Dsply Source, B737ng

[KristianNorway]

Hello chaps

Can you tell me what happens when we get the DSPLY SOURCE - annunciation on the PFD, other than the fact that we are operating on only one DEU?

The thing that I don't get is:

If one gets this above FL220, nothing happens.

If one gets this below FL220:

"the flight director pitch command bar is removed from both pilots’
displays
• the flight director pitch command bar reappears at ALT ACQ
• the autopilot engages in CWS P"

Why is this?

Thanks :ok:

[de facto]

What information are the DEU receiving and what do they do?

[ImbracableCrunk]

It seems there is a lot more to the DEUs than simply providing the diplays. There's not much info in the FCOM about the DEUs.

You'll also get EEC ALTN with a DSPLY SOURCE. There must be some deep voodoo going on.

[STBYRUD]

The DEUs dont only feed the displays, but they seem to communicate bi-directionally with the EECs, the FCCs and others... My sources apart from the FCOM dont mention much about them either. Just a couple of additional points: The onside FCC will not be able to provide pitch guidance in case of a DEU failure, also the roll guidance will be removed when the APP mode is active, the EECs go into panic mode (well, to Alternate), but instead of taking info from just one DEU they continue to operate without them in ALTN mode...