VNAV Error + Autoland query

[SeaHawk14]

Good Afternoon,

On a flight from Marseille to Provence St Jacques I had an issue with the VNAV path. Everything up to TOC was fine, however when I was stepping through route I noticed that the TOD wasn't programmed until far too late, with an entirely unrealistic descent rate of something like 25000ft in the space of a few miles.

Consulting Navigraph it gave the waypoint of ENOKI at FL070 which I entered into FMC which caused the following crash in the gizmo plugin:

IXEG Error.txt

I'd pressed Clear and Reboot (then realising I'd have to re-configure the aircraft all over). The second time I experienced the exact same issue and the exact same crash. In the end with VNAV I just descended manually at an appropriate time. I think it's a very repeatable error, should you wish to try and replicate. LFRN Runway 28 ILS transition ENOKI (PDF's with waypoints there should you wish to duplicate). I know VNAV is a WIP however I've experienced this issue a few times now, where the FMC would keep me far too high, and when I've tried overriding it, GIZMO crash.

Additional Query:

I set the landing elevation on the Overhead as 130 feet, because the weather was OVC0300 I kept in Dual Channel autopilot for the full ISL autoland. The aircraft flared but it flared too early, about 10 feet above the runway, and then lost energy and touched down quite hard. I've used autoland very rarely, I've never had issues in the past however I'm wondering is it my fault for entering 130ft on the overhead (where as on Navigraph RW28 is at 121ft) or is this neglagible and the Autoland didn't function as well as it should have.

LFMLLFRN_PDF_17301092102.pdf LFMLLFRN_PDF_1730109210.pdf

[Litjan]

Hi Seahawk,

as stated here (check the last bullet point for FMS):

https://forums.x-pilot.com/forums/topic/8526-things-that-are-not-going-to-be-in-v15/

the VNAV calculations during the descent part of the flight may be erroneous, especially if restrictions are part of the path coding. Entering restrictions manually is further increasing the chances of things going wrong. For now we recommend calculating descent  paths manually, there is also a "descent path helper table" available in the documentation that you can refer to.

The landing elevation on the overhead panel is used to set up the pressurization system - it has nothing to do with autoland or the autopilot

Chances are that you used a wrong approach speed, the wind was unusual or your center of gravity was out of limits - however it is pretty normal for the 737 to not do a very smooth touchdown when using autoland.

Happy landings!

[SeaHawk14]

On 10/28/2024 at 1:48 PM, Litjan said:

Hi Seahawk,

as stated here (check the last bullet point for FMS):

https://forums.x-pilot.com/forums/topic/8526-things-that-are-not-going-to-be-in-v15/

the VNAV calculations during the descent part of the flight may be erroneous, especially if restrictions are part of the path coding. Entering restrictions manually is further increasing the chances of things going wrong. For now we recommend calculating descent  paths manually, there is also a "descent path helper table" available in the documentation that you can refer to.

The landing elevation on the overhead panel is used to set up the pressurization system - it has nothing to do with autoland or the autopilot

Chances are that you used a wrong approach speed, the wind was unusual or your center of gravity was out of limits - however it is pretty normal for the 737 to not do a very smooth touchdown when using autoland.

Happy landings!

Thank you, yes it wasn't a change of cruise altitude, but as indicated it seems to struggle with extracting restrictions/constraints. So just to make sure I understand, 1.5 has been released and is the X-Plane 12 version yes? Can we expect most of this to be addressed on 1.6, as I haven't seen anything about further updates ? I very much enjoy this aircraft and this is generally the only known issue with it.

[mjrhealth]

3 hours ago, SeaHawk14 said:

Thank you, yes it wasn't a change of cruise altitude, but as indicated it seems to struggle with extracting restrictions/constraints.

From what I understand is even in the real world pilots have to use speed breaks etc to reduce speed etc to make sure it all works,certainly in all my days of travel as passenger, it happened quiet a lot, speed brakes being applied on descent. Need to manage speed.

[Litjan]

15 hours ago, SeaHawk14 said:

So just to make sure I understand, 1.5 has been released and is the X-Plane 12 version yes? Can we expect most of this to be addressed on 1.6, as I haven't seen anything about further updates ?

Thanks for the kind words!

Yes, 1.5 is the current version for XP12. We are planning to updated the aircraft further in the future and are very aware of it´s current shortcomings, especially in the FMS department. Unfortunately we can not provide a realistic timeline as to when the next update will drop, we have a history of lengthy dormant phases and then stretches of working hard on the aircraft - both Tom and me do this as a side project in our lives in addition to our "real" jobs and family, so don´t expect the same cadence of updates that you would get from a dev team that does this "full time".

As you said, the plane can be flown safely, realistically and (I think) with having a lot of fun with it - I flew the real aircraft for 10 years and regularly fly our model in it´s 1.5 status and still enjoy that immensely...despite the shortcomings. I know this may sound apologetic, but real pilots (at least the older ones) still pride themselves in their ability to calculate and execute descent planning better than the FMS can .

Cheers, Jan

 

Edited November 1 by Litjan

[andrewjw19990]

@Litjan All the FMS does is make you Forget Math Skills LOL

Edited November 2 by andrewjw19990

[Litjan]

4 hours ago, andrewjw19990 said:

@Litjan All the FMS does is make you Forget Math Skills LOL

In a way that is very true! There was a famous accident with a Hapag-Lloyd Airbus A310 in 2000, they took off and wanted to fly to Hannover, but the landing gear did not retract. They looked at the FMS and it said that they could make it all the way easily...but the pilots did not know that the FMS did not calculate with the additional drag of the gear being down.
The pilots failed to do the basic "fuel flow x estimated flight time = fuel needed" calculation, instead relying on the FMS...and made a flame-out landing in Vienna because of fuel starvation.