FMC LEGS + RTE pages

[Hardy Heinlin]

Good morning,

is there anybody on board who can confirm the following statement on any Boeing, Airbus or similar FMS? (They are certainly identical.)

Statement: It is not possible to display RTE 1 on CDU L while RTE 2 is displayed on CDU R; if one CDU switches from RTE 1 to RTE 2, the other CDU automatically switches to RTE 2 as well.


When anybody has the time, anytime, any hint is greatly appreciated.

Thank you!

|-|ardy

[Hardy Heinlin]

Bulfer/Gifford write on page 5.8: "If the inactive route is selected on a CDU, the onside [...] map will display it in blue dashes."

Conclusion: If only the onside ND will display it, the other CDU hasn't necessarily selected it. Otherwise, always both CDUs would have the same route and both NDs would display that same route.

This independency between the two CDUs has significant consequences:

Imagine no RTE is active and CDU L wants to activate RTE 1 while CDU R wants to activate RTE 2; both CDUs have their EXEC light illuminated -- which is a common synchronized light --, but which route will finally activate would depend on which CDU will press the EXEC key first?

There might be a protection like this: If CDU L turns the EXEC light on for RTE 1, then CDU R will have no ACTIVATE prompt for its RTE 2?


|-|

[dutch57]

Hardy, goodmorning,
I can confirm your statement , about the rte activation on a cdu.

It is not the cdu who activates the route it is the fmc the cdu acts as a keybourd only.

In the FMC set-up, you have 2 FMC`s, coupled together with a data bus.
In normal operation one FMC acts as the master FMC and the other acts as a slave(following the masters).
In case of a failure the slave FMC will become the master.

So if you activate rte-1 on the lh cdu it activates, but than when you activate rte-2 on the rh cdu , than rte will be activated and tre de-activated, this is done by the master FMC

Hope this shares some light for you Hardy,

sincerly,
Bob

[Hardy Heinlin]

Hi Bob,

thank you!

Sure, I know there are 2 FMCs and that the CDUs act as keyboards. The model in PSX is extremely complex with all the CDU CBs and FMC CBs, resync timing etc., scratchpad system, menu management etc.

I just wanted to know the following:

Situation:
- CDU L displays RTE 1 page 1/1
- CDU R displays RTE 1 page 1/1

Action:
Press the prompt (LSK 6L) on CDU L

Result on CDU L:
The prompt now reads and the title reads "RTE 2"

Question:
What's the result on CDU R? Is its LSK 6L prompt and its title now identical to that of CDU L?


Cheers,

|-|ardy

[the mad hatter]

What about the forth CDU? not that it is operative from the deck as its for maintenance

see below Hardy as faster than I :-)

[Hardy Heinlin]

The fourth CDU, if installed at all, is not on the flightdeck.

I really just wanted to know if CDU L can show route 1 while CDU R shows route 2. That's all.

[the mad hatter]

Yes sir they can function independently, until failure then the master takes over
hope that helps

[Hardy Heinlin]

OK, thanks.

Actually, in the meantime, I have no design problem anymore now if two CDUs want to activate different inactive routes: The CDU which EXECs first will win.

Another problem, but also resolveable, is this:

Situation:
- CDU L has MOD RTE 1
- CDU R has RTE 2 (CDU R had inactive rte2 selected before CDU L began mod on rte1, i.e. before the

Action:
- Press ACTIVATE> on CDU R

Result:
- CDU L EXEC light is illuminated
- CDU R EXEC light is illuminated

Bizarre:
The two CDUs have no identical EXEC job. EXEC L will copy the modification to route 1 and keep that active, while EXEC R will deactivate route 1 and activate route 2.

Theory:
Pressing EXEC L will not change the display on CDU R. But pressing EXEC R will change the display of CDU L: CDU L will change from MOD RTE 1 to RTE 1. It will delete the whole modification.


|-|

[Shiv Mathur]

Hi Hardy,
I don't know how helpful this may be, or if you already found it ...
http://www.biggles-software.com/software/757_tech/flight_management_navigation/alternate_navigation.htm

From this link I quote:
"The two CDUs operate independently. A route change to one CDU does not change the other one. The route entered in the left CDU can be displayed on the captain's HSI using his NAV source select switch. The route entered in the right CDU can be displayed on the first officer's HSI using his NAV source select switch."


Cheers,

Shiv

[Hardy Heinlin]

..., until failure then the master takes over

Does that mean that an FMC can store only one route? Both FMCs must be operative to have two routes available? I can't imagine that. Route 2 would then be that of FMC R?

I think each FMC has actually 3 route memories:
- RTE 1
- RTE 2
- MOD RTE

This third route memory is necessary to keep the active route memory unchanged during a mod. Before a mod is started, the active route is copied to this third memory in which the mod is performed. Pressing ERASE will keep the original memory, pressing EXEC will copy the third route memory to the original route memory.

I'm sure this is possible also with only one FMC operative.


|-|


Edit: mad hatter, or ... by "takes over", do you mean both CDUs have identical displays when only one FMC is operative? If I press NEXT page on one CDU and it goes from page 5/12 to 6/12, the other CDU will also jump to page 6/12? (In single FMC ops.)

