Maximum amount of legs in CDU route memory?

[Hardy Heinlin]

Hello, does anyone know the answer?

Some airlines have installed the NG FMC in their 744 fleets. The legacy FMC can store up to 120 legs per route, the NG FMC up to 250. What did they do with their CDUs?

(A) They replaced their old CDUs by new CDUs which can store 250 legs.

(B) They just replaced the memory and software in their old CDUs to get the capacity for 250 legs.

(C) They just replaced the software in their old CDUs as they already have memory for 250 legs.

(D) They didn't change the old CDUs as they already have memory and software control for 250 legs.

(E) They didn't change the old CDUs and accept that standby navigation can operate with just 120 legs.

(F) ...


Regards,

|-|ardy

[Hardy Heinlin]

Shall we bet?

I bet it's (E).

If they had to replace the old CDUs, the new ones would now probably be LCD CDUs. But they are still green. Or are there monochromatic green LCDs?


|-|

[edoradar]

There is no SB in Honeywell database regarding modifications to the MCDUs in order to work with NG FMC. Latest SB on PN 4077880-9XX is in 2016 while on PN 4058650-9XX is way earlier. So I'd say that possible options are either to D (most likely) or A (lesser probable).

Regards

[G-CIVA]

(B) They just replaced the memory and software in their old CDUs to get the capacity for 250 legs.

From looking at the documentation I have - solution B looks like a very likely answer 

Whilst there are distinct sections in the documentation detailing the differences in system operation between the legacy & NG software I have not been able to find any reference to a newer type of CDU (other than the most up to date one in use currently) required to interface with the upgrades in memory & software.

[Jeroen Hoppenbrouwers]

(E) They didn't change the old CDUs and accept that standby navigation can operate with just 120 legs.

"Just" upgrading MCDU memory feels like such a significant mod to hardware of this class, that I believe it would require a full part number upgrade and thus a very expensive rebuild. I don't know it, I don't have access to these data, but I bet (E). "Tough for the pilots, just cope with it." When do you need this standby nav anyway?

Hoppie

[Jeroen Hoppenbrouwers]

Interesting Jeroen! I wasn't aware of all these details, and I wonder if it can't be problematic .. I mean, since this can be taillored to operator specifications, someone has to program it - can't it interfere with the overall FMC / CDU performance?

All this stuff does not sit in the FMC or CDU. Remember, the CDU is a dumb terminal head, just a keyboard and a display (if you forget about all its fancy standby stuff that only springs to life when something else fails and finally makes the CDU feel it is important).

The whole of ACARS, in Boeing airplanes, is housed in a CMU box, usually built by Honeywell or Collins. On a 777/787 it isn't a physical box any more but just an application running on the core computer rack, this time Honeywell software.

The CMU has two distinct roles.

1. Message router.
2. Message pilot interface.

The message router part talks to a few radios on the left (VHF, digital VHF, SATCOM, HF) and a few message boxes on the right (the above mentioned message pilot interface, the FMC, and sometimes an ACMS or a cabin interface). It selects the best radio, based on what works and the cheapest route, but does not create any message by itself.

The pilot interface hosts the AOC/AAC part of the system, the airline-specific stuff that can be modified by the airline within strict limits. This has the fancy menus the airline wants to do its operational and administrative things, using a server on the ground to talk to its fleet.

Normally the pilot interface also hosts the ATS part of the system, the D-ATIS and PDC and everything else that links the aircraft to the air traffic control system. In the US this is all FAA, with the network and ground servers managed by Harris. In Europe it is probably different per country.

To confuse matters, in Boeing aircraft, the FANS-1/A bit of the system (CPDLC, ADS-C) is not hosted on the CMU, but on the FMC. In Airbus aircraft, it is hosted in the equivalent of the CMU. This is just a technical choice. Either way has advantages and disadvantages.

As a general rule of thumb, if you can access it by a function key such as FMC COMM or ATC, it's hosted in the FMC, as only the FMC can respond to CDU function keys (in Boeing aircraft). If you need to MENU out to the top selection and select ACARS, it's the CMU you're talking to.


Hoppie

[Hardy Heinlin]

I too still think it's (E).

As we know, CDUs cannot store conditional waypoints. That is, CDUs are just standby navigation tools, they're not designed to provide a full backup of the active FMC route. And each CDU uses just a single IRU for position updating. An NG route may have 200+ waypoints because a higher navigation precision is required, especially within procedures, and that typically includes many conditional waypoints. If a CDU doesn't get any GPS or radio position updating nor any conditional waypoints, the CDU doesn't need a bigger route capacity either. It remains just a raw backup in any case.


|-|ardy

[G-CIVA]

E it is then. 

Or are there monochromatic green LCDs?

Choice B is your answer in your original choice of answers to this Question.  They are still 'Green Screen' with no LCD Screen upgrade or new component fit.

[ahaka]

By the way, why not replace old CRT CDUs (and other displays as well) with the newer LCD ones when they need replacement anyway i.e they break down? Isnt it more expensive to keep manufacturing old technology? I also read once from a pilot interview that the LCD ones are easier to read in different lighting conditions. Does upgrading from CRT to LCD require a new certification process?

[Hardy Heinlin]

I guess there will be a time when old defective CRT CDUs will be replaced by LCD CDUs instead of repairing the old ones. -- They've been installing LCD EFIS screens and LCD MCPs on older aircraft for more than 10 years now.


|-|

[G-CIVA]

By the way, why not replace old CRT CDUs (and other displays as well) with the newer LCD ones when they need replacement anyway i.e they break down? Isnt it more expensive to keep manufacturing old technology?

Replacement CRT CDU production probably stopped at or well before the delivery of the final 744 in 2009.

There are plenty of replacement CRT CDUs for the 744 in the spares chain from scrapped airframes to replace items that go U/S, most of the larger operators have repair facilities anyway.  Mr Boeing was never going to design & build an LCD CDU for the 744 .... I doubt any operator would want to pay for it.

The cheaper option was to take advantage of internal hardware upgrade (memory & CPU) & software upgrades utilising the in service equipment.

[Jeroen Hoppenbrouwers]

By the way, why not replace old CRT CDUs (and other displays as well) with the newer LCD ones when they need replacement anyway i.e they break down? Isnt it more expensive to keep manufacturing old technology?

When you replace any aircraft part, whether it is a lavatory sticker or an engine, with something else, that has a different part number, you need to also update the drawing of the aircraft.

To update the drawing of the aircraft, you need to develop a Supplementary Type Certificate, or pay $$$ to Mr. Boeing and get an updated Type Certificate. This is expensive no matter what you try.

The FAA needs to approve your plan, review your materials, inspect your prototype installation, and approve the (S)TC. After that your airline needs to develop new training materials, update the maintenance manuals, train pilots and maintenance engineers, update warehouse systems, keep two kinds of dissimilar stock, and roll out a complete (S)TC upgrade campaign over the whole fleet.

In the end, the price of a repair is well worth it!


Hoppie

[Hardy Heinlin]

How long do CRTs live?

[mgeiss]

Al least up to 75 years
https://www.theregister.co.uk/2011/04/04/marconi_type_702_under_the_hammer/

[farrokh747]

http://farrokhchothia.com/slists/crt/

here's a 744 cdu crt inside and out of its housing.....

fc