Approach Plate Question

[BuickCFI]

when looking at the ILS 27 for KHLN. there are "OM-DME" mins published.

http://www.myairplane.com/databases/.../00192IL27.PDF

i understand that OM-DME means Outer Marker-DME, but what exactly are we using to identify that point? is it just the OM or DME, i.e. 4.4 DME from HLN? Or do we need to be able to identify both the OM and DME?

[fish314]

Originally Posted by BuickCFI

when looking at the ILS 27 for KHLN. there are "OM-DME" mins published.

http://www.myairplane.com/databases/.../00192IL27.PDF

i understand that OM-DME means Outer Marker-DME, but what exactly are we using to identify that point? is it just the OM or DME, i.e. 4.4 DME from HLN? Or do we need to be able to identify both the OM and DME?

It's either one. This is a pretty common thing that you'll see on a lot of approaches. Basically all it is saying is that you need to stay at or above 5400' until you get to FERRI, but in order to descend below 5400' you need to have some way to identify that you are at or past FERRI. There must be some obstacle before FERRI that the TERPSter doesn't want you to hit. So the TERPSter says that you need to have the OM or the DME because that's how you identify that you are over FERRI.

The reason that it's not a factor on the ILS is because the glideslope will ensure that you aren't too close to the obstacle, so you don't need to be able to identify FERRI if you are following the glideslope.

[juxtapilot]

Originally Posted by fish314

It's either one. This is a pretty common thing that you'll see on a lot of approaches. Basically all it is saying is that you need to stay at or above 5400' until you get to FERRI, but in order to descend below 5400' you need to have some way to identify that you are at or past FERRI. There must be some obstacle before FERRI that the TERPSter doesn't want you to hit. So the TERPSter says that you need to have the OM or the DME because that's how you identify that you are over FERRI.

The reason that it's not a factor on the ILS is because the glideslope will ensure that you aren't too close to the obstacle, so you don't need to be able to identify FERRI if you are following the glideslope.

There are some nice smoke stacks you could hit if you decend before FERRI. They actually probably aren't really a factor, they're pretty small.

[BuickCFI]

i have seen step down fixes before, just never that had 2 ways to identify

[MidlifeFlyer]

Originally Posted by fish314

It's either one. This is a pretty common thing that you'll see on a lot of approaches. Basically all it is saying is that you need to stay at or above 5400' until you get to FERRI, but in order to descend below 5400' you need to have some way to identify that you are at or past FERRI. There must be some obstacle before FERRI that the TERPSter doesn't want you to hit. So the TERPSter says that you need to have the OM or the DME because that's how you identify that you are over FERRI.

Good explanation. It's just a normal step-down fix for the LOC-only approach. IOW, your minimums for the LOC approach are 5400, but you can go lower if you can identify FERRI.

[BuickCFI]

my mind is shot today, been staring at the computer too long which is why i asked the question