In the latest FCOM revision under the preliminary cockpit preperation normal procedures chapter ADIRS alignment has been added. However most of the conditions remain the same except for a new line which has been added wherein a full ADIRS alignment has to be performed at airports where the latitude is within 2 degrees North and South.

Could anyone explain with a reference why Airbus has decided to add this ?

As per my company FCOM this is only applicable to certain MSNs (mainly our newest A320-251N's)enter image description here

  • $\begingroup$ Airbus may cover it in a future FAST issue, but common sense says at/near the equator full alignment is very quick, so might as well do it. Are there other operational notes? $\endgroup$
    – user14897
    Apr 4, 2021 at 11:11
  • $\begingroup$ @ymb1 nothing has been attached as a note as this got added in Jan 2021. $\endgroup$
    – Jai
    Apr 4, 2021 at 11:20
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    $\begingroup$ @JuanJimenez, 0° is the equator, poles are 90° (+/- or N/S), always. $\endgroup$
    – Jan Hudec
    Apr 13, 2021 at 5:09
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    $\begingroup$ I checked with Honeywell, the manufacturer of that IRS system. They told me that they have no clue why Airbus put that in there, as they have no such requirement in their operating handbook. They referred me back to Airbus to ask the question, but I have no contacts at Airbus. $\endgroup$ Apr 20, 2021 at 2:43
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    $\begingroup$ .Alright everyone the answer I have posted is as received by my company on raising it with Airbus. Although I don't understand whatsoever how is there excess drift specifically at these co ordinates. Any further inputs to clarify will be much appreciated. $\endgroup$
    – Jai
    Apr 28, 2021 at 17:50

1 Answer 1


SOP is modified to introduce a new condition to perform a complete IRS alignment during cockpit preparation. When departure airport is located between latitudes 2° north and 2° south, a full alignment must be done. This is to avoid excessive drift of Honeywell ADIRU Block III during the subsequent flight.

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    $\begingroup$ What is it about being within 2 degrees of the equator that makes excessive drift of the ADIRU a problem? $\endgroup$ Apr 28, 2021 at 19:52
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    $\begingroup$ @WayneConrad unfortunately thats the answer I got when raised it with my company's flight operations department who in turn raised it with Airbus. This was their response. $\endgroup$
    – Jai
    Apr 29, 2021 at 17:56
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    $\begingroup$ It seems the answer is, "we made the change because we needed to make the change". $\endgroup$
    – FreeMan
    May 6, 2021 at 17:25

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