MEA and MOCA?

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mxalix258

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mxalix258
I'm having trouble finding the point of a MOCA, I know what the definition is - but what point does it actually serve? When would a MOCA be relevant and get assigned/used?

Thanks!
 
I'm aware of the definitions...I want to know how MOCA is used in practice.

I understand better with practical examples vs. textbook definitions.

Thanks!
 
MOCA will provide obstacle clearance but wont guarantee reception. If you're GPS'in it, it is generally a non-issue.

So, the benefit is, you can fly lower than the MEA. For separation, or maybe you want to remain in the IFR system but there is IMC at MEA but clear at MOCA.
 
mxalix258 said:
I'm aware of the definitions...I want to know how MOCA is used in practice.

I understand better with practical examples vs. textbook definitions.

Thanks!
Click to expand...

MOCA is (generally) used when flying off airways.
 
MOCA is essentially an "emergency use only" altitude. Say you're on the airway at MEA and picking up ice, but you know you can get below the ice by descending just a bit more -- a lower MOCA can save the day. Yes, you may lose navaid reception, but if you have a GPS (even handheld in this emergency situation), you can stay on the airway and not crash due to the ice.

For separation purposes, ATC can assign aircraft altitudes below the MEA down to the MOCA under certain conditions:
An aircraft may be cleared below the MEA but
not below the MOCA for the route segment being
flown if the altitude assigned is at least 300 feet above
the floor of controlled airspace and one of the
following conditions are met:
NOTE−
Controllers must be aware that in the event of radio
communications failure, a pilot will climb to the MEA for
the route segment being flown.​


1. Nonradar procedures are used only within

22 miles of a VOR, VORTAC, or TACAN.
​
​
2. Radar procedures are used only when an​

operational advantage is realized and the following
actions are taken:
​
​
(a) Radar navigational guidance is provided​

until the aircraft is within 22 miles of the NAVAID,
and
​
​
(b) Lost communications instructions are​

issued.
Click to expand...


MOCA's exist only on airways, so they won't help off-airways. Ed may be confusing the MOCA with the Off-Route Obstruction Clearance Altitude (OROCA), which provides 1000 feet non-mountainous/2000 feet mountainous clearance within the limits of the lat/long box in which it is located. OROCA is useful if you're off-airways in a lost comm situation and don't have a sectional to determine the terrain/obstructions on your off-airways routing to comply with the basic 91.177 1000/2000 within 4nm minimum IFR altitude.

​
 
Yeah, I need a second Coca-Cola this morning.
 
Just reading this thread about MOCAs and seem to remember the definition mentioned something about "off-airway" so looked it up.

MOCA- The lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route segments which meets obstacle clearance requirements for the entire route segment and which assures acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR.
Click to expand...

So MOCAs are published for off-airway routes, but I don't think most of us will ever fly these routes from what I've read so far. Could be wrong on this. Anybody ever conduct operations on an off-airway route?

Back to Google.
 
over50 said:
Just reading this thread about MOCAs and seem to remember the definition mentioned something about "off-airway" so looked it up.



So MOCAs are published for off-airway routes, but I don't think most of us will ever fly these routes from what I've read so far. Could be wrong on this. Anybody ever conduct operations on an off-airway route?

Back to Google.
Click to expand...
Good catch. There are MOCA's on a few SIDs and STARs, so in that regard there are some "off-airway" routes with MOCAs. However, there are no off-route MOCAs -- that's where the OROCA comes in.
 
I want to know how MOCA is used in practice.
Click to expand...
Well, I was flying VFR one time more or less on an airway in Northern BC/Yukon mountains and ran into some heavy forest fire smoke. I'm not sure what the viz was, but I grabbed a low altitude chart and made sure I was above the MOCA! 3 miles/80 seconds or less is not a long time if a mountain pops up in front of you.
 
Ron,

Have you ever seen any of these in your travels? I'm assuming that they are for flight operations in remote areas. I found the following from a Google search, which appears to be from one of the FAA Instrument publications:

If you fly for a scheduled air carrier or operator for compensation or hire, any requests for the establishment of off-airway routes are initiated by your company through your principal operations inspector (POI) who works directly with your company and coordinates FAA approval. Air carrier authorized routes are contained in the company’s OpsSpecs under the auspices of the air carrier operating certificate.
Click to expand...



