MEAs, MOCAs and OROCAs

NealRomeoGolf

NealRomeoGolf

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Still doing my self-study on IFR stuff. I have a friend out near Boise that I want to go see via my plane (from Illinois) so during IFR studying I tend to look at the low charts near Boise to see what it would take to get around the rocks.

So with that background, looking at the charts I am wanting to make sure I understand this right. Below is a section of the V4 airway. Looking at the area north of Fort Bridger the MEA is 16,000 and the MOCA is 11,700. The OROCA to the north is 13,700 and to the south is 12,600.

The MEA ensures VOR navigation capability, right? The MOCA ensures I have 1,000 foot clearance from obstacles. Assuming I am navigating via GPS, the MOCA doesn't really matter to me, right? If I wanted to fly V4 in this area at 14,000 feet that is no problem? I guess if I lost GPS right there and had to fall back to VOR navigation I could have an issue. But legally with GPS I can go 14,000 feet (heading west) the whole way along? Am I understanding this right?

I guess coming back east I could then do 13,000 and still be ok?

And no we don't need to debate IFR around mountainous terrain. This is theoretical.


MEA to Boise.JPG
 
I suggest you might find the FAA Instrument Procedures Handbook useful reading: https://www.faa.gov/regulations_pol...s_handbook/media/FAA-H-8083-16B_Chapter_2.pdf

If you're assigned an airway, you need to make sure you're above the minimum (MEA/MOCA, G-MEA) no matter what you're using to navigate.

Note the OROCA is the most pessimistic altitude within that quadrangle. Your actual off-airway altitude is based on the terrain with 4 miles of your course. Of course, very few people get out the sectionals and compute it, they just use the OROCA numbers. Some flight planners can do a better number. Usually this is only a problem when there is some uncommonly high obstruction (like a huge radio tower or aerostat or something that jacks the OROCA number way up).

In your V4 case, the 10800 G and 11700G gives you GPS minimum enroute altitudes.
 
flyingron said:
I suggest you might find the FAA Instrument Procedures Handbook useful reading: https://www.faa.gov/regulations_pol...s_handbook/media/FAA-H-8083-16B_Chapter_2.pdf

If you're assigned an airway, you need to make sure you're above the minimum (MEA/MOCA, G-MEA) no matter what you're using to navigate.

Note the OROCA is the most pessimistic altitude within that quadrangle. Your actual off-airway altitude is based on the terrain with 4 miles of your course. Of course, very few people get out the sectionals and compute it, they just use the OROCA numbers. Some flight planners can do a better number. Usually this is only a problem when there is some uncommonly high obstruction (like a huge radio tower or aerostat or something that jacks the OROCA number way up).

In your V4 case, the 10800 G and 11700G gives you GPS minimum enroute altitudes.
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Thanks. Forgot about the G numbers.
 
NealRomeoGolf said:
Still doing my self-study on IFR stuff. I have a friend out near Boise that I want to go see via my plane (from Illinois) so during IFR studying I tend to look at the low charts near Boise to see what it would take to get around the rocks.

So with that background, looking at the charts I am wanting to make sure I understand this right. Below is a section of the V4 airway. Looking at the area north of Fort Bridger the MEA is 16,000 and the MOCA is 11,700. The OROCA to the north is 13,700 and to the south is 12,600.

The MEA ensures VOR navigation capability, right? The MOCA ensures I have 1,000 foot clearance from obstacles. Assuming I am navigating via GPS, the MOCA doesn't really matter to me, right? If I wanted to fly V4 in this area at 14,000 feet that is no problem? I guess if I lost GPS right there and had to fall back to VOR navigation I could have an issue. But legally with GPS I can go 14,000 feet (heading west) the whole way along? Am I understanding this right?

I guess coming back east I could then do 13,000 and still be ok?

And no we don't need to debate IFR around mountainous terrain. This is theoretical.


View attachment 85296
Click to expand...

