Minimum altitude which can be legally filed

FORANE

FORANE

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FORANE
On airways one may file for the MOCA.

Off airways is the MORA regulatory? I didn't think it was.

Is there a Minimum legal altitude for off airway flight plans? Say I am departing my home field to the North (which has a high grid MORA due to mountains South of the field). I know minimum vectoring altitude to the North of my field is way lower than the grid MORA.
 
I believe the answer is in 91.117.

§91.177 Minimum altitudes for IFR operations.
(a) Operation of aircraft at minimum altitudes. Except when necessary for takeoff or landing, or unless otherwise authorized by the FAA, no person may operate an aircraft under IFR below—

(1) The applicable minimum altitudes prescribed in parts 95 and 97 of this chapter. However, if both a MEA and a MOCA are prescribed for a particular route or route segment, a person may operate an aircraft below the MEA down to, but not below, the MOCA, provided the applicable navigation signals are available. For aircraft using VOR for navigation, this applies only when the aircraft is within 22 nautical miles of that VOR (based on the reasonable estimate by the pilot operating the aircraft of that distance); or

(2) If no applicable minimum altitude is prescribed in parts 95 and 97 of this chapter, then—

(i) In the case of operations over an area designated as a mountainous area in part 95 of this chapter, an altitude of 2,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown; or

(ii) In any other case, an altitude of 1,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown.

(b) Climb. Climb to a higher minimum IFR altitude shall begin immediately after passing the point beyond which that minimum altitude applies, except that when ground obstructions intervene, the point beyond which that higher minimum altitude applies shall be crossed at or above the applicable MCA.
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I don't see any mention of MORA/OROCA so it would seem you're within the regulations if you can assure the catch-all terrain clearances are met.

In practice I'd file the OROCA and ask for lower if I felt the need. ATC could bring you down to MVA.
 
I was thinking MVA before I clicked on it.... MOCA doesn't give you radar services many times.
 
You only FILE the legal altitude for the initial leg of the flight. I file 4000 and depending just what the off-airway routing takes me, I may given a climb to 6000 if I stray a little west into a higher MVA. What you file is what you think the legal minimum altitude would be.

OROCA is never regulatory but if you use it you'll meet the requirement of the the highest altitude within 4 NM rule. It's just likely that the actual minimum altitude would be lower for your actual route.
 
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Depending on whether or not you are in a designated mountainous area or not, you should file either 1000 feet or 2000 feet above the highest obstacle on your random point to point RNAV route +/- 4 NM to each side of the first segment centerline. Regardless of what you file, the actual altitude will be assigned in your clearance. Also remember that there is not a hemispheric rule for IFR altitudes while operating in controlled airspace, although ATC normally uses one.

I use the ForeFlight profile view with the route width set to 8 NM in my flight planning.
 
ok, from the posts so far I have a couple more questions...

How does one know if they are in a "designated mountainous area"?

If one does not have foreflight, is there another means for determining obstacles within 4 miles +/- of route centerline?

I did find the site for getting a rough idea what the FAA uses for:
MVA and MIA charts:
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/mva_mia/

For background, my airport is 0A9 Elizabethton TN.
http://www.airnav.com/airport/0A9

Grid MORA is 8600
MVA upon departure is 3600

For IFR operations we depart runway 24 and climb to 3300 before proceeding on course (though I will climb runway heading through 6000 (vector for climb) when course is to the South).:

TAKEOFF MINIMUMS:
Rwy 6,
NA-obstacles.
Rwy 24,
600-2 w/ min. climb of 380' per NM to 7000 or 3500-3
for climb in visual conditions.
DEPARTURE PROCEDURE:
Rwy 24,
climb heading
244° to 3300 before proceeding on course. For climb
in visual conditions cross Elizabethton Muni Airport at
or above 4900 before proceeding on course.


So, for a departure from my home field we will typically be West of KTRI http://www.airnav.com/airport/KTRI
over Johnson City prior to being turned on course.
Airways would provide a simple altitude. Just looking for a direct altitude to the North given MORA is 8600 and I know upon departure at least the MVA is 3600.

Thanks for the replies.
 
Here is a screenshot of a route north to Cleveland, Burke Lakefront. I would not use anything below 7000 on this route.

You would still need to depart to the West and then intercept the route after climbing.

2015-05-02 11.32.50.png
 
John Collins said:
Here is a screenshot of a route north to Cleveland, Burke Lakefront. I would not use anything below 7000 on this route.

