Winds Aloft & Inputting them to the FMC

[fro2do 10]

When I complete my flight plan with PFPX and I get the latest winds and temps for the day...when I export 

them to the fmc and I start comparing them during the flight there is a discrepancy to them all.

 

I know that the weather is dynamic and it is trying to compute but how far off is it?

Is there a fault tolerant, and how much?

 

Once I request the winds to the fmc how come I can't change it to the true values at a certain Vor or waypoint during flight?... and because of the wrong data will it interfere with the entire flight plan.

 

Thanks.

[pcubine 143]

When I complete my flight plan with PFPX and I get the latest winds and temps for the day...when I export

 

them to the fmc and I start comparing them during the flight there is a discrepancy to them all.

 

Giancarlo

Are you using Online (PFPX), AS2012, or REX as your source of winds aloft?

 

Edit

This is part of a post I made in the PFPX forum. “:I am using AS2012 for the weather and that is selected in PFPX  options. I start AS2012 first and let it run until synthesis completed appears on the status page. I then enter the flight plan which will later be entered into PFPX  as a copy/paste over the PFPX generated plan. I print a NAV LOG and Coded Route Route Weather from  AS2012. I then complete PFPX , release the flight and print the OPF. When comparing the winds at FL340 from AS2012 to the winds from PFPX at waypoints there is a difference. Between running AS2012 and computing the flight in PFPX there is no more than ten minutes elapsed. This has happened on numerous occasions . So I believe the time deference  does not account for discrepancy.”: I assume both PFPX and AS2012 use NOAA as their source of information so you would think the forecasted winds would be the same at each waypoint. However the direction and speed may disagree by 5-10 degrees and 5-10 knots. The whole deal is a mess before you even import the winds into the FMC. But you must remember these values are only forecasts and the winds you encounter during the flight are real and could and probably will be different. What is acceptable? I would say anything as long as ii is not off by 180 degrees or 50 knots at a waypoint proceeding a long leg. I have no idea where the allegedly real weather comes from. Maybe it comes down from Mount Sinai in tablet form delivered by Moses like the Ten Commandments were. Who knows?

 

Michael Cubine

[scandinavian13 5,192]

 

 

when I export 
them to the fmc and I start comparing them during the flight there is a discrepancy to them all.

 

Have a look here:

http://forum.avsim.net/topic/418750-pmdg-777-issue-tracking-thread-read-before-posting/

 

Specifically:

 

Found / Fixed / Added for Future Update:

[...]

- Wind import .wx file is no longer locked from being written to after initial WIND REQUEST and can now be updated in flight.

- Fixed ACT WIND page ordering. (pages 1 and 2 missing etc)

[fro2do 10]

Thanks Michael Kyle for you help I love the bit with the ten commandments but Kyle I read 

that statement but I'm confused I am using Active Sky for the winds but once I export them

to the fmc I can't change it... so is it not working yet or am I doing something wrong?

 

Sorry about this guys but still a bit confused.

altb

Giancarlo.

[scandinavian13 5,192]

 

 

but Kyle I read 
that statement but I'm confused I am using Active Sky for the winds but once I export them
to the fmc I can't change it... so is it not working yet or am I doing something wrong?

 

As I quoted from the issue tracking thread:

The feature is not working as it should.

You cannot update the winds once you've requested them.

 

Both of these issues will be fixed after the next update.

[fro2do 10]

 

 

As I quoted from the issue tracking thread:
The feature is not working as it should.
You cannot update the winds once you've requested them.
 
Both of these issues will be fixed after the next update.

Ok Kyle thanks I understand now.

[Flamin_Squirrel 71]

how come I can't change it to the true values at a certain Vor or waypoint during flight?.

 

You wouldn't change them in flight anyway.

[fro2do 10]

 

 

You wouldn't change them in flight anyway.

 

Thanks for your reply Jordan that's what I wanted to know if the weather changes why should you

change the settings won't it affect the performance of the aircraft? fuel E.t.c.

[pcubine 143]

 

 

You wouldn't change them in flight anyway.

Jordan

 

If you had newer information from say AS2012 why wouln't you update winds at the remaining waypoints in the flight plan? I do it it in the MD-11 if there are any significant changes from what is in the FMS. On some of 10-12 hour flights I do in the MD-11 the ETA and remaining fuel at landing can go haywire real quick in the last third of the flight.

 

Michael Cubine

[Flamin_Squirrel 71]

Thanks for your reply Jordan that's what I wanted to know if the weather changes why should you

change the settings won't it affect the performance of the aircraft? fuel E.t.c.

 

During flight, the FMC takes winds from 2 sources; the forecast winds you entered into the FMC during preflight and the winds the aircraft is actually encountering.

 

Fuel and time predictions are based on blending these 2 sources of information together, with forecast winds being used for far off waypoints and actual winds taking priority as the waypoint gets closer.

[pcubine 143]

with forecast winds being used for far off waypoints and actual winds taking priority as the waypoint gets closer

 

 

Jordan

 

So you are saying if the flight plan has 15 waypoints left, the FMS is maybe only using the forecasted winds for last 10 and actual for the next 5 waypoints in calculating an ETA. I know it's not as black and white as 15/10/5 but this is the general idea.

 

Michael Cubine

[Flamin_Squirrel 71]

Jordan

 

So you are saying if the flight plan has 15 waypoints left, the FMS is maybe only using the forecasted winds for last 10 and actual for the next 5 waypoints in calculating an ETA. I know it's not as black and white as 15/10/5 but this is the general idea.

 

Michael Cubine

It might be done on distance, can't remember exactly! Using your example though, it might use actual winds for the next 5, forecast winds for the last 5, and a mix of the 2 for the middle 5. It's described in the FCOM.

[pcubine 143]

It's described in the FCOM.

Jordan

 

I see what you are talking about on page 11.42.38 of FCOMv2. When the problem with changing wind entries is corrected, I think I would still go ahead and enter any significant changes from a new forecast except for maybe the next three waypoints unless they are the start of long legs like 250-350 nm.

 

I just finished a 12.2 hour MD-11 flight and I didn't change any wind entries even though I had a newer forecast. In the first six hours of the flight the ETA was 0323Z or 0324Z. In the last six hours it went to 0345Z.

 

Michael Cubine

[Flamin_Squirrel 71]

I wouldn't bother trying to update the winds because I don't think this is done in reality, and PFPX gives me pretty accurate information in the first place.

[scandinavian13 5,192]

 

 

I wouldn't bother trying to update the winds because I don't think this is done in reality

 

Careful.

 

What one operator does, another operator will turn upside-down, repaint, re-word, and otherwise contradict the former practice.  Example: SWA didn't use A/T or VNAV until recently, while other operators did.  Some operators leave landing lights on until 10.  Some turn some of the lights off at gear retract, and the rest at 10.

 

Remember that your wind pull in the sim is current wind only.  Airline systems generally tend to have forecast winds mixed in to those data pulls to be more accurate for when the aircraft is planned to be there.  So, even if they didn't do it in the real world, you'd probably want to do it occasionally in the sim.

 

I highly doubt that pilots don't update the wind data occasionally, particularly on long segments.  Weather changes, and forecasts get less and less accurate as the time between now and the forecast increases.