Minimum Altitude on STAR/ RNAV STAR chart

[John777]

Hi everyone, below is the link to Jeppesen chart KMCO COSTR THREE RNAV ARRIVAL CHART:-
http://jeppesen.com/icharts/print?job-id=20160906012205517-8921

When I went through the chart, it shows bold number(altitude) below the each arrow representing the minimum altitude for that segment of the route.

Also at some intersections, displays a text in a box mentioning about the 'expect to cross at xxxxxft'

My question is what is the main function/use of the minimum altitude for each segment of the route, and why the route contains minimum altitude if ATC expects them to cross at certain altitude?

 

[flyingron]

The altitudes along the line segments are MEAs. Just like with an airway, you aren't necessarily going to be down there. It just assures you signal reception/obstacle clearance. In the turbojets this plate is targetted at, you'll almost certainly be higher, hence the EXPECT clause.

Note there are no hard crossing restrictions on this arrival. If you're told to "descend via" you can stay as high and as fast as you want as long as you're above the MEA (and aren't busting the appropriate speed restriction for your altitude). Of course, it would behoove you to be ready to hit the speeds/altitudes you were told to expect at the various points on the procedure.

 

[Everskyward]

My question is what is the main function/use of the minimum altitude for each segment of the route, and why the route contains minimum altitude if ATC expects them to cross at certain altitude?

When it says "expect" to cross, that doesn't necessarily mean that's the altitude you would be assigned to cross. Occasionally they assign something different.

 

[mscard88]

When it says "expect" to cross, that doesn't necessarily mean that's the altitude you would be assigned to cross. Occasionally they assign something different.

....and they vector you off the arrival, then tell ya to resume the arrival.

 

[John777]

The altitudes along the line segments are MEAs. Just like with an airway, you aren't necessarily going to be down there. It just assures you signal reception/obstacle clearance. In the turbojets this plate is targetted at, you'll almost certainly be higher, hence the EXPECT clause.

Note there are no hard crossing restrictions on this arrival. If you're told to "descend via" you can stay as high and as fast as you want as long as you're above the MEA (and aren't busting the appropriate speed restriction for your altitude). Of course, it would behoove you to be ready to hit the speeds/altitudes you were told to expect at the various points on the procedure.

The STAR is RNAV itself which is using GPS, do we still need signal reception though it is coming down from the satellites?

 

[Doggtyred]

The STAR is RNAV itself which is using GPS, do we still need signal reception though it is coming down from the satellites?

In the interest of technical accuracy, and slightly pedantic nitpicking, keep in mind that RNAV is "Area Navigation" and there was RNAV in use prior to GPS. You can accomplish RNAV with a DME/DME unit like the King KNS-80 or KNS-81... or with an inertial reference unit (IRU)... or with a GPS. Area navigation (RNAV), as originally envisioned, was a method of instrument flight rules (IFR) navigation that allowed an aircraft to choose any course within a network of navigation beacons, rather than navigate directly to and from the beacons. Civilian GPS put the beacons in space, rather than on the ground.

This is an unimportant distinction when training on a single engine piston plane with a GPS in it. It may become more important when flying in aircraft with one of the alternate means of accomplishing RNAV.

So, keeping the above in mind, satellite reception is only important if you are using GPS for RNAV. Satellite reception is no factor in IRU or DME/DME RNAV. But with regards to "MEA" or other altitude restrictions, altitude might be a factor for DME/DME RNAV reception... and the arrival has been flight checked to ensure that the DME/DME equipment can use the procedure as well.

 

[John777]

In the interest of technical accuracy, and slightly pedantic nitpicking, keep in mind that RNAV is "Area Navigation" and there was RNAV in use prior to GPS. You can accomplish RNAV with a DME/DME unit like the King KNS-80 or KNS-81... or with an inertial reference unit (IRU)... or with a GPS. Area navigation (RNAV), as originally envisioned, was a method of instrument flight rules (IFR) navigation that allowed an aircraft to choose any course within a network of navigation beacons, rather than navigate directly to and from the beacons. Civilian GPS put the beacons in space, rather than on the ground.

This is an unimportant distinction when training on a single engine piston plane with a GPS in it. It may become more important when flying in aircraft with one of the alternate means of accomplishing RNAV.

