IRON MAN ARRIVAL at LAX : unable to follow the VNAV profile

[Britjet]

Hi Hardy.
'hint" - sorry.
Don't get me wrong. PSX rocks..
I'll send you an email.
Peter.

[Hardy Heinlin]

Hi Peter,

that was technically meant. No problem at all.


Thanks :-)

|-|ardy

[Hardy Heinlin]

I just set multiple wind layers with opposite wind directions at wind speeds of 250 kt to illustrate the "snake effect" on the idle path. Of course, the vertical axis is very much zoomed in on this graph; the actual descent path is not that steep. But it shows the influence of the FMC FORECAST data. And these are the curves the deviation pointer on the ND will refer to. Only when the idle path is passed, the non-idle path begins and connects each waypoint by a direct staight line.



I set these excessive winds with the new Wind & OAT corridor tool where I can create up to 6 wind & OAT layers at each corridor waypoint. The radius of each corridor waypoint is 500 nm. The data is smoothly interpolated from the center out to 500 nm. -- When the corridor is embedded (by a checkbox) in the global weather model, the simulated MET office and dispatcher on the ground are able to uplink the respective weather data to the aircraft's FMC RTE DATA and FORECAST system.


|-|ardy

[DougSnow]

Every time I am in the JS and the crew grabs the speed brake handle to make the umpteenth profile fix or alttiude, this always goes thru my head...

https://youtu.be/5-knyUBbpgI?t=109

[Mariano]

Hardy,

This Wind & OAT corridor tool of which you speak, will it enable us to manually set wind and temperature parameters for enroute (cruise) waypoints as well?

Regards,

Mariano

[Hardy Heinlin]

Sure, for the entire route; that's its primary purpose. You don't even need to type it manually; just copy your external flight plan weather data text to PSX:
http://aerowinx.com/board/index.php?topic=4817.msg53551#msg53551


Regards,

|-|ardy

[Mariano]

Thanks, Hardy, that's great news.

Will we have the option of entering them manually? I am not good at any of these real world-to-PSX weather transposing.

Regards,

Mariano

[Hardy Heinlin]

Also manually, yes. (See that other thread.)

[Hardy Heinlin]

I'd like to explain one point regarding VNAV path deviation fluctuations:

First, it is important to understand that the turn radius at the active waypoint is a dynamic radius. The active radius varies with the current groundspeed until the aircraft enters the turn; thereafter the radius is frozen. This is a basic rule in the 744 FMC (real and PSX).

Secondly, the descent path construction prediction takes the distance-to-go (DTG) to the next constraint into account.

And the DTG varies with the turn radius:

The larger the turn radius, the shorter the DTG.
The larger the course change, the shorter the DTG.

A course change of 130° at a fly-by turn radius of 9 nm (fast aircraft) will shorten the DTG very much.
A course change of 130° at a fly-by turn radius of 3 nm (slow aircraft) will shorten the DTG just a little.
A course change of 004° at a fly-by turn radius of 9 nm (fast aircraft) will shorten the DTG just a little.
A course change of 000° of a fast aircraft will shorten the DTG not at all.
A course change of 000° of a slow aircraft will shorten the DTG not at all.

Now there may be an extreme aircraft groundspeed deceleration or acceleration whose start and end cannot be exactly predicted by the FMC -- e.g. when the pilots determine the flap extension start at their discrection -- and, say, a large reduction from 310 to 240 KIAS is to be performed. If such an extreme speed change happens shortly before a great turn or during a great turn, the FMC will have to change its predicted DTG accordingly. And this changed DTG will also change the aircraft's deviation from the predicted descent path:

If the aircraft has been on the path, and the DTG now unexpectedly shortens, the path moves laterally towards the aircraft's backside, and so the aircraft has to dive to get back to the path as the aircraft is now closer to the destination than predicted -- it's too high.

If the aircraft has been on the path, and the DTG now unexpectedly extends, the path moves laterally towards the aircraft's frontside, and so the aircraft has to add thrust to get back to the path as the aircraft is now farther from the destination than predicted -- it's too low.

Summary:

- Unexpected extreme deceleration/acceleration at a large turn will significantly change the DTG.
- The changed DTG will laterally shift the predicted decent path construction.
- The shifted descent path construction will cause the deviation pointer to move accordingly.

This is a logical effect I cannot eliminate. Please keep this in mind, skippers.


Regards,

|-|ardy

[Hardy Heinlin]

Does anybody know what kind of descent path the FMC predicts when a VECTORS leg is active?

Assuming the target waypoint has a hard altitude constraint and the VECTORS leg will not lead to that point:


(Aircraft at 6000 ft on VECTORS) --------------------------------------> 090°

(Target waypoint with 4000 ft constraint) <--------------- 270°


The aircraft's distance to the target waypoint is first decreasing, then it's abeam, then it's increasing.

As the distance is not continuously decreasing, the vertical path cannot be continuously descend either. When the distance is increasing and if the normal guidance would be applied, the aircraft would even have to start climbing.


Regards,

|-|ardy

[Hardy Heinlin]

Very drastic modifications regarding the entire VNAV descent system are now available in PSX 10.61:

http://aerowinx.com/board/index.php?topic=4191.0


|-|ardy

[double-alpha]

Hardy,
I do not know how much you've had to make the changes, but once again it's  a very good work.

I tried again the irmn approach (from my .SITU above), I let the plane fend for itself.
The VNAV mode is very soft and steady and works even better than the a340 real one (precisely on this approach IRMN).
The vertical path deviation indicator makes no longer yoyo and remains permanently visible (it disappeared from time to time with the previous version).
It's great, everything is perfect.

[double-alpha]

and by the way, thanks for the other part of the update 10.61

[Hardy Heinlin]

Thanks!

By the way, be sure that your FMC FORECAST data in your situ refers to the latest weather in case your situ file enables real-time weather downloads. If the loaded forecast data is correct, the path prediction will be even better.


Regards,

|-|ardy

[cagarini]

Same here :-)

Flew it all the way down to touch down, beautifully!

And in my case, and since the default situ does not enable RWW and I was using it, and didn't update the FMC forecast, it still did it perfectly!

Thanks!

[Hardy Heinlin]

Further improvements in the VNAV DES system are now available in PSX 10.63:

http://aerowinx.com/board/index.php?topic=4191.0


Regards,

|-|ardy

[ScudRunner]

Incredible commitment - thank you very much Hardy!