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GPS Overlay

I

IggyMax

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us-northcarolina
Just to clear up in my mind exactly what this is, I assume an approach labeled RNAV (GPS) is a GPS overlay for an RNAV approach. You should not need BOTH a GPS AND an RNAV approach for a runway. Is this correct ?.

ALso, as I understand it the FAA sometimes, in order to not write another GPS approach procedure for a runway, just makes a GPS overlay for a given approach. How do we tell if an approach also has a GPS overlay ?

Thanks,
Dave Hinson (IggyMax)
 
Just to clear up in my mind exactly what this is, I assume an approach labeled RNAV (GPS) is a GPS overlay for an RNAV approach. You should not need BOTH a GPS AND an RNAV approach for a runway. Is this correct ?.
Click to expand...

I believe your assumption is correct. An RNAV(GPS) is an RNAV approach. You would not need a separate stand-alone GPS approach. You could check the GPS overlay box, but this is not needed IMO. The RNAV option(s) would show up in the ATC dialogue window and be available to the simmer. You may wish to clarify in the write-up which plate this corresponds to, assuming you make your work available to others.

Appropriately certified GPS units are considered RNAV as are many Flight Management Systems. So RNAV(GPS) is an RNAV approach, which can be flown using a certified unit.

GPS stand-alone approaches appear to be disappearing - at least in the U.S. - and getting replaced by RNAV approaches. In some cases you see RNAV(RNP), which is an RNAV approach requiring special equipment on-board the aircraft.

If an airport has an RNAV(RNP) AND an RNAV(GPS) to the same runway (e.g., KLGA), I will create an RNAV for the (RNP) approach and a separate GPS for the RNAV(GPS) approach to help distinguish between the two - in this case you would not want to check the GPS overlay box in the RNAV approach as this will only serve to confuse the simmer with multiple GPS options to the same runway.

If you're uploading the work you will probably want to mention this in the write-up so simmers know which plate to use for the RNAV and the GPS approaches.
 
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If you overlay a RNAV with the GPS then the default ATC system will now always say fly the GPS approach instead of the RNAV approach.

ATC will always say GPS if it is a overlay regardless of what you are adding the overlay to. I am not sure if that is a bug in the ATC system or not. FS always seperated the default RNAV and the GPS so ATC will say the correct verbage.
 
Thanks, guys. I thought you two would respond. I enjoy reading your comments and tutorials.
 
I think GPS Overlay is a US-only (FAA TERPS) phenomenon. FAA took conventional non-precision approaches and checked to see if they could be flown with GPS and if they could, created a GPS overlay approach that could legally be flown without the navaid.

The FAA created a few pure GPS approaches, but changed policy. Now all of these approaches are listed RNAV(GPS) and can be used with either an RNAV system or GPS system, though the notes might place certain restrictions (mainly on RNAV RNP). In ICAO you will see RNAV(GNSS) meaning the same thing. Of late I only create RNAV approaches as to me it just clutters up the sim GPS scrolling through all the approaches and having the RNAV and GPS approaches duplicated.

scott s.
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