edited July 8 by Pils

[alstr]

Yes I'm sure it's partly down to technique. Usually I use VS and FLC to manage the climb after takeoff but usually it still climbs quicker than it did in the first case. I just found it a bit odd, and it didn't happen any other time.

I sped up the video 16x because no one wants to watch three videos that are nearly 10 minutes each, and I thought it gave the basic idea. But yes they could be better and it took me forever to upload it so next time I'll do something else.

Attempt three, that is really the confusing one as like you say, it turned left despite definitely drawing a turn to the right, and the departure instructions explicitly say right turn:

Quote

Turn as soon as practicable, intercept ADS R077 to at or above 10500, turn RIGHT to D6.0 ADS, turn RIGHT to ADS, ADS R317 to D23.0 ADS, then follow respective procedure.

I don't know what the database explicitly says in this regard, but I would have expected it to enforce the above in the main. I think a left turn would be a significant deviation as flying over Addis Ababa city below FL160 is not permitted and the pattern is tightly regulated. But I'm just some dude flying a flight sim and neither a real-world ATC or pilot.

Edited July 9 by alstr