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Using OBS Mode

Printed From: Avidyne
Category: Avidyne General
Forum Name: IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
Forum Description: Topics on Avidyne's IFD 5 Series and IFD 4 Series Touch Screen GPS/NAV/COM
URL: http://forums.avidyne.com/forum_posts.asp?TID=2220
Printed Date: 26 Jun 2024 at 8:44am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com


Topic: Using OBS Mode
Posted By: SoCalIFDpilot
Subject: Using OBS Mode
Date Posted: 04 Jul 2021 at 6:35pm
Had an interesting "situation" today. I was flying with my IFR instructor. We were on a simple GPS flight plan of KCMA-FIM-KIYK. I planned it in Foreflight and uploaded it to my IFD540. No problem. Then, as we were getting close to FIM, my CFII says, "I want you to hold on the FIM 260 radial, right turns, and I want you to do it in OBS mode and just fly the needles." So, I switched the IFD from GPS to OBS mode, and set up the CDI for the hold. As we crossed FIM, the IFD reverted back to GPS mode and every time I tried to switch it to OBS, it would shortly revert back to GPS. According to the Bauer book on page 104, that appears to be normal IFD behavior, as FIM was part of the GPS flight plan, and according to Bauer, "when you reach the waypoint you are tracking to, the IFD will automatically go back to GPS mode."

So, my question is this: If I'm flying a GPS flight plan, but want to use OBS mode for a hold, for example, using a waypoint on the GPS route, is there any way to do that other than deactivating the current GPS flight plan, using OBS mode, and then reactivating the flight plan when I'm finished with OBS mode?

Help and advice appreciated. Thanks!


Replies:
Posted By: dmtidler
Date Posted: 04 Jul 2021 at 8:20pm
The basic premise of an FMS such as the IFD is that the flight will be flown per the active flight plan. OBS mode really isn't designed to be used for raw data holding over a waypoint like a pseudo VOR. OBS mode will revert to GPS upon reaching the active waypoint when using OBS mode to navigate to the active waypoint, or upon intercepting the active flight plan when using OBS mode to navigate from the active waypoint.

Provided FIM was operational, you could have "flown the needles" in VLOC. Otherwise, I believe you could have "flown the needles" by simply entering the desired hold over FIM into the flight plan. I believe most external CDI's will only depict lateral deviation from the inbound leg during holding when the IFD is in GPS mode. You instructor could then just put the IFD on a page that does not display a map to "fly the needles". 


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