430W and a GPS approach question:

[fiveoboy01]

Plate in question:

http://aeronav.faa.gov/d-tpp/1511/00245r36.pdf

Today I flew the RNAV(GPS) RWY 36 approach in to Madison after being out doing some practice holding. I was coming in from the Northwest on a 150-ish degree heading at 3500 feet. The controller instructed me direct DEKEY and advised me to do the course reversal, cross DEKEY inbound at 3000 cleared for the approach etc.

So I loaded the approach into the 430W and activated it.

Soon as I crossed DEKEY "hold teardrop" annunciated and I was basically on the heading I needed to be for the entry. The CDI screen was up and after I crossed DEKEY and the teardrop annunciation, the DTK changed to 005... I was perplexed.. switched to the map page.. the magenta line on the GPS still showed a course outbound and then a turn back inbound, and the distance counter was counting up the 5 mile distance to the turn back inbound.

Once you enter the holding pattern(IE teardrop) for the course reversal, does the GPS autosequence to the final approach course heading? I didn't expect this and was very confused by it. It worked out fine, we were VFR and I had a safety pilot and I just turned back inbound after the 5 mile mark... but I need to know how this works because it might have been a little bit disastrous if I was alone in IMC turning the wrong way...

 

[TangoWhiskey]

It did it right. Notice that DEKEY is both an IF and an IAF. You crossed it the first time as the IAF, and the "hold teardrop" was your instructions for how to do the reversal back inbound, to cross DEKEY again (as the IF this time). It will autosequence to DEKEY as the IF, with a desired track of 005 inbound to the holding fix (DEKEY). If you need to stay in the hold to lose altitude or something, you need to do two things:

A ) press the OBS (SUSP) key on the GPS to get it to suspend sequencing;
B ) tell ATC that you want a turn or two (or three or four) in the hold to lose altitude. Then, when ready to head inbound, press OBS (SUSP) again to start sequencing to the next fix again.

Inbound to DEKEY from over Morey Field (C29), I get about a 150 heading inbound, so this is similar to what you would have seen:

About 2 minutes from the holding fix, it sequences to the hold with a message about "DESIRED TRACK 002 NOW"... that's true, but you're not turning LEFT to get there, you're turning RIGHT through a TEARDROP maneuver:

At this point, even though we're still flying the same original heading to DEKEY, I can see why you're confused; the GNS430W is indicating 002 at this point, but that's the INBOUND HOLDING LEG:

You just need to know "I have a hold to fly"; the autopilot, if it has GPSS steering, will fly it correctly (the magenta line); in fact, rather than the CDI page, the map page may make more sense to you here.

Finally, here's what it looks like in the flight plan. I thought it would show DEKEY twice, once as "IA" and once as "IF", but it doesn't:

 

[fiveoboy01]

After reading through your post and giving it some thought, I think it's clear now.

I was going to whine about course guidance on the entry but now that I think about it, there doesn't need to be course guidance. Cross the IAF, turn to the heading(152 in this case assuming no wind), for the entry, and fly it outbound till the 5 mile mark, then turn right inbound and intercept the final approach course. Just like you'd fly a hold over a VOR or other fix etc...

This also clarifies another point of confusion I had in flight. The CDI was showing the airplane to the right of course, and the map page showed me to the left of the magenta line by a little bit. I now realize the CDI was simply showing my position relative to the final approach course.

Thanks for your effort there and posting up the screen shots... I have the same simulator at home and I am going to run through it just to see what happens, but it makes sense now.

I've actually flown a nearly identical approach to this at a nearby airport and it all worked perfectly. The difference... it was calm that day and I let the autopilot fly it(I have GPS steering). I probably didn't monitor the CDI screen and that's why I didn't see this but I bet the same string of events happened. Today, it was so turbulent that the autopilot was having trouble, so I was hand flying.

 

[TangoWhiskey]

Glad I could help! Your post was a good one. I think I would have been confused too, seeing the north DTK when I'm supposed to be flying the holding pattern entry that heads SE... Especially two minutes before even reaching the fix!

Working through the scenario was beneficial for me as well.