Distance Measuring Equipment

[Singlecoil]

Singlecoil,

Interesting. But please note on "the new policy, section the note: POI must approve. Good luck on getting them to sign off on anything except their paycheck.

So true. At the last two 121's I've worked for, we had approval to substitute GPS for inoperative VOR's or NDB's. We could even depart and fly a turn procedure that was based on an inop navaid as long as the GPS worked. We could even do an ILS if the compass locator outer marker was out of service when the missed approach had you turn around and hold at the LOM! It is possible to get that approved, maybe you can take that to an appellate court (his boss). The fancy stuff requires dual GPS systems, but a DME? FERCHRISSAKE! I have been under the impression that the feds were supposed to be encouraging this type of thing so they can eventually phase out the NDB's and VOR's. Of course, ask 3 different feds the same question, you will get three different answers, and fingers pointing three different ways.

 

[100LL... Again!]

Flychicaga-

There might be a couple things happening here.

I'm not 100% sure that I understand your question, but I'll take a stab at it.

If you are flying the VOR approach using the GPS for DME, load the VOR as the waypoint, and use it like traditional DME. The slight difference due to slant range is MORE than made up for by the fix displacement error calculation built into the approach. Ignore charted fixes names. Just use the raw mileage.


Now, if you are flying the GPS overlay, you are supposed to disregard the numbers and fly the fixes. The fixes are directly on top of each other. No slant range error at all. Pure lat/long.

Are you 100% sure that the GPS puts a fix at the runway end?

If it is there, the reason the GPS version has it is to allow a more accurate final appch course.

Which GPS are you using? I'll try it in demo mode on mine.

Is there a stand-alone GPS approach for that runway?

 

[midlifeflyer]

Using a slant range of 2.7 DME at 1400 MSL (651 AGL) and running the math yields an across the ground distance of 2.6979 nautical miles.

What is the formula that you used?

 

[Wiggums]

Anyone know any good reference books out there for GPS, especially the 430? The AIM just seems way too foggy on a lot of this stuff.

A good referance for the Garmin 430 is the acutal manual for the unit. If you go to garmin's website you can download the manual, and the simulator for free.

 

[midlifeflyer]

What is the formula that you used?

Never mind. I had it, just screwed up the entries.

 

[Illini Pilot]

i can vouch for what FlyChicaga is saying, i've flown this approach many times also....

if you look at the plates, Stadi is at 2.7 DME and also 2.7 nm(listed on the profile view). the VOR is pretty much at mid field, maybe a little more past (refer to airport diagram view) and with the runway 22 being 6500 ft, that comes out the the VOR being about (reiterate the about) .7 from where the final app. crs crosses the runway(MAP for the GPS approach). this difference i presume is where the error comes in.

 

[midlifeflyer]

Basically, we figured out that to ensure you step down at 2.7 correctly from 1400 feet to MDA, you need to switch pages on the unit to show the distance to the CMI VOR. Once it hits 2.7, you can commence descent and move back to the map view.

Wow! Is this a commonly used approach (other than for training purposes)? You'd think they'd add one of those GPS-only bracketed waypoints co-located with 2.7 DME. Having to switch pages really sounds like missing the point of using GPS.

 

[cocknbull]

I talked to some Flight Check guys about this and they said to contact OK City or the local FESDO.