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2 Answers

Direct to ILS IAF on the G1000

Asked by: 801 views Instrument Rating

Let’s say you wanted to shoot the ILS 16 at KMCC. Approaching from the northwest you are cleared for the approach direct to DASHE. When are you supposed to switch to the localizer?

It would seem to me that if you switch before reaching DASHE you have no way of legally flying the direct course. If you switch after reaching DASHE you are using GPS to follow the localizer course for the few seconds it takes to switch, also not legal.

 

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2 Answers

  1. Best Answer


    John D Collins on Jul 08, 2023

    You wrote:

    \”It would seem to me that if you switch before reaching DASHE you have no way of legally flying the direct course. If you switch after reaching DASHE you are using GPS to follow the localizer course for the few seconds it takes to switch, also not legal\”

    I disagree with your conclusion. Although AC 90-108 says: “Lateral Navigation on LOC-Based Courses. Lateral navigation on LOC-based courses (including LOC back-course guidance) without reference to raw LOC data”, this is not regulatory and will be clarified when AC 90-108 is superseded by AC 90-119 (only draft form now). The AFMS limitations section 2 is regulatory and Garmin uses wording such as the following that does not prohibit GPS to be used on a localizer course other than for the final approach segment: “When using the Garmin LOC/GS receivers to fly the final approach segment, LOC/GS navigation data must be selected and presented on the CDI of the pilot flying.” By not prohibiting GPS guidance to be used for lateral guidance on segments other than the final approach segment, it is allowed.

    You can switch to the localizer for lateral guidance anytime after DASHE but prior to WOODO, which is the FAF. If you are going to use the autopilot to fly the approach, I would expect the G1000 to switch to VLOC after reaching DASHE.

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  2. Mark Kolber on Jul 09, 2023

    In addition to John’s explanation, notice that if you have a GPS that automatically switches the CDI, it switches to VLOC when the leg to the FAF becomes active. That’s made to be compliant with the requirements and it’s what I do when switching manually.

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