IRS MONITOR page

[Hardy Heinlin]

Moin,

the 748/744 NG FMC has got a more detailed IRS MONITOR page. There's a "REF airport" in 4L and a "parking position" in 5R.

As usual, the information in the manuals is between very vague and zero.

Does anybody disagree if I say 5R is the position where the last IRS alignment was performed? I.e. it's the start and reference position of the IRS drift data shown on this page.

The Honeywell manual shows KLAX as an example, along with its database airport lat/lon under "parking position". I think in real life it won't show any database lat/lon but the actual last IRS alignment position lat/lon.


Regards,

|-|ardy

[Hardy Heinlin]

And the illustration in the 748 Honeywell manual looks strange. For the position error rate it shows this format:

0.0nm

Other FMC versions show this:

0.0nm/hr

But the description says it's the "position error rate in nautical miles". So the description must be wrong, or the illustration should show "nm/hr". Just "nautical miles" alone says nothing about the rate.

Unlike in other FMC versions, this version also shows the groundspeed. This might be the groundspeed of the average drift during the last flight, indicated in knots -- which is the same as "nm/hr", as we know. Showing this value twice on the same page makes no sense. I think the illustration is correct, and the description contains a copy&paste mistake carried over from an older FMC version.


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[Hardy Heinlin]

I'm just realizing that the IRS MONITOR page of the older FMCs shows the same data the POS REF 3/3 page indicates, namely the groundspeeds of the three IRUs -- the only difference being the resolution and the unit: On the MONITOR page it's a tenth of a "nm/hr", and on the POS REF it's a rounded "knot".

And one more difference: The MONITOR page keeps showing the data when the IRUs are turned OFF.

But aside from that, there's no essential additional info.


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[emerydc8]

Hi Hardy,

Regarding the nm/hr question, I found an old video that I don't remember doing. Does 1:37 POS 4/4 shed any light on what you're asking?

https://www.youtube.com/watch?v=d-ySswVvz8M

[Hardy Heinlin]

Hi Jon,

thank you. No, that's clear, that's the BRG/DIST on the POS REF pages.

The only question left now is whether the "REF airport" data shown on the new IRS MONITOR page is the position where the last IRS alignment was performed. I think it is.


Regards,

|-|ardy

[emerydc8]

Okay. Maybe someone on the 748, 777 or 744 with the NG can chime in.