Thought I'd ask, since you probably get around more than the average individual.​
 
over50 said:
Have you ever seen any of these in your travels? I'm assuming that they are for flight operations in remote areas. I found the following from a Google search, which appears to be from one of the FAA Instrument publications:

Thought I'd ask, since you probably get around more than the average individual.​
Click to expand...
Nope. And you'd only see them if you flew for that company or were a controller through whose sector the route goes.
 
Ron Levy said:
Nope. And you'd only see them if you flew for that company or were a controller through whose sector the route goes.
Click to expand...

Like Special Use Approaches. Unless you work for the company or you're the controller for that sector, you won't see them.

I agree with the emergency application of the MOCA. It's taught in the Army as an absolute minimum altitude to maintain in the event of an emergency where you cant maintain altitude. Not something that should be filed for.
 
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over50 said:
Just reading this thread about MOCAs and seem to remember the definition mentioned something about "off-airway" so looked it up.



So MOCAs are published for off-airway routes, but I don't think most of us will ever fly these routes from what I've read so far. Could be wrong on this. Anybody ever conduct operations on an off-airway route?
Click to expand...
I haven't, but I know about them and discuss them in my AvClicks tutorials (Chapters 6 to 10 somewhere, I forget).

They're requested by air carriers, may exceed controlled airspace, may be based on private NAVAIDS, yet they meet TERPS criteria. They're unpublished, too, unlike company-requested "Direct routes" which are published in Part 95, remain within controlled airspace and are available to the general public.

My tutorials also discuss substitute routes. I try to cut to the chase.

dtuuri
 
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mxalix258 said:
I'm having trouble finding the point of a MOCA, I know what the definition is - but what point does it actually serve? When would a MOCA be relevant and get assigned/used?
Click to expand...

The MEA assures terrain/obstruction clearance, NAVAID reception, and communications. The MOCA assures only terrain/obstruction clearance beyond 22 miles of the NAVAID. Aging VORs present reception issues and have pushed MEAs up, but with GPS and direct pilot/controller communications it's not much of an issue operationally. That's why you see MEAs with a G suffix on some airways. Operation below the normal MEA requires GPS, but you have reliable communications with ATC down to that altitude.
 
I believe that certain airlines had special authorized routes in Colorado to get to ski destinations. I'll have to ask a friend.


over50 said:
Ron,

Have you ever seen any of these in your travels? I'm assuming that they are for flight operations in remote areas. I found the following from a Google search, which appears to be from one of the FAA Instrument publications:




Thought I'd ask, since you probably get around more than the average individual.​
Click to expand...
 
Velocity173 said:
Like Special Use Approaches. Unless you work for the company or you're the controller for that sector, you won't see them.
Click to expand...

One downside of the switch from paper charts to electronic. Line pilots would happily toss ya a copy of the things after they expired, if you showed an interest in seeing them.

Not suitable or appropriate for you to use, but interesting to compare their approaches to the ones the regular folk fly.

Or to peek at the crazy ones, like Rocky Mtn had built for the Dash-7...

They were just headed for the trash at every chart cycle renewal anyway...
 
jonnyjetprop said:
I believe that certain airlines had special authorized routes in Colorado to get to ski destinations. I'll have to ask a friend.
Click to expand...

Ironic. I just mentioned them.

Rocky Mtn had a private MLS (Microwave Landing System) or two, and approaches to Avon STOLport that were quite entertaining to look at.

They also had different minimums into some other airports that only qualified and tested crews could fly.
 
The best mnemonic I have found is to memorize MOCA as having the asterisk next to it. That's the splat that your plane will make if you don't obey the MOCA.

The "O" is for obstacle.
 
roncachamp said:
I've yet to encounter an off-airway MOCA.
Click to expand...

It a planning thing. You want to go across the grid with GPS but don't want to hit a freaking mountain. File MOCA plus to be assured not to die.


Or like someone said, (Ron probably) in an emergency dive down to MOCA plus. There you go. You just encountered an 'off-airway MOCA'.



....don't be mad with me. I've had a couple.
 
Headspace said:
The best mnemonic I have found is to memorize MOCA as having the asterisk next to it. That's the splat that your plane will make if you don't obey the MOCA.

The "O" is for obstacle.
Click to expand...

Heh. I like the splat thing. That's a fun way to remember it. ;)
 
Captain said:
It a planning thing. You want to go across the grid with GPS but don't want to hit a freaking mountain. File MOCA plus to be assured not to die.


Or like someone said, (Ron probably) in an emergency dive down to MOCA plus. There you go. You just encountered an 'off-airway MOCA'.



....don't be mad with me. I've had a couple.
Click to expand...

MOCAs, where charted, are part of the Part 95 airway.
 
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