You would still need to depart to the West and then intercept the route after climbing.

View attachment 39231
Click to expand...
That is a handy profile view.

I figured 7000 or 8000 would work depending on direction. As temps get colder and freezing level becomes a concern, perhaps airways are a better plan for me.
 
FORANE said:
That is a handy profile view.

I figured 7000 or 8000 would work depending on direction. As temps get colder and freezing level becomes a concern, perhaps airways are a better plan for me.
Click to expand...

I don't care about direction when there is icing. I ask for "wrong way" altitudes all the time during the winter to stay below the freezing level. Remember, there really aren't any "wrong way" altitudes for IFR in controlled airspace.
 
You can file for any altitude you like -- there are no rules on point. ATC will simply not clear you for one which doesn't meet the regulatory requirements. However, it behooves you to know what altitudes would be both legal and likely to be accepted in order to plan more effectively.
 
I am such a word Nazi.

Use of "which" when one means "that" is one of my pet peeves.

I need professional help. :(
 
FORANE said:
On airways one may file for the MOCA.

Off airways is the MORA regulatory? I didn't think it was.

Is there a Minimum legal altitude for off airway flight plans? Say I am departing my home field to the North (which has a high grid MORA due to mountains South of the field). I know minimum vectoring altitude to the North of my field is way lower than the grid MORA.
Click to expand...

There is no minimum legal altitude for the filing of IFR flight plans. Minimum altitudes for IFR operations can be found in FAR 91.177.
 
FORANE said:
ok, from the posts so far I have a couple more questions...

How does one know if they are in a "designated mountainous area"?

If one does not have foreflight, is there another means for determining obstacles within 4 miles +/- of route centerline?

I did find the site for getting a rough idea what the FAA uses for:
MVA and MIA charts:
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/mva_mia/

For background, my airport is 0A9 Elizabethton TN.
http://www.airnav.com/airport/0A9

Grid MORA is 8600
MVA upon departure is 3600

For IFR operations we depart runway 24 and climb to 3300 before proceeding on course (though I will climb runway heading through 6000 (vector for climb) when course is to the South).:

TAKEOFF MINIMUMS:
Rwy 6,
NA-obstacles.
Rwy 24,
600-2 w/ min. climb of 380' per NM to 7000 or 3500-3
for climb in visual conditions.
DEPARTURE PROCEDURE:
Rwy 24,
climb heading
244° to 3300 before proceeding on course. For climb
in visual conditions cross Elizabethton Muni Airport at
or above 4900 before proceeding on course.


So, for a departure from my home field we will typically be West of KTRI http://www.airnav.com/airport/KTRI
over Johnson City prior to being turned on course.
Airways would provide a simple altitude. Just looking for a direct altitude to the North given MORA is 8600 and I know upon departure at least the MVA is 3600.

Thanks for the replies.
Click to expand...

Here is a free online tool that I sometimes use for planning purposes which plots an elevation profile for a given flight path.
 
Ron Levy said:
You can file for any altitude you like -- there are no rules on point. ATC will simply not clear you for one which doesn't meet the regulatory requirements. However, it behooves you to know what altitudes would be both legal and likely to be accepted in order to plan more effectively.
Click to expand...

So if you would like to go direct, what do you use to determine the altitude likely to be accepted?

In the past I have always used either the MOCA on airways or the grid MORA as my minimum.

Looking at the link rotordude provided and flying North from my home field to an airport Northwest it shows the highest obstacle to be 3300 feet. The MVA to the North of my home field along that route is as high as 5800. So I guess I could reasonably expect to get 6000 when filing for headings 180-359?

Another issue, while I appreciate what John Collins stated about there being no "wrong way" altitudes for IFR in controlled airspace, my experience has been that controllers in my area often feel differently.
 
FORANE said:
So if you would like to go direct, what do you use to determine the altitude likely to be accepted?

In the past I have always used either the MOCA on airways or the grid MORA as my minimum.

Looking at the link rotordude provided and flying North from my home field to an airport Northwest it shows the highest obstacle to be 3300 feet. The MVA to the North of my home field along that route is as high as 5800. So I guess I could reasonably expect to get 6000 when filing for headings 180-359?

Another issue, while I appreciate what John Collins stated about there being no "wrong way" altitudes for IFR in controlled airspace, my experience has been that controllers in my area often feel differently.
Click to expand...