On the airway segements your talking about you see the blue G numbers. Those are for GPS airplanes. They are very common and they are usually the same as the MOCA. If the G numbers weren’t there you could still use the MOCA for the entire segement and not be limited to within 22 miles of the VOR if you are using GPS. There was an AC or something out about this not all that long ago. I’ll see if I can find it. As far as OROCA’s go they are not a regulatory altitude. They are just there to ‘assist’ the pilot in complying with FAR 91.177 (2) if you don’t have the means to, or don’t want to figure out exactly where you are and where the rocks are. They can be very pessimistic. Death Valley, the lowest point in the US is not that far from being in the same Grid as Mt. Whitney, the highest place.
 
Actually, the FAA says this:

OROCAs depicted on en route charts do not provide the pilot with an acceptable altitude for terrain and obstruction clearance for the purposes of off-route, random RNAV direct flights in either controlled or uncontrolled airspace. OROCAs are not subject to the same scrutiny as MEAs, minimum vectoring altitude (MVAs), MOCAs, and other minimum IFR altitudes. Since they do not undergo the same obstruction evaluation, airport airspace analysis procedures, or flight inspection, they cannot provide the same level of confidence as the other minimum IFR altitudes.​

Of course, that being said, I'm not sure what they think would be sufficient as nothing off airways is surveys to the same "standards" as the airway minimum altitudes.

The principal is largely moot for non-emergency operations. The FAA won't issue you an off-airway routing below what THEY think he MIA is and that is by and large a secret number.
 
NealRomeoGolf said:
Still doing my self-study on IFR stuff. I have a friend out near Boise that I want to go see via my plane (from Illinois) so during IFR studying I tend to look at the low charts near Boise to see what it would take to get around the rocks.

So with that background, looking at the charts I am wanting to make sure I understand this right. Below is a section of the V4 airway. Looking at the area north of Fort Bridger the MEA is 16,000 and the MOCA is 11,700. The OROCA to the north is 13,700 and to the south is 12,600.

The MEA ensures VOR navigation capability, right? The MOCA ensures I have 1,000 foot clearance from obstacles. Assuming I am navigating via GPS, the MOCA doesn't really matter to me, right? If I wanted to fly V4 in this area at 14,000 feet that is no problem? I guess if I lost GPS right there and had to fall back to VOR navigation I could have an issue. But legally with GPS I can go 14,000 feet (heading west) the whole way along? Am I understanding this right?

I guess coming back east I could then do 13,000 and still be ok?

And no we don't need to debate IFR around mountainous terrain. This is theoretical.


View attachment 85296
Click to expand...

https://bruceair.wordpress.com/2017/10/11/clearances-to-gnss-equipped-aircraft-below-the-mea/
 
flyingron said:
Actually, the FAA says this:

OROCAs depicted on en route charts do not provide the pilot with an acceptable altitude for terrain and obstruction clearance for the purposes of off-route, random RNAV direct flights in either controlled or uncontrolled airspace. OROCAs are not subject to the same scrutiny as MEAs, minimum vectoring altitude (MVAs), MOCAs, and other minimum IFR altitudes. Since they do not undergo the same obstruction evaluation, airport airspace analysis procedures, or flight inspection, they cannot provide the same level of confidence as the other minimum IFR altitudes.​

Of course, that being said, I'm not sure what they think would be sufficient as nothing off airways is surveys to the same "standards" as the airway minimum altitudes.

The principal is largely moot for non-emergency operations. The FAA won't issue you an off-airway routing below what THEY think he MIA is and that is by and large a secret number.
Click to expand...

Yeah. Like I said, assist. Pilot groups have lobbied the FAA to make them more accurate and make them ‘real’ altitudes so to speak, like MEA’s etc. Making the Grids smaller, like half the size they are, like the MEF Grids on Sectionals has been suggested.
 
luvflyin said:
On the airway segements your talking about you see the blue G numbers. Those are for GPS airplanes. They are very common and they are usually the same as the MOCA. If the G numbers weren’t there you could still use the MOCA for the entire segement and not be limited to within 22 miles of the VOR if you are using GPS. There was an AC or something out about this not all that long ago. I’ll see if I can find it. As far as OROCA’s go they are not a regulatory altitude. They are just there to ‘assist’ the pilot in complying with FAR 91.177 (2) if you don’t have the means to, or don’t want to figure out exactly where you are and where the rocks are. They can be very pessimistic. Death Valley, the lowest point in the US is not that far from being in the same Grid as Mt. Whitney, the highest place.
Click to expand...

