New to GPS approaches; where's the MAP for this one?

[Snakum]

I've never flown aircraft with an approach-certified GPS and am just now learning GPS approaches. It has been pretty straightforward so far, and the Garmin 430 has spoiled me silly. However ....

Look closely at the profile for this linked approach plate. Where in the name of Wide World of Sports is the MAP?

http://www.activesolutions.com/thichminhthong/images/hbi_GPS3.jpg


Minh

 

[bender]

Where in the name of Wide World of Sports is the MAP?

The GPS identifies where the MAP is and will sequence you there from the previous waypoint. In this case you would probably be sequenced from Gabne to "2.5 nm from Rwy 03" and then from "2.5 nm from Rwy 03" to the MAP, but the 2.5 nm point might not be in the database.

 

[Mmmmmm Burritos]

The MAP is the runway (RW03) However if you are over the runway at the MDA of 1320 (that's 653 AGL, almost pattern altitude!) you will probably not be able to descend and land using "normal maneuvers" - depending on what you're flying of course! That is why the 2.5NM to RW03 point is there - it's a VDP (visual decent point). Look them up and learn about them, they are becoming more and more abundant. Basically it's the point where you should go missed otherwise you wont be able to maintain a normal glidepath down to the runway. Again, much more important for a jet than for a 172.

 

[wheelsup]

What you're looking at is a new-fangled GPS approach with a vertical profile (i.e. DA/DH). Basically an ILS but using the GPS to figure out the lateral and vertical guidence instead of a ground-based navaid.

Buritos, the MDA for the approach would be 1520' for a straight in CAT A airplane. What you're looking at (1320') is the DA for the vertical path if you are equipped to use it.

The reason the MAP isn't published is for this reason - check out this approach.

If you were to shoot the FMN ILS-25 (primary approach depicted) you'd go to DA, right? And then go missed. Same thing for Snakum's example - the primary approach depicted is the psedo-ILS. Shooting the GPS 3, if you're equipped to follow VNAV GPS guidence, you can go down to the DA and then go missed, which is what is depicted on the chart.

What if you were shooting the ILS in the FMN-25 approach but wanted to circle? You'd ride the GS down to the the circling MDA (6000' for CAT A aircraft) and plug away till hitting the MAP (1.1 miles from IFMN). But of course, its not depicted on the plate but it's what you'd do.

So, in the GPS 3 example, you'd decend to your MDA of 1520' and plug away till you hit the MAP, which is named RW03. This waypoint will be in the database. It's not depicted, but its what you'd do.

Hope that helps.

~wheelsup

 

[Snakum]

So I should go missed at the VDP (2.5 DME indication from threshhold)? Or is there some other indication I should be looking for on the 430?

I love GPS approaches ... brainless practically (but this one was weird) ... can't wait for WAAS.


Minhji
(Didn't see Wheel's post ... reading it now)

 

[Snakum]

So, in the GPS 3 example, you'd decend to your MDA of 1520' and plug away till you hit the MAP, which is named RW03. This waypoint will be in the database. It's not depicted, but its what you'd do.

Ahhh ... very informative. Thanks all!


Minhberg

 

[wheelsup]

So I should go missed at the VDP (2.5 DME indication from threshhold)? Or is there some other indication I should be looking for on the 430?

Minhji

You'd go missed crossing the RW03 waypoint. That will be contained in the GPS database, and you'll see it flashing up on the screen with a count down distance from it. I haven't flown a GPS approach in over a year, but from what I remember after crossing the MAP (RW03 waypoint) the GPS won't sequence to the next waypoint automatically. You'd get a to/from flip on your OBS/HSI and the distance from RW03 would start to increase again. That's how you know you've crossed the MAP with GPS. Atleast, from what I can remember!

What buritos was saying is that you can EXPECT to go missed if you don't see the runway by the VDP, because after the VDP its very hard to adhere to 91.175 - as you know one cavet is that you have to make a "normal decent to landing". If you break out over the threshold at 700' agl, its a bit hard to comply with this. For light GA aircraft it might not be such a big deal, but the bigger the plane the harder it would be to comply.

~wheelsup

EDIT: Didn't see your additional post...lol.

 

[Snakum]

Cool ... thanks guys.

I'm really going to miss NDB approaches.

Minh

 

[wheelsup]

The Garmin 430 doesn't have the problem that the Bendix stuff does. I agree, it can get confusing but the Garmin 430 can 'think' for itself (as far as I remember). I remember it being able to determine the position and that the aircraft is heading outbound and not inbound, and as such it won't sequence the waypoints.

FYI, I'm pretty sure you can switch to leg mode inside of 2 miles. However, the "ramping down" of the sensitivity happens quicker and you might go full-scale deflection, which is why they say to do it prior to 2 miles.

~wheelsup (eh?)

 

[Mmmmmm Burritos]

Buritos, the MDA for the approach would be 1520' for a straight in CAT A airplane. What you're looking at (1320') is the DA for the vertical path if you are equipped to use it.

Oops, yeah I meant that. That's what switching back and forth quickly between two web pages will do to you.