In practice, the lowest assigned IFR altitude for flights of any significant distance will typically be the minimum IFR altitude, rounded up to the next cardinal altitude, plus 1000 feet to allow for IFR operations at airports along the route, with possibly another 1000 feet for direction of flight. Per the FARs, there are no "wrong way" altitudes for IFR flight in controlled airspace. The hemispheric rule applies to uncontrolled airspace, in controlled airspace you fly at the altitude assigned by ATC. But Order JO 7110.65 Air Traffic Control has a hemispheric rule in the assignment of that altitude. It's not carved in stone, however, there are many exceptions that allow assignment of wrong way altitudes.
 
roncachamp said:
In practice, the lowest assigned IFR altitude for flights of any significant distance will typically be the minimum IFR altitude, rounded up to the next cardinal altitude, plus 1000 feet to allow for IFR operations at airports along the route, with possibly another 1000 feet for direction of flight. Per the FARs, there are no "wrong way" altitudes for IFR flight in controlled airspace. The hemispheric rule applies to uncontrolled airspace, in controlled airspace you fly at the altitude assigned by ATC. But Order JO 7110.65 Air Traffic Control has a hemispheric rule in the assignment of that altitude. It's not carved in stone, however, there are many exceptions that allow assignment of wrong way altitudes.
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ok
This is helpful.

I found this for minimum IFR altitude but I have a hard time making much sense of it as displayed on the link here:
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/mva_mia/mia/

FAR 91.177 as you mentioned and as posted by AustinPilot makes sense, but how exactly does one determine "the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown"?
 
FORANE said:
ok
This is helpful.

I found this for minimum IFR altitude but I have a hard time making much sense of it as displayed on the link here:
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/mva_mia/mia/

FAR 91.177 as you mentioned and as posted by AustinPilot makes sense, but how exactly does one determine "the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown"?
Click to expand...

Traditionally, one uses a sectional, plotter, and pencil. There are now some computer programs that can make finding the absolute minimum IFR altitude quite simple, but I'm not familiar with any that are available to the general public. Is that what you're seeking, the absolute minimum IFR altitude? Why?
 
FORANE said:
ok
This is helpful.

I found this for minimum IFR altitude but I have a hard time making much sense of it as displayed on the link here:
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/mva_mia/mia/

FAR 91.177 as you mentioned and as posted by AustinPilot makes sense, but how exactly does one determine "the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown"?
Click to expand...

The link I gave you does exactly that. You can set the width of the profile, e.g. 8 nm total width for +/- 4nm from center, plus the route you want to fly, and it will plot the profile. It is "not official", so you can verify it's correct by looking at the OROCA, for example, as a cross-check. The OROCA is of course coarser, and therefore likely to be higher (when used to calculate the MIA). Note also that OROCA includes obstructions, not just elevations, e.g. a tower on a hilltop. Ideally you can both plot your course using that tool (or equivalent -- e.g. your tablet may have that built-in) as well as cross-check the OROCA, if you plan a "nap-of-the-earth" IFR flight, e.g. where icing is an issue. Also, bear in mind that even if you clear all terrain and obstacles, navigation (if not space-based), radar coverage and communication might still be an issue.
 
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roncachamp said:
Traditionally, one uses a sectional, plotter, and pencil. There are now some computer programs that can make finding the absolute minimum IFR altitude quite simple, but I'm not familiar with any that are available to the general public. Is that what you're seeking, the absolute minimum IFR altitude? Why?
Click to expand...
RotorDude partially answered the why below with the icing issue. I would like to stay well below the freezing level. The other reason is the airway routes North involve a bit of doglegs I would like to avoid.

RotorDude said:
The link I gave you does exactly that. You can set the width of the profile, e.g. 8 nm total width for +/- 4nm from center, plus the route you want to fly, and it will plot the profile. It is "not official", so you can verify it's correct by looking at the OROCA, for example, as a cross-check. The OROCA is of course coarser, and therefore likely to be higher (when used to calculate the MIA). Note also that OROCA includes obstructions, not just elevations, e.g. a tower on a hilltop. Ideally you can both plot your course using that tool (or equivalent -- e.g. your tablet may have that built-in) as well as cross-check the OROCA, if you plan a "nap-of-the-earth" IFR flight, e.g. where icing is an issue.
Click to expand...

Yes, I like the link but am just questioning the accuracy of the data provided and the likelihood of getting cleared as filed.

Also, the OROCA in my area is 8600 yet MVA upon departure is just 3600 and the site you linked shows the highest obstacle along my entire route would be just 3300.

