RNAV (no TAA) - Cleared for the approach. When to descend?

As an extreme example of my last post, Santa Fe, NM, SAF, RNAV (GPS) RWY 2, has an MSA of 13,800 due to the mountains to the NE 20+ nm away. But coming from the southwest, all of the Initial segments leading to the IF have minimum altitudes of "just" 10,000. Presumably this would be a safe altitude for Center to send you direct to WODES (IF) from just about anywhere to the southwest. If you want to stay at 13,800 until WODES, you'd have a heck of a descent to make before the FAF at 7800!

 
RussR said:
...Let's say the MSA is 4300 and ATC says "Maintain 3500 until XXXXX, cleared approach". You check the MSA and verify that it is indeed 4300. What do you intend to do in this case? The correct answer is to descend to 3500 as cleared....
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Sorry again. To be clear, