Minimum Turning Altitudes (MTAs)

HPNPilot1200

HPNPilot1200

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Jason
I hadn't heard of MTAs until recently so I thought I would post this link up here. Is there any mention of MTAs in an official FAA publication somewhere? I only found a very brief sentence in the instrument procedures handbook on page 3-9 which did not even directly describe what an MTA was.

Based on the notice below which describes some background information, it would appear that an MTA would only apply if operating at or above 10,000 feet MSL but it is not super clear on the matter. Thoughts? :confused:

http://www.faa.gov/air_traffic/publications/notices/2011-06-30/GEN11001.cfm

Here is an example from the L-4 enroute chart near Pomona, CA.
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Is it like an MSA for smart turns at a fix? That's my guess since it only applies to the turn in the one direction, perhaps they're worried about hitting something on the inside of the turn. I've never noticed that before, either.
 
COFlyBoy said:
Holy crap that was confusing.

I think I will avoid all routings that have an MTA. Finding and then decoding the MCA info on the enroutes is hard enough.
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I don't find it particularly confusing, but I'd think twice before crossing a navaid with that kind of a restriction. From the LA TAC, it looks like there's some terrain to the north-east that gets pretty high. That must be the reason - just another example of why it's a good idea to look at the VFR charts as well as the IFR charts, I guess.
 
I used to have my plane based at Brackett airfield. POM VOR is under the left downwind for RWY 26. Anyway, you bet there is high terrain to the NNW-NNE and close in. Those alts are indeed minimums for the terrain.


But I had not before heard of MTA until this thread. The link Dave provided is not confusing.
 
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It's a turn radius issue -- if, in the example above, you're making the turn from V264 eastbound to V197 northwestbound, with enough speed, you'll depart the regular protected corridor for V264 before you get into the corridor for V197. If so, they have to see if there's anything within the standard protected width of that turn radius path which will stick up higher than the MEA's and keep you above it in the turn. Put it all together, and there probably aren't many places where it's an issue, or aircraft going fast enough to have a turn radius that big, but they do have to check it and cover it if it's a problem. In any event, I don't think I'd avoid a navaid just because it has an MTA associated -- but I would be cautious about making the turn in a fast-moving plane.
 
What I find interesting about MTAs is that they don't have a speed associated with them. That is, if the intention is to make sure that aircraft making the turn really fast don't depart the protected airspace, then why don't MTAs come with an airspeed that makes the turn inside the specified radius? I would imagine that most small, light singles probably stay within the protected corridor at normal enroute speeds, but without a posted speed there's no way to determine that for sure.
 
Ron Levy said:
It's a turn radius issue -- if, in the example above, you're making the turn from V264 eastbound to V197 northwestbound, with enough speed, you'll depart the regular protected corridor for V264 before you get into the corridor for V197. If so, they have to see if there's anything within the standard protected width of that turn radius path which will stick up higher than the MEA's and keep you above it in the turn. Put it all together, and there probably aren't many places where it's an issue, or aircraft going fast enough to have a turn radius that big, but they do have to check it and cover it if it's a problem. In any event, I don't think I'd avoid a navaid just because it has an MTA associated -- but I would be cautious about making the turn in a fast-moving plane.
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How fast would I have to be going in order to depart the regular protected corridor for V264 before I get into the corridor for V197 if I make the turn IAW the FAA expectations in AIM 5-3-5.c?

c. Without such actions as leading a turn, aircraft
operating in excess of 290 knots true air speed (TAS)
can exceed the normal airway or route boundaries
depending on the amount of course change required,
wind direction and velocity, the character of the turn
fix (DME, overhead navigation aid, or intersection),
and the pilot’s technique in making a course change.
For example, a flight operating at 17,000 feet MSL
with a TAS of 400 knots, a 25 degree bank, and a
course change of more than 40 degrees would exceed
the width of the airway or route; i.e., 4 nautical miles
each side of centerline. However, in the airspace
below 18,000 feet MSL, operations in excess of
290 knots TAS are not prevalent and the provision of
additional IFR separation in all course change
situations for the occasional aircraft making a turn in
excess of 290 knots TAS creates an unacceptable
waste of airspace and imposes a penalty upon the
preponderance of traffic which operate at low speeds.
Consequently, the FAA expects pilots to lead turns
and take other actions they consider necessary during
course changes to adhere as closely as possible to the
airways or route being flown.
Click to expand...
 
jwriteclub said:
What I find interesting about MTAs is that they don't have a speed associated with them. That is, if the intention is to make sure that aircraft making the turn really fast don't depart the protected airspace, then why don't MTAs come with an airspeed that makes the turn inside the specified radius? I would imagine that most small, light singles probably stay within the protected corridor at normal enroute speeds, but without a posted speed there's no way to determine that for sure.
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This was what confused me about the link above. It makes sense that you could leave the protected area if you're going too fast, but what the heck does 10,000 feet have to do with anything? There was some statement about higher airspeeds above 10k????

