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Paul12

IRS Display Question

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I go to an airport,then I disconnect the two GPS and try to modify (change ) the IRS data
using the IRS display.

In the IRS display I switch from NAV to ALIGN,when the lights finish flashing I
enter the new coordinates using the IRS display and press ENT.

In Pos 1/4 I then notice the entered coordinates ( see attached Pic1 )
In Pos 2/4 there are still some IRS data and the question is:

How can I transfer the coordinates from Pos1 to Pos2 ?

Is this at all possible ?

Thanks

HubertWerni

29w2vpw.jpg



 


Herbert Werni

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Hello Hubert,

 

What are you trying to do and why? This seems to be a very strange procedure and I fail to see the rationale here.

 

To give you a quick answer no, on POS INIT 1/4 you cannot transfer from 1R to 2R. 1R is - as the name implies - the last recorded position, and 2R are the official coordinates of the airport, usually somewhere close to the center of the airport perimeter.

 

REF AIRPORT is used to give you a rough position situation compared to last (dont forget aircraft can be moved without being powered) and - most importantly - with the GPS receivers. In other words, there will most likely be a difference but it should be small, indicating that the GPS is working and that you are not on the other side of the planet than the one where you think you are :smile:

 

Hope this helps.

 

Ionut (John) G. Micu

Romania

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Hello Hubert! Welcome back.

 

LAST POS co-ordinates (Can't be modified) - it is self explanatory. It is the last co-ordinate position the system remembers being at. It will always be there.

 

REF AIRPORT co-ordinates (Can't be modified) - These are the airport co-ordinates for the 4 letter ICAO airport code that you enter (you've entered LSZH). These co-ordinates will only show if you enter the 4 letter code. You cannot modify these co-ordinates unless you modify the Navigation Database. You cannot do that on the NGX or the real aircraft.

 

------------------------------

 

Here https://youtu.be/1xZTIyEJ7iI is a video of me aligning the IRU's using the Supplementary Procedure - IRS Entries - Present Position Entry (SP11.3) found in the FCOMv1, starting at the bottom of page 233.

 

I chose LSZH gate A44. I have fast IRS alignment enabled in my NGX. In real life, the IRS would take a longer time to align.

 

Here https://youtu.be/d16sMILBw08 is another video, with brief explanations by another person who also aligned the IRU's using the alternate procedure.

 

-------------------------------

 

You got the IRS POS/ORIGIN DISAGREE message in the scratchpad of the CDU because the co-ordinates you entered are very different to the others.

 

Hope that helps you.


Brian Nellis

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Assuming the NG is the same as every other Boeing FMC I'm familiar with --

 

-- IRS selectors to OFF then NAV

-- On the CDU POS INIT page you will then get some boxes at 4R (SET IRS POSITION). Enter the gate coordinates from the charts.

-- The IRS will then commence aligning.

 

The keypad on the IRS panel on the overhead would generally only be used in the event of a CDU failure that precluded entering the coordinates via the CDU.

 

Hope that helps.


Simon Kelsey

sig_FSLBetaTester.jpg

 

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Before typing anything at all, click on LSK 1R to copy the LAST POSITION into the scratchpad. Use that as a guide to how the FMC wants long form Lat/Lon.

 

Sign your name to your posts, please.


Kyle Rodgers

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