Edit 2: I guess in single FMC ops the page selections 6/12 ... 7/12 etc. are not synchronized between CDUs, but the route selections are. MOD and ACT title prefix and route number (1 or 2) are then identical on both CDUs.

[Hardy Heinlin]

Thank you, Shiv. That's another confirmation. Great.


Cheers,

|-|ardy

[the mad hatter]

Yes Hardy your guess is 100% correct.

The FMC  has three memories: Yes it is possible and or is supposed to be possible with single operations I have never experienced it.

In relation to edits 1 & 2 again you are correct:

I can send you the notes from when I transitioned to glass from steam in particular the FMC/CDU

Have I understood your question and answered it?

B

[Hardy Heinlin]

All answered and understood!

No further notes needed, thank you!


Ahoy

|-|

[dutch57]

Hardy,

Please bear in mind during normal operation 1 FMC is in control and the other monitors,

Entering data into Lh CDU or Rh CDU does not matter it is accepted by the master FMC and the slave FMC follows.

So activate rte-1 on the lh cdu will activate rte-1 in the FMC, activating rte-2 in rh cdu afterwards , this will activate rte-2 in the FMC.

Software wise it is not possible to have for instance rte-1 activated in lh-fmc and rte-2 activated in rh-fmc.

sincerly,
Bob

[John H Watson]

In case of a failure the slave FMC will become the master.

But this is not an automatic process. The master has to be chosen by the Master FMC Switch on the main instrument panel. At least this is the case on the 744. On the 767 (variations possible), the master is determined by the autopilot in command, the Captain's & F/O's instrument source select switches and other factors. Both are (typically) Honeywell, but they are certainly not the same in behaviour Programming can even vary on the 744 (and not only because there are different CDU types available)

The 744 Master FMC Switch determines which FMC provides EEC trimming, navigation radio autotuning and LNAV/VNAV guidance, which FMC provides A/T servo control and which provides data to the MCP for mode status and speed data.

Rgds
JHW

P.S. Bob, as an experiment, you might like to try pulling the the Left FMC CB (with the Left FMC selected as Master), with and without the IRUs aligned and see what functions remain available on the CDUs.

[Hardy Heinlin]

Hardy,

Please bear in mind during normal operation 1 FMC is in control and the other monitors,

Entering data into Lh CDU or Rh CDU does not matter it is accepted by the master FMC and the slave FMC follows.

So activate rte-1 on the lh cdu will activate rte-1 in the FMC, activating rte-2 in rh cdu afterwards , this will activate rte-2 in the FMC.

Software wise it is not possible to have for instance rte-1 activated in lh-fmc and rte-2 activated in rh-fmc.

sincerly,
Bob

Bob, thanks, that's all clear, these features have been modelled in Precision Simulator since 1996. I guess my questions sometimes sound as if I didn't know that the 747 has two wings :-) I assume my original question is still not quite understood. But it doesn't matter, it's been answered now.

[Hardy Heinlin]

What JHW wrote is also included in PSX:

In case of an FMC power loss there's no automatic switchover to another FMC nor any automatic master switching. Instead, a time-out will occur and the affected CDU will display the MENU page.

Source switching must be performed manually using the master switch and the left and right NAV source selectors.


|-|

[Hardy Heinlin]

Below: FMC R is unpowered, it's the master FMC, and both CDUs automatically jumped to their MENU:





Below: FMC L selected as master, which is the powered one, and RTE selected on CDU L:





Below: Circuit breaker of FMC R pushed in, FMC L resyncs FMC R:





Below: Inactive RTE 1 selected on CDU L, inactive RTE 2 selected on CDU R:





Below: ACTIVATE> prompt pushed on both CDUs:





Below: EXEC key pushed on CDU R:





Below: EXEC key pushed on CDU L:





Below: On CDU L destination KLAX replaced by PHNL, route 1 now in modified mode:





Below: On CDU R the ACTIVATE> prompt has been pushed:





Below: On CDU R the EXEC key has been pushed and route 2 becomes active. The modification of route 1 has been cancelled automatically, and route 1 is also inactive now.





Below: The NAV source for CDU R has been manually switched from FMC R to FMC L:





|-|

[Jeroen Hoppenbrouwers]

One more thing: I am unsure about the DSPY annunciator here. In some cases, this light is used to yell at the pilot that (s)he is watching an inactive page. Like, when looking at VNAV DES while in cruise mode, or when looking at a LEGS page not 1. Books are a bit unhelpful here, but I can imagine that looking at the inactive route is sufficient reason for DSPY to light up.


Jeroen

[Michael Stanley]

Greetings Hardy and Gentleman,
For the last 18 months I have rented my house to a 744ERF (Jade Cargo)  captain, I have  asked him a couple of the  technical questions  asked on this forum ; in this particular case his  answer was this :

"The active route (route 1) will be displayed in both NDs in Magenta.
If one pilot selects Route 2 page in his CDU, the route 2 will be displayed in his own ND only, in Cyan - if he does not press EXEC.
If the pilot press the EXEC key, then both CDUs will change to active route 2, and both NDs will display the new route in Magenta."

Kind Regards

Michael