I call'em strange, dang it. And I'm gonna stick to that view until I actually find one on some route I intend to fly.

Incidently, I don't recall reading about MTAs, seeing them on the enroute charts, discussing them with my CFII, or going over it on my checkride in May.
 
Is that new? I've flown over POM on the way to nearby Riverside a lot and I don't remember that restriction there as of 2009....
 
HPNPilot1200 said:
Above 10,000 feet MSL, you are not speed restricted to 250 KIAS or less (14 CFR 91.117(a))
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Gotcha, so why does the description talk about 10,000 feet instead of just saying if your IAS is greater than 250 use the MTA? Seems kinda bassakward for what they're actually trying to fix.
 
COFlyBoy said:
Gotcha, so why does the description talk about 10,000 feet instead of just saying if your IAS is greater than 250 use the MTA? Seems kinda bassakward for what they're actually trying to fix.
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What do you believe they're trying to fix?
 
roncachamp said:
That would require vectoring, affected aircraft here are on their own nav via airways.
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Then I would say it is as Ron Levy mentioned, to provide protection to high speed/large turn radius aircraft.

Actually, that was my very first thought upon reading OP's post. But I hadn't yet thought it through.
 
Richard said:
Then I would say it is as Ron Levy mentioned, to provide protection to high speed/large turn radius aircraft.
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Can you provide a scenario where that would be needed if the aircraft leads the turn as described in AIM 5-3-5.c?
 
roncachamp said:
Can you provide a scenario where that would be needed if the aircraft leads the turn as described in AIM 5-3-5.c?
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If you draw it out, you'll see that with an acute turn like the one shown, an aircraft traveling fast enough may depart the protected space on the inside of the turn (as opposed to swinging wide if the turn is started over the station). In addition, not all aircraft (and not all navaids) have the equipment necessary to accurately lead turns. Finally, the protection standards may be compromised in acute turns like this at less than 290 knots.
 
roncachamp said:
What do you believe they're trying to fix?
Click to expand...

The link in post #3 (some FAA notice date 6/30/11) describes the issue as not being able to execute the turn within the protected area of the airway.

The publication doesn't say whether the turn is before or after the navaid, though. I would expect that the worst case is when an aircraft overflies the navaid and then comes back to course. Anticipating the turn shouldn't put you very far off centerline.

My gripe with the description is that it is based on altitude instead of airspeed. Why not just say if you are going faster than X, then you need to use the MTA. I'm pretty sure I can stay within the airways even when I'm above 10k.
 
Ron Levy said:
If you draw it out, you'll see that with an acute turn like the one shown, an aircraft traveling fast enough may depart the protected space on the inside of the turn (as opposed to swinging wide if the turn is started over the station). In addition, not all aircraft (and not all navaids) have the equipment necessary to accurately lead turns. Finally, the protection standards may be compromised in acute turns like this at less than 290 knots.
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As you drew it out, how fast did the aircraft have to go in order to depart the protected space?
 
COFlyBoy said:
The link in post #3 (some FAA notice date 6/30/11) describes the issue as not being able to execute the turn within the protected area of the airway.

The publication doesn't say whether the turn is before or after the navaid, though. I would expect that the worst case is when an aircraft overflies the navaid and then comes back to course. Anticipating the turn shouldn't put you very far off centerline.
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Not explicitly, but implicitly the turn is begun at the VOR.

My gripe with the description is that it is based on altitude instead of airspeed. Why not just say if you are going faster than X, then you need to use the MTA. I'm pretty sure I can stay within the airways even when I'm above 10k.
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Let's say I'm eastbound on V264 at 10,000 MSL doing 290 KIAS. I begin the turn to V197 at COVIN, using a bank angle of 25 degrees. The turn radius would be about four miles, I'd never be east of the V197 centerline nor outside the lateral limits of the airway.

Why I'd be on that route at that altitude remains a mystery.
 
Ron Levy said:
If you draw it out, you'll see that with an acute turn like the one shown, an aircraft traveling fast enough may depart the protected space on the inside of the turn (as opposed to swinging wide if the turn is started over the station). In addition, not all aircraft (and not all navaids) have the equipment necessary to accurately lead turns. Finally, the protection standards may be compromised in acute turns like this at less than 290 knots.
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One also needs to consider that it's primarily the groundspeed that affects the turn radius over the ground as well as the required lead in.
 
gismo said:
One also needs to consider that it's primarily the groundspeed that affects the turn radius over the ground as well as the required lead in.
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Yeah -- it's fun watching my GNS530W recompute the holding pattern as GS changes during the turn.
 
Ron Levy said:
Yeah -- it's fun watching my GNS530W recompute the holding pattern as GS changes during the turn.
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My GPS is supposedly able to pre-compute the necessary tracks based on the wind data supplied by an ADC but I have yet to see this perform as advertized.
 
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