GI 275 HSI - 2 CDIs?

[midlifeflyer]

Has anyone seen a display like this? No, the second white segmented CDI is not a bearing pointer. And as far as I can tell, it's not documented in the Pilot Guide. Context suggests it might be a second nav source armed in anticipation of a GPS-VLOC switch, but I've never seen this behavior in any PFD/HSI/CDI I've seen.

 

[bbarrett]

It's the preview guidance for an approach. In the Pilot's Guide, it is documented in the "Lateral and Vertical Guidance Preview" section (page 45 in Revision E). Supposed to only come on for when a NAV-based approach is loaded and you're still on GPS guidance. Very nice when you're navigating to an approach fix to intercept the final approach course. Technically, I think the lines are supposed to be gray, not white.

 

[midlifeflyer]

It's the preview guidance for an approach. In the Pilot's Guide, it is documented in the "Lateral and Vertical Guidance Preview" section (page 45 in Revision E). Supposed to only come on for when a NAV-based approach is loaded and you're still on GPS guidance. Very nice when you're navigating to an approach fix to intercept the final approach course. Technically, I think the lines are supposed to be gray, not white.

Thank you! Mystery solved!

 

[midlifeflyer]

...and it's not limited to the GI 275, which is not a surprise. Funny...when I play with the Garmin PC trainer, I use the GDU as my PFD and never noticed it has the same option. Guess I haven't used it to "fly" anything other than RNAV approaches.

Except... It's not really a preview! In theory, it preloads the inbound course for the approach but, as far as I can tell, it doesn't. You have to tell it the VOR course. I'm not sure how useful that is for a VOR approach compared to simply flying the approach via GPS and using a bearing pointer for the raw data. Would be nice to have on for an ILS; but not a VOR