So, keeping the above in mind, satellite reception is only important if you are using GPS for RNAV. Satellite reception is no factor in IRU or DME/DME RNAV. But with regards to "MEA" or other altitude restrictions, altitude might be a factor for DME/DME RNAV reception... and the arrival has been flight checked to ensure that the DME/DME equipment can use the procedure as well.

Thank you sir for your help.

 

[midlifeflyer]

I notice @Doggtyred 's explanation puts "MEA" in quotes. So do I for another reason. Although it uses the term and it is not officially defined separately, the MEAs along a SID or STAR are not necessarily the same as on an airway. They may not really be the minimum altitude for either signal clearance or obstacle reception.

Proof is easy. Look at the "MEAs" along the DRONE STAR segment from RDU to DRONE (FL190 down to 11,000) with the MEAs for the exact same route on the low altitude en route chart (2,000). This STAR is assigned to light pistons at lower altitudes.

 

[John777]

I notice @Doggtyred 's explanation puts "MEA" in quotes. So do I for another reason. Although it uses the term and it is not officially defined separately, the MEAs along a SID or STAR are not necessarily the same as on an airway. They may not really be the minimum altitude for either signal clearance or obstacle reception.

Proof is easy. Look at the "MEAs" along the DRONE STAR segment from RDU to DRONE (FL190 down to 11,000) with the MEAs for the exact same route on the low altitude en route chart (2,000). This STAR is assigned to light pistons at lower altitudes.

ok so the MEA on STAR route is different?
Then what are the criterias for assigning MEA that is different from enroute MEA?

 

[midlifeflyer]

ok so the MEA on STAR route is different?
Then what are the criterias for assigning MEA that is different from enroute MEA?

Beats the heck out of me. I came across the issue when I was assigned DRONE at 5,000 in my clearance for a flight. I was of course curious and tossed the question up for discussion at the time and have brought it up periodically in threads like this. Never got an official answer but the most reasonable sounding one (to me, anyway) is that, given SID and STAR are about traffic management, there is likely some traffic management function to the way they are assigned.

Maybe one of these days I'll get curious enough to ask the Charting Office. But for now, I just accept it as real world IFR and think of it as a Procedure Altitude (my term) ATC is not bound by.

 

[luvflyin]

Theres been controversy over this. This is what I think I know. They are there so you'll know what the minimun altitude is that you should go to on that segement. They are called MEA's but they are really not. They are often much higher than the true definition of MEA requires, that being 1000(2000 in mountainous regions) foot clearance over obstacles and NAVAID reception. Many, if not most of them are altitudes that ATC wants for traffic purposes. But even ATC assigns lower altitudes sometimes as @midlifeflyer describes above. Some of those segements on some charts also have a MOCA altitude. Some user groups, the airlines in particular I think wanted minimum safe altitudes so their pilots would have the "picture" on one Chart and not have to go look elswhere to find a minimun safe altitude to use if it was needed. Or something like that. It's kinda a mess. I think commitees are working on something to make it less confusing.

 

[Doggtyred]

From a practical standpoint, on a busy day, the STAR assigned altitudes (with the misnomer "MEA") are to proceduralize the pathways in a busy airspace.... I would expect to be at the altitudes called out, and expect crossing/departing traffic above or below me, depending on airspace design. It all fits together...

 

[midlifeflyer]

From a practical standpoint, on a busy day, the STAR assigned altitudes (with the misnomer "MEA") are to proceduralize the pathways in a busy airspace.... I would expect to be at the altitudes called out, and expect crossing/departing traffic above or below me, depending on airspace design. It all fits together...

Part of the confusion is, the MEAs are not really "assigned" altitudes either. They are not, for example, the altitudes that must be followed in a "climb via" or "descend via" instruction. Good example of this is the EAGUL STAR into Phoenix because it is loaded with altitude restrictions. Compare the altitude restrictions to the MEAs on just about any segment.

So I would not necessarily expect to be at the MEA altitudes or, based on my experience with DRONE, anywhere near them.

But I think your observation is still on point. If I had to guess at a purpose, they are reference altitudes for following the lost Comm procedures in 91.185(c)(2). And that's definitely a "pathways" purpose.

 

[Gucci Pilot]

So they can say, "Climb via the SID"

Where those MEAs are coming from has been a topic of discussion at the FAA level.