IDS Switching

[John H Watson]

A question was raised on the PMDG forum. Is it possible to display the Primary EICAS on the Inboard CRT?

My books only mention the failure of both Upper and Lower IDUs to allow the display of the Upper EICAS on the Inboard IDU). This is modelled in PSX (e.g. with the pulling of circuit breakers on the overhead panel). However, also in PSX, if you fail the Upper IDU and switch the Inboard IDU to "EICAS" and the Lower IDU to "ND". The Primary EICAS appears on the inboard IDU. The basic logic gates in the IDUs indicate it's possible, but certain failures sometimes prohibit switching. Also, I don't see the point of allowing the second scenario.

I can't remember if I checked this combination on the real aircraft. Does anyone have some sim time coming up?

Thanks!
JHW

[Hardy Heinlin]

I don't see the point of allowing the second scenario.

The following is not a proof, it's just my opinion on the design:

When the lower has an ND, one pilot selected it because he cannot see an ND on his side.

Now if the upper failed, just one side can show an EICAS display.

The deck can show just one EICAS display.

Why should this one show the secondary EICAS rather than the primary EICAS?

My point is that the primary (compacted) is more important than the secondary. You don't see the point?


Cheers,

|-|ardy

[John H Watson]

When the lower has an ND, one pilot selected it because he cannot see an ND on his side.

I think I understand your logic if the other pilot needed an ND (after the failure of his Inboard IDU) and Primary EICAS needed to be shown (after the failure of the Upper IDU). With the ND in the Lower position, both pilots can share the ND display. But do two pilots necessarily have to see an ND when multiple failures occur? During Standby ops, for example, only one side gets PFD/ND.

I was just looking at it from the perspective that the same pilot had a functioning Inboard IDU and a functioning Lower IDU. I didn't see the point of one side being able to make selections to swap the normal positions of the  displays.

Anyway, it would be good if this could be confirmed (with perhaps a video in case there are any other unknown quirks).

Cheers
JHW

[Hardy Heinlin]

But do two pilots necessarily have to see an ND when multiple failures occur?

Yes, it's the only ND on the entire deck.

2 of 6 IDUs are blank. 4 IDUs remaining:

2 PFDs
1 Primary compacted EICAS
1 ND

If that single EICAS display showed no primary engine parameters, the crew wouldn't be happy, I guess.


Cheers,

|-|ardy

[John H Watson]

Yes, it's the only ND on the entire deck.

But one ND is the same as Standby Power ops. Is the procedure during standby power ops to put the Main EICAS on the Captain's Inboard IDU so that both pilots can have an ND?

Is it better to fly with one pilot having an ND directly in front of him/her, or both pilots having an ND off to one side (with possible obscurement by flight controls)? Instrument scan for one person would be much easier with the ND in the Inboard IDU position.

[Hardy Heinlin]

When the non-flying pilot who has no inboard IDU needs an ND for FMC programming etc., it may be useful to switch the ND to the lower IDU.

Whatever they switch, I see no reason why the logic should force that single remaining ECIAS display to show the secondary EICAS instead of the primary compacted. What would be the advantage? You have all this nice flexibility, and then you would still need to switch back and forth on a busy deck to see the primary engine parameters which are absolutely essential.


|-|

[John H Watson]

I'm not so much saying that the Inboard IDU will show the secondary parameters, but that certain switch combinations may not be allowed at all (especially if two switches have been moved (crossed over) on the same side and a fault has intially forced the Primary EICAS to the lower IDU).

I am seeing your point, though. The pilot flying may be doing the physical flying, so the non-flying pilot may need to access the ND for FMC stuff. However, it still takes the ND away from the pilot-flying's normal instrument scan. If the manual switching is not instantaneous, it might cause problems. Switching may be slowed down by the IDUs having to re-recognise that the Upper EICAS is dead (?).

[Hardy Heinlin]

I'm not so much saying that the Inboard IDU will show the secondary parameters, but that certain switch combinations may not be allowed at all

You mean the ND-to-LWR switch may be inhibited in the above scenario?

By the way, for the normal IFR scan ("T"-scan) to fly the aircraft, all you need is a PFD.

[John H Watson]

You mean the ND-to-LWR switch may be inhibited in the above scenario?

Yes, but only based on "why switch when the displays are already in relatively normal positions", not on any documented logic.

By the way, for the normal IFR scan ("T"-scan) to fly the aircraft, all you need is a PFD.

That's kinda where my logic breaks down. I was assuming the ND was required to maintain a track, but I guess this could be done using the compass card on the PFD. Of course situational/terrain awareness may be degraded with the ND on the Lower EICAS.