GPS substitute for DME for LOC Approach

[Somedudeintn]

I'm still an instrument student, but, here is an interesting one I just came across. I'm used to substituting a GPS for DME from a VOR (pull up nearest VOR page on the 430), but what about when the DME is based on the localizer signal. I was looking at this approach

http://155.178.201.160/d-tpp/1608/00218IL23L.PDF

and loaded it (well the ILS approach) into the 430 simulator to check the DME fixes, but the stepdown fixes were not in there. It appears that the only way to get the distance is to put in D-> IOXH. From there, for additional situational awareness you could put the 430 in OBS mode and put in the correct radial while flying the actual localizer signal.

What would you do if the glideslope was out and you were flying this as a localizer approach with a 430 substituting for your DME?

 

[ARFlyer]

You can do it that way or go to the nearest page and select over to fixes. Once you get close enough IOXH will start appearing in the list.

If it won't let you select the LOC on the GPS for the overlay then your -D-> idea is the best. The nearest page will work in a pinch. Just shoot the approach like a normal non precision just using the 430 distance.

 

[mondtster]

I haven't flown this approach and don't have a simulator, but I seem to recall that if you load and activate the approach that the fixes will sequence as you fly the approach and you'll see the distance to the next fix. Seeing only the distance to the next fix won't really tell you the distance from I-OXH but using that method seems to be acceptable for the examiners around here.

 

[fiveoboy01]

Did you try loading the LOC 23L into the 430 instead of the ILS to see if the stepdown fixes appeared? Maybe they're on the profile view of the plate but would only show up on the GPS if you loaded the localizer approach.. seeing as how you've got the glideslope with the ILS approach and those stepdown fixes aren't needed after the FAF....?

 

[MAKG1]

I loaded the approach into my GTN sim 'cause that's what I have handy. The database should be identical.

While the plate says ILS or LOC, the database has separate ILS and LOC approaches. If you want to fly the LOC, load the LOC and all the stepdowns are there.

If you lose the GS, it's just as easy to switch the approach as it is to punch in a direct-to. And you should be able to activate the LOC and fly the ILS, since you aren't using the GPS for guidance after the FAF, and the NAV receiver won't know the difference.

 

[TheGolfPilot]

I think your problem is that you are hitting the vectors to final button. That will just make a line off of the FAF and non of the other waypoints will be on there. Activate the approach from a further out waypoint and you will see everything on there.

The GPS replaces the need for the DME because it can identify those fixes. You don't have to see the number 7.2 when you reach RKYTP, you know you are there. the 7.2 is there so people can identify RKYTP when they don't have a GPS that identifies it for them.

Remember, you must set your cdi to loc, the GPS can be used for distance information only.