Garmin for Non-Overlay Approaches

Guest Discussion
#1

On a non-overlay approach, such as a localizer back-course, can the Garmins be used legally for waypoint reference?

For example, onthe runway 11 localizer back-course at Alton IL (ALN), which I happen to be flying this evening on some recurrent training, the FAF is determined either by a radial from the STL VOR or DME from the ILS “end” (I-ALN). I’d assume that the Garmin will track (for reference) when I come to the FAF. However, my assumption is that to be legal, I’d still have to use the VOR radial, or do a direct-to the ILS (I-ALN) waypoint if that can be done.

  1. Am I correct on this?
  2. Will the Garmins do a direct to the ILS waypoint? (On the simulator, it seems willint to do that - calls it an intersection.)

Any help and resulting avoidance of embarrasment with my instructor would be greatly appreciated.

Andy

#2

My understanding of the regulations is that as long as the fix is in the GPS database, The GPS CAN substitute for DME. So in your case, as long as the DME fixes are published in the Garmin database, the Garmin IS approved to determine that fix on the approach. But the localizer still has to flown tuned to its frequency on VLOC.
Brian

#3

Andy, If, and only if Eldon, Squar, and Keels are in the database can you use GPS to identify them. I would be very surprised if you can find the I-ALN 2.0 or 0.5 mile fixes as the location of the localizer is NOT in the database.
Therefore you would be limited to a MDA of 980.
This type of approach is perfect for the bearing function of the Sandel. Set the number one radio to the localizer and the #2 Nav radio to STL. Show the bearing pointer for #2 on the Sandel and read off 057 and 073 when you get there. It’s all on one instrument.
About the DME non named fixes though I think you’re out of luck.

#4

Andy, If, and only if Eldon, Squar, and Keels are in the database can you use GPS to identify them. I would be very surprised if you can find the I-ALN 2.0 or 0.5 mile fixes as the location of the localizer is NOT in the database.
Therefore you would be limited to a MDA of 980.
This type of approach is perfect for the bearing function of the Sandel. Set the number one radio to the localizer and the #2 Nav radio to STL. Show the bearing pointer for #2 on the Sandel and read off 057 and 073 when you get there. It’s all on one instrument.
About the DME non named fixes though I think you’re out of luck.

#5

Brian, are you saying that the “reference overlay” is legal to determine the FAF, or do I have to do “direct-to” I-ALN and note the distance? (The latter could be done on Garmin #2 if necessary)

Andy

#6

< Therefore you would be limited to a MDA of 980.

That’s not the way I read my Garmin manual. Since the 900 foot step is 2 DME from the localizer (2.1 DME from the runway missed approach point), you could descend to 900 at 2.1 from the missed approach.

#7

Andy:
I do not have the advantage of having the specific approach plate as a reference. But if the FAF on this approach is a named fix and that fix IS IN the GPS database, then GPS CAN be used to legally identify that fix. The WHOLE approach requires a localizer frequentcy to legally fly the approach so you cannot use GPS alone to fly the approach. But using GPS to indentify any fix in the database on or off the approach is very legal.
Brian

#8

Art, I admit you are correct. The AIM gives the option of using a named fix as the waypoint. Since the MAP RW11 is named you can use it to determine the 2.0 DME stepdown fix (it is 2.1 miles from the MAP).
I stand corrected.