B744 Dual FMC Failure

[an3_bolt]

Just a couple of quick questions that someone might be able to help with:eek::

1. With a dual FMC failure on the 400 is it RNP capable?
2. Is there any method to use the GPS for map information / or is it solely respective IRS info?
3. Maxmimum time available without position updating ? (I take it is no longer able to update as it is solely IRS without triple mixing or other)
4. I understand that it is no langer Cat 3 capable - but if only a single FMC failure I had some notes stating that it is necessary to manually tune the centre ILS - is this in fact true and the reasoning behind it?
5. How far and what would you do in the case of a double FMC failure?

Thanks for any assistance/knowledge that can be provided.

[cosmiccomet]

According to my books, two IRS in conjuction with one FMC system and two CDUs meet the inertial navigation system requirements of FAA Advisory Circular 25-4 for flights up to 18 hrs.

So I don't see the B744 higher than RNP-10 with dual FMC failure.



About having to manual tune the center ILS in case of a single FMC failure, I could find nothing about it.
In case of a dual FMC failure, you have to manually tune the ILS in the three CDU's.

For dual FMC failure, the MAP mode of the ND could be use, but it is only gonna display the store waypoints in the ACTIVE flight plan at the moment of the failure.
New waypoints can be entered but in Latitude/Longitude form.

[NSEU]

but if only a single FMC failure I had some notes stating that it is necessary to manually tune the centre ILS - is this in fact true and the reasoning behind it?

Normally the Master FMC tunes all 3 MMR's ("ILS receivers" for older folks like me) via either Captain's or F/O's CDU entry (or via autotune). When the pilot makes a frequency/course entry in/on the CDU, the CDU then sends this info on a databus to the FMC which then sends tuning data to the 3 MMR's on other databusses.

If the FMC's are dead, there are backup databusses directly from each CDU to their respective MMR's (i.e. Left CDU feeds Left MMR, etc). To tune all three receivers, you have to make 3 individual entries (Note: with this method, it is possible to put 3 different frequencies into the receivers, so take care).

You can simulate this by pulling the Left and Right FMC (computer) circuit breakers (the ALTN Nav Radio page will appear on the pedestal CDU when you push the NAV RAD key).

http://www.ozemail.com.au/~b744er/ALTNNavRadCentreCDU.jpg

Re Map data... Normally the map displays are fed by their respective FMC's (for position data). However, the IRS's will run the ND's without FMC input.

If I recall correctly...

Only the FMC can be updated by GPS, etc.. so you are left with raw IRU data

The data for each ND will be onside IRU data... i.e. not mixed).

Hope this helps
Rgds.
NSEU

[Silent Running]

As Per Our Current Ops.

1. No (Must be able to couple available navigation system to Autopilot and -400 will have only HDG/ALT functions available to A/P with dual FMC failure)
2. Only respective IRS info available to MAP (I stand to be corrected by anyone who knows better)
3. Updating is only available to the FMC not the IRS
4. CAT 3A ie. LWMO ops without requirement for autothrottle IS available with dual FMC failure
5. Depends where you're going... basic autopilot modes are available but no autopilot NAV coupling except for APR. No RNP available either so remove newspapers and plug in junior crew member to monitor TRK offset and HDG functions.

Hope that helps:)

[an3_bolt]

Thanks guys - appreciated. Is the type of stuff I was after as our manual are very thin in this area.

I imagine that each company has different Cat 3 requirements - ours specifically states that autothrottle (ie 1 FMC) must be operable for Cat 3 (a or b) ops - with the provision that below alert height (100' RA) the landing may be continued if autothrottle failure occurs.

Thanks everyone for filling some holes.

Cheers