Two CDI from single nav source?

CRQFlier

CRQFlier

Pre-takeoff checklist
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CRQFlier
Looking for comments and recommendations to clarify my thinking.

My current setup is a GNC355 driving CDI #1 and an SL30 driving CDI #2.

I just purchased an Aspen E5 that has an HSI and can receive two nav sources without a switch.

Some questions:

1. Can the GNC355 drive both cdi#1 and the E5 simultaneously with no switch?

2. Can the SL30 do the same woth cdi #2?

My thinking is leave both existing CDI for redundancy as well as easy operation - perhaps ILS glideslope backing up a GPS approach, etc.

If a single nav source can't drive two indicators simultaneously, how would you configure? Ditch both CDI and only have the switchable E5 HSI? Or dedicate the HSI to the GPS and a regular CDI to the SL30 (and ditch the second CDI)?

I'd like to fly ILS with the HSI but probably not at the loss of a fully independent backup - the SL30 plus CDI.

Appreciate any thoughts. Thanks.

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I wouldn’t bother. It should be possible, but unnecessary and clunky. Unnecessary because the radio can show your course deviation on its own screen even if the Aspen fails, and the HSI is not the part of the Aspen that I have heard of failing with any frequency. Clunky because the OBS knob on the CDI will probably be useless.
 
Not sure how it was done, but my 155 Nav/Com drives both a CDI and a pointer on my Aspen.
 
Pinecone said:
Not sure how it was done, but my 155 Nav/Com drives both a CDI and a pointer on my Aspen.
Click to expand...
What happens if you turn the OBS knob on the CDI?
 
I actually do not know much about the E5, but the question did get me curious enough to pull up the install manual (I originally thought it would be like the Garmin G5 that says such connections are forbidden).
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iamtheari said:
What happens if you turn the OBS knob on the CDI?
Click to expand...

It should work fine if the CDI is a KI209 or 209A as they have a built in VOR/LOC converter and the KX155 connects to it via the composite VOR/LOC signals. IOW, the CDI internally determines the left/right and to/from based on its internal OBS in conjunction with the KX155 which provides the composite signal. With the SL30, you need to have a separate ILS/LOC converter or a built in one in the CDI and use the composite output of the SL30 so that the CDI OBS has no effect on the Aspen.
 
John Collins said:
It should work fine if the CDI is a KI209 or 209A as they have a built in VOR/LOC converter and the KX155 connects to it via the composite VOR/LOC signals. IOW, the CDI internally determines the left/right and to/from based on its internal OBS in conjunction with the KX155 which provides the composite signal. With the SL30, you need to have a separate ILS/LOC converter or a built in one in the CDI and use the composite output of the SL30 so that the CDI OBS has no effect on the Aspen.
Click to expand...
Got it. See also @asicer's post just above, which explains that the GNS family (and probably any other GPS navigator since) ignore the CDI's OBS input when you're on GPS and the Aspen ARINC 429 OBS selection is alive, but respects the CDI's OBS input when you're on GPS and the Aspen is turned off. So the behavior turns out to be sane.
 
Pinecone said:
Not sure how it was done, but my 155 Nav/Com drives both a CDI and a pointer on my Aspen.
Click to expand...
In an interesting variation (I'm not sure I like), an airplane at one of our flight schools is set up so NAV 1 - a GTN650 - feeds both GPS and VLOC data to a G5 HSI and VLOC (but not GPS) independently to the old OBS.
 
iamtheari said:
What happens if you turn the OBS knob on the CDI?
Click to expand...

It used to work fine, but installing a JPI 830, they had to swap the Storm Scope and the CDI, now it is not working properly.
 
I have a 750 and a 430 that feed GPS 1, GPS 2, NAV 1 and NAV 2 to a GI 275. The 430 also feeds NAV 2 to a Garmin 106. The 106 is not connected to the AP, though. Just a backup to the 750 and 275. Can be used for ILS approaches.
 
Thanks everyone. So I "think" I could keep both back up cdi if I'd like. Or I could ditch both as the sl30 has built in cdi indication, just no gs indication. Can't remember if my cdi #2 is a ki209 or ki207 - I'll need to find my docs. I'll review all with my shop.

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If you have nothing better to put in the physical location where the current CDI instruments are, then if it were me, I would keep them.
Until there was something else I wanted in those locations.
 
I assume the Aspen is going in the locations where your AI and HSI currently reside. Further assume that you are keeping the AI and relocating it. Are you removing the current HSI and where is the AI moving to? Will the movement of the AI impact where your two existing CDI are or do you already have open space so no issue?

Are you removing any other instruments as a result of adding in the Aspen?
 
Mongoose Aviator said:
I assume the Aspen is going in the locations where your AI and HSI currently reside. Further assume that you are keeping the AI and relocating it. Are you removing the current HSI and where is the AI moving to? Will the movement of the AI impact where your two existing CDI are or do you already have open space so no issue?

Are you removing any other instruments as a result of adding in the Aspen?
Click to expand...
The Aspen is going in place of the AI and DG. I'm removing the vacuum system so no, no relocation for the AI. I've got room to keep both existing CDI. But I'm also considering an AV30 in one of those holes for backup.

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Tom J said:
Aspen requires a backup attitude for IFR installations. I'd loose a CDI and put an AV-30 in.
Click to expand...
Backup AI not required for an E5. Though as I mentioned, I'm thinking about an AV30 anyway.

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