Mt. Whitney is not the highest point in the US...
 
HIghest point in Continental US.
 
flyingron said:
Lower 48.
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In an effort to derail the conversation, my wife very recently said she doesn't understand why we call them the lower 48 when there's at least one state even lower. It really should be the Middle 48 or the Eastern 48.

Even if you're in Alaska, there are 49 lower than you.

If you're in Hawaii would you say Lower 48?

I shrugged- we just call it CONUS and ignore the fact that Alaska is part of the same continent and ignore the fact that it does stand for "Continental" but "Contiguous" would also work but isn't the official acronym.
 
AU_James said:
In an effort to derail the conversation, my wife very recently said she doesn't understand why we call them the lower 48 when there's at least one state even lower. It really should be the Middle 48 or the Eastern 48.

Even if you're in Alaska, there are 49 lower than you.

If you're in Hawaii would you say Lower 48?

I shrugged- we just call it CONUS and ignore the fact that Alaska is part of the same continent and ignore the fact that it does stand for "Continental" but "Contiguous" would also work but isn't the official acronym.
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FAA uses contiguous states all of the time. They even have an acronym for it: CONUS.

Here is one example:

https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/systemops/fs/
 
The military uses CONUS as well. And OCONUS (outside-CONUS). I remember having to attend special security briefings when traveling OCONUS even if it was only Canada.

The inane part of the OCONUS briefing was that it was classified and contained information I didn't need to know or care to know (it consisted of reading dispatches on security threats for parts of the world I wasn't going near). The other typical military stupidity is the briefing goes to great lengths to tell you NOT to let on that you have a security clearance while traveling. I noticed however that my travel orders (which I have to show to people like hotels and car rentals and such to get the government/military rate), which normally has the "security clearance held" left blank for US travel, had my clearance info on the OCONUS orders.
 
Just one Spring in Silver Spring, MD. Yep, I remember NOS and then NACO and now "Aeronautical Information Services." Administratium has a half-life of only three years. It doesn't decay, it just reorganizes. They were previously in Greenbelt and then Glendale.

It's been closer to two decades now. The FAA took over in 2000.
 
flyingron said:
Just one Spring in Silver Spring, MD. Yep, I remember NOS and then NACO and now "Aeronautical Information Services." Administratium has a half-life of only three years. It doesn't decay, it just reorganizes. They were previously in Greenbelt and then Glendale.

It's been closer to two decades now. The FAA took over in 2000.
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That's why I said perhaps. I could have looked it up I guess. I went to many meetings of the ACF there 1992-2000, when it was NOS. The gentleman who ran it (Terry Laden) wore a military uniform. He was a great guy.
 
Yep, probably the same person I met when we were in a multi-FAA office discussion about the (then) DC ADIZ. They said that they couldn't issue a chart for what was supposedly a "temporary" airspace change. I pointed out that they had in the past, they made a "purple dot" version of the WASHINGTON sectional and terminal area charts to show TFRs over various stadium for the soccer prelim rounds to the Atlanta Olympics. To their credit they said, "Hey, you're right we did. We can use that point."
 
flyingron said:
I remember having to attend special security briefings when traveling OCONUS even if it was only Canada.
Click to expand...

The best part is when your clearance level is so high that you not only have to do the briefing, but you have to fill out a day by day itinerary to include addresses and method of travel with flight/train numbers which you know is wrong or going to change and that either a) nobody will look at it or b) when somebody looks at it, it will ONLY be used against you.
 
AU_James said:
The best part is when your clearance level is so high that you not only have to do the briefing, but you have to fill out a day by day itinerary to include addresses and method of travel with flight/train numbers which you know is wrong or going to change and that either a) nobody will look at it or b) when somebody looks at it, it will ONLY be used against you.
Click to expand...
At least OCONUS I don't need a statement of non-availability.
 
Many years ago I was involved with wireline telephone companies local toll calling areas were called exchanges. Where two exchanges had a common boundary they were contiguous exchanges. FWTW. Not much, I know.
 
It's from the Latin meaning touching.
 
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