Losing DTK information during ILS approach

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   I had an IFD440 installed earlier this year.  I have my maps data block setup to display the combined TRK/DTK/CDI block.  This works perfectly during RNAV/GPS approaches.  Today I shot an ILS approach in actual and as soon as the VLOC activated from GPS I lost the DTK portion of the data block (it only displayed dashes for the DTK).  I tried this exact same approach with the IFD trainer once I got home and the issue was reproducible. Interestingly, on the trainer, if I set the single line DTK data block it provided accurate heading information, it's just the DTK as part of the combined TRK/DTK/CDI that loses information in VLOC (during and ILS).
I rely extensively on the match between TRK (track) and DTK (desired tract) during instrument approaches and so I was curious if there is an explanation for this issue or if it's a known bug.

Thanks,

Russell

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ttvetdoc Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 23 Mar 2018 Status: Offline Points: 33	Post Options Post Reply Quote ttvetdoc Report Post Thanks(0) Quote Reply Topic: Losing DTK information during ILS approach Posted: 25 Nov 2018 at 3:27pm
	I had an IFD440 installed earlier this year. I have my maps data block setup to display the combined TRK/DTK/CDI block. This works perfectly during RNAV/GPS approaches. Today I shot an ILS approach in actual and as soon as the VLOC activated from GPS I lost the DTK portion of the data block (it only displayed dashes for the DTK). I tried this exact same approach with the IFD trainer once I got home and the issue was reproducible. Interestingly, on the trainer, if I set the single line DTK data block it provided accurate heading information, it's just the DTK as part of the combined TRK/DTK/CDI that loses information in VLOC (during and ILS). I rely extensively on the match between TRK (track) and DTK (desired tract) during instrument approaches and so I was curious if there is an explanation for this issue or if it's a known bug. Thanks, Russell
	SR22 - KEQY

teeth6 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 10 Mar 2014 Status: Offline Points: 741	Post Options Post Reply Quote teeth6 Report Post Thanks(0) Quote Reply Posted: 25 Nov 2018 at 9:07pm
	It’s always been that way for me too and although I like to compare DTK with TRK, I know that my DTK on an ILS is the inbound course on the Approach plate so it’s not been a problem.

AviSteve Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 12 Feb 2018 Location: Melbourne, FL Status: Offline Points: 2244	Post Options Post Reply Quote AviSteve Report Post Thanks(0) Quote Reply Posted: 26 Nov 2018 at 10:37am
	The DTK is dashed in that datablock because of the presence of the CDI. During initial certification of the IFD, the CDI and DTK were shown in that datablock. However, that was changed in response to an FAA finding during one of their evaluations. The FAA finding was that the CDI display on the IFD is always a GPS CDI, though there is nothing on the CDI depiction indicating that it is being driven by the GPS. Therefore, when the nav source is VLOC, the potential for confusion exists. In response, Avidyne removed the CDI arrow and dashed the DTK from that datablock when the nav source is VLOC. We also added a note to the Pilot's Guide specifying that the datablock CDI is always based on GPS.
	Steve Lindsley Avidyne Engineering

ttvetdoc Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 23 Mar 2018 Status: Offline Points: 33	Post Options Post Reply Quote ttvetdoc Report Post Thanks(0) Quote Reply Posted: 26 Nov 2018 at 4:12pm
	Steve, I really appreciate the reply and all the information. That makes sense and I'm glad its nothing to do with my system. I guess I can use the single line datablock DTK to display my inbound course and set that up over (or under) the combined TRK/DTK/CDI datablock. This is where a 550 would come in handy vs. my 440! Thanks again, Russell
	SR22 - KEQY