STAR Altitudes

[MidlifeFlyer]

Practically speaking, it's actually inconsequential but I've been trying to figure it out.

For the example, take a look at the DRONE1 arrival into KORF. Here's the graphic chart and the text description. Although it works for either transition, let's use the RDU transition.

On the RDU transition, the segments from RDU to CVI shows a FL190 altitude along the segment (I'm not talking about the turbojet planning information) going down to 11,000' after CVI to DRONE.

The legend for the FAA SID/STAR charts tells us this is the MEA for those route segments. In turn, the FAA defines the MEA as "the “lowest published altitude between radio fixes that assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes.”

OK. So, according to the DRONE1 charts, there is no guaranteed communication signal, navigation signal or obstacle clearance below FL190 from RDU to CVI. After crossing CVI, it goes down to 11,000'.

Now, look at the low en route chart for the exact same route.
RDU → TYI MEA 2500'; TYI → CVI MEA 1800'; CVI → DRONE MEA 2,000'.

So, is the “lowest published altitude between radio fixes that assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes” FL190 descending down to 11,000 crossing CVI (the STAR) or 9-16 thousand feet lower (the en route chart)? Anyone have a handle on this?

 

[CoffeeIcePapers]

I don't think MEA has anything to do with communication signal, just nav signal and obstacle clearance. I have no idea why the STAR is so much higher than the low enroute.

 

[mikecweb]

This is a good one. I'm not sure. But I'll be watching this thread to see if anyone has any ideas.

 

[seagull]

I think the problem is in the legend. The people who write that are not the procedure designers. The STAR is used to transition aircraft from the enroute environment, and, while it would include the MEA limitations, it also has other constraints are required by ATC. Even the enroute chart MEA might not be as low as you can go and have all of the nav and terrain sep. If the airspace underneath is uncontrolled, that could be the driver for the min altitude.

 

[MidlifeFlyer]

I don't think MEA has anything to do with communication signal, just nav signal and obstacle clearance. I have no idea why the STAR is so much higher than the low enroute.

You're right. It's just nav and obstacle clearance. Mistyping on my part. I tend to agree with seagull that it has something to do with the legend or at least with how terms are defined, and that the minimum segment altitude (I'm using that term for this instead of MEA for the time being) . Seagull, otoh, the controlled vs. uncontrolled distinction doesn't work.

 

[seagull]

Why does the controlled vs uncontrolled not work? These days it is rare, but there are still places where the lowest controlled airspace is fairly high up. Airways are controlled airspace, so the base of the airway might be higher in some cases.

 

[MidlifeFlyer]

Why does the controlled vs uncontrolled not work? These days it is rare, but there are still places where the lowest controlled airspace is fairly high up. Airways are controlled airspace, so the base of the airway might be higher in some cases.

Because I gave a specific example, with linked charts, where the issue exists. Maybe I missed it but I don't see a controlled vs uncontrolled issue there. If you do, please point it out.

 

[Ian_J]

I think the problem is in the legend. The people who write that are not the procedure designers.

After researching a bunch of stuff thanks to this thread, my guess is that the above is probably the best guess. Flip a page or two earlier in the IAP book legend for the legend for actual instrument approaches and the description of a minimum altitude combined with a procedural track seems to what the altitudes listed on a STAR really are (or should be).

 

[MidlifeFlyer]

After researching a bunch of stuff thanks to this thread, my guess is that the above is probably the best guess. Flip a page or two earlier in the IAP book legend for the legend for actual instrument approaches and the description of a minimum altitude combined with a procedural track seems to what the altitudes listed on a STAR really are (or should be).

I like it: the segment altitude is not a MEA, it's a minimum altitude for that segment of a terminal procedure., just like any other terminal procedure. And just like any other terminal procedure, obstacle clearance is not the only consideration. In some procedures it's co-extensive with the MEA; in others it's not.

Works for me

 

[seagull]

Because I gave a specific example, with linked charts, where the issue exists. Maybe I missed it but I don't see a controlled vs uncontrolled issue there. If you do, please point it out.

Oh, I was not saying that it applied to this particular case, just that there are times (in other regions of the country) when the underlaying airspace could drive an MEA to be higher than it might be otherwise.