CFII question: teaching GPS → VLOC transitions with only one CDI (GNC 355 / single NAV)

Posted by Certain_Ad_500@reddit | flying | View on Reddit | 6 comments

Hey everyone,

I’m a CFI/CFII recently got in an airplane equipped with a GNC 355 and only one NAV/CDI source (no second CDI/backup NAV).

I’m curious how other instructors are teaching:

Getting everything properly set up prior to the approach (freqs, course, CDI source, etc.)

Managing the workload during the transition from GPS → VLOC (especially on ILS/LOC approaches)

My biggest question is how to maintain positive course guidance while switching between GPS/VLOC. And what do DPEs want to see.

Thanks everyone.

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CSRAFlightCoach@reddit

If you’re flying an AP, then swap to heading mode, change OBS to VLOC, and then back to NAV mode.

When setting everything up, I do frequencies and VLOC course while I braid the approach. Fly a heading, change to green needles and set your course. Then back to pink needles if you’re still using them for navigation.

If you’re getting vectors from ATC, I’ll swap to green as soon as I get the “vectors to final” instructions from ATC.

As do DPEs, if your hand flying just get it done safely. A student should be able to hold a heading. If you’re on AP, then making sure you’re in the right mode at the right time is critical. Check to the scoreboard, and verbally state which mode you are in and which one you are going to. Don’t let the DPE doubt that you are in control of the AP.

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Nnumber@reddit

This is what I do. Or used to do before I had auto switching available.

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TungstenPyer@reddit

Answer is in AC 90-108.

Switch from GPS to VLOC after getting established on the final approach course for a VOR approach, since the AC outlines GPS can be used to track a VOR inbound

Switch from GPS to VLOC before getting established on the final approach course for an approach using a localizer, as AC 90-108 says don’t use GPS to track a localizer inbound.

Either way, have the correct source in prior to the FAF.

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Computerized-Cash@reddit

Comply with AIM 1-2-3 and AC 91-108. Essentially, hust make sure you’re switching to VLOC/Nav from GPS at the FAF.

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Antique-Kitchen-1896@reddit

I'll explain how I was taught for what it's worth.

We go to heading or track mode on the AP. No AP I guess you are hand flying a heading for a number of seconds.

Switch source, setup, back to GPS.

Go to radios when needed.

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rFlyingTower@reddit

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