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dupomar

PMDG 747-400 IRS alignment help

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I know that the way to align the IRS is to turn the knobs to align, enter the IRS set position in the FMC, wait until the "Time to Align" counter passes 1 minute, and then turn the knobs back to "Nav". When i do this however, my navigation display does show me my heading and has the word "map" in the center in yellow. The attached picture shows this. Also my attitude indicator will dissappear. If noone knows how to fix this, can someone tell me how to change the IRS align time so that it will be instant?

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Turn the knobs straight to NAV, and if I remember correctly you have to enter the position twice in the 747. The alignment time settings are in the PMDG menu under the "add-ons" section of the menu bar.


Shane Gavin

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There are three ways to align the IRS system:

 

Full Alignment: Move IRS mode selector from OFF direct to NAV and enter position in FMC. This takes about 10 minutes. Recommended for every flight, or at least every 18 hours, or for flights over areas of unreliable or no radio updating.

 

High Latitude Alignment: Move IRS mode selector to ALIGN and enter position in FMC. This take approximately 17 minutes. After 17 minutes, move the selector from ALIGN to NAV. Recommended when departing polar regions. (Provides additional time to measure earth's rotation rate which is extremely slow at high latitudes.)

 

Fast Alignment: IRS must already be aligned. Move IRS selector from NAV to ALIGN and back to NAV. Position entry is not required to complete the alignment, but would improve accuracy. Takes about 30 seconds. Not recommended for flights over areas of poor radio updating. Does not provide accuracy of Full Alignment.


Devin Pollock
CYOW

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but i thought that the knobshave to be turned to "align at some point" at which point is this. Would i be correct in saying

1. turn knobs to align

2.enter position

3wait until alignment is complet

4. turn knobs back

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Nope. From OFF, you move them directly to NAV, enter the position in FMC...takes about 10 minutes.

 

During a Full Alignment, the IRU detects a new reference latitude and reference true north by sensing the rotation of the earth. All update bias and internal velocities will be reset to zero and a latitude/longitude comparison and a sine/cosine latitude test will be performed. A new initial position will be defined.

 

The only time you would use ALIGN is in polar regions where the rotation of the earth is much slower, thus allowing additional time for the IRU to measure the earth's rotation rate. In this situation, you would use the "High Latitude Alignment" method explained above. (I'm not sure if this is modeled in PMDG's simulation...I've never tried it.)


Devin Pollock
CYOW

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so after 10 minutes have passed, would i be done or is there a step after that?

 

In response to AudioHavoc's answer, where is this pmdg menu bar? Is it in FSX, there website, a program that i got when i installed the 747?

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This is from PMDG itself:

 

http://support.preci...gn-the-irs.aspx

 

Here's the basic method:

  1. Move the IRS selectors from OFF to NAV
  2. Open the FMC and go to the POS INIT page, downselect the GPS Position into the ENTER IRS POS prompt (LSK 6R).
  3. Wait the specified time (set in the PMDG/General/IRS dialog) - a countdown is visible in the upper left corner of the ND.
  4. IRS alignment is complete when you have a full PFD and ND displayed.

If you see the ENTER IRS POS prompt twice

 

This is a feature of the real aircraft's IRS and happens because the plane has been moved from the IRS's last known position while the gyros were powered down. In FS this can happen easily if you start your next flight after a shutdown from a new airport or gate location. The FMC will ask for the current position twice just to make absolutely sure that it's accurate.

 

Nothing more, nothing less. If you can't get the displays to come up, you're missing a step.

 

I suggest using this tutorial:

 

http://smithplanet.com/fs2004/pmdg/

 

When you get to his part about aligning the IRS, don't move it to ALIGN like he says, but just leave it at NAV. Follow his steps for entering the position in the FMC. If you follow these steps, you will get your displays once it's aligned.


Devin Pollock
CYOW

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I don't get it KMerchak. You did up a 2 year old post, quote a comment but don't add anything to what you quoted?


Avsim Board of Directors | Avsim Forums Moderator

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I don't get it KMerchak.

 

Some users just like to bring up old posts :P


I7-800k,Corsair h1101 cooler ,Asus Strix Gaming Intel Z370 S11 motherboard, Corsair 32gb ramDD4,    2  ssd 500gb 970 drive, gtx 1080ti Card,  RM850 power supply

 

Peter kelberg

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Just wait till they bring up posts from 2006!!  It has been known to happen.  AVSIM needs the auto lock on old posts!  Easier to post a new topic...


Brent Lewis

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I guess this one can R.I.P.


Regards,

 

Dave Opper

HiFi Support Manager

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