Airways MEA would be 6400 and take me well out of my way. I am just wondering if I might be able to go direct and get cleared to do it at 6000. I know the terrain along that route. I know 6000 would be a safe altitude. Just wondering if 6000 would be granted and for that matter a legal altitude (which after doing some more reading appears to be so).
 
FORANE said:
RotorDude partially answered the why below with the icing issue. I would like to stay well below the freezing level. The other reason is the airway routes North involve a bit of doglegs I would like to avoid.



Yes, I like the link but am just questioning the accuracy of the data provided and the likelihood of getting cleared as filed.

Also, the OROCA in my area is 8600 yet MVA upon departure is just 3600 and the site you linked shows the highest obstacle along my entire route would be just 3300.

Airways MEA would be 6400 and take me well out of my way. I am just wondering if I might be able to go direct and get cleared to do it at 6000. I know the terrain along that route. I know 6000 would be a safe altitude. Just wondering if 6000 would be granted and for that matter a legal altitude (which after doing some more reading appears to be so).
Click to expand...

Some more things to consider. First, OROCA includes obstacles, not just elevation, while the tool I linked reflects terrain elevations only, AFAIK (that's also true for the VFR charts MEF or maximum elevation figure). Clearly you don't want to run into antenna towers or windmill farms even if well above the terrain (and I already mentioned radar, communication and navigation issues at lower altitudes). Also, ATC will provide a wider swath of clear airspace than just +/- 4nm because they might need to vector you around traffic, or weather, and the altitude above might be occupied.
But in general, regs and formalities aside, I would suggest to not cut it too close with icing, and always leave yourself an out. I still remember an IMC flight in rain years ago with some work colleagues, where we were just skimming the bottom of the icing layer and picking up light rime (non FIKI), with high terrain below us. Not fun.
Luckily we made it over the higher terrain without too much accumulation and were then able to descend into warmer air, but I swore to never again to cut it this close.
 
FORANE said:
RotorDude partially answered the why below with the icing issue. I would like to stay well below the freezing level. The other reason is the airway routes North involve a bit of doglegs I would like to avoid.
Click to expand...

Regardless what you determine the minimum altitude to be ATC won't issue an altitude below their MIA/MVA.
 
FORANE said:
So if you would like to go direct, what do you use to determine the altitude likely to be accepted?
Click to expand...
Probably the Profile tool in ForeFlight. You could also plot it on a sectional and look for an altitude which meets 91.177.

In the past I have always used either the MOCA on airways or the grid MORA as my minimum.
Click to expand...
You mean the OROCA? Yes, you could use that, but the MOCA probably isn't going to work as it may be below the MVA, and GPS direct usually requires radar monitoring.

Another issue, while I appreciate what John Collins stated about there being no "wrong way" altitudes for IFR in controlled airspace, my experience has been that controllers in my area often feel differently.
Click to expand...
From a regulatory perspective, John is correct. However, 7110.65 tells controllers that in the absence of some letter of agreement to the contrary (more on that below), they are normally to assign altitudes based on that hemispheric rule (odd-East, even-West). However, they have latitude to allow contrary altitudes when traffic permits and there's an operational reason to do it (e.g., staying above the rocks and below the icing).

Note that in some cases, ATC has established special altitude rules for certain airways. For example, if you look at V29 starting at Snow Hill MD (SWL) and going all the way up to Watertown NY (ART), you'll see it zig-zags back and forth across the North-South line. Rather than have airplanes doing a head-to-head rollercoaster act, the ATC facilities along the route established a letter of agreement to assign North-Odd/South-Even for altitude assignments. Similar deals are in place in Florida where all the airways bend through North-South around Orlando, and in California where they bend crossing about the SF-Sacramento line.
 
Hey Ron

Is not the OROCA the same thing as the grid MORA?

Sorry if I was not clear. I meant In the past I have always used either the MOCA on airways or when off airways flying direct the grid MORA as my minimum.
The OROCA isn't very helpful when going North out of my home field as it is high due to terrain South of the field.
 
I'm not sure what a "grid MORA" is or where to find it. I know for sure what an OROCA is and where to find it.
 
Remember that the Low Altitude Enroute Charts show OROCA and the VFR Sectionals show MEF. The former includes obstacles and terrain plus 1000/2000 feet of clearance, the latter does not include the 1000/2000 of clearance. The size of the grid is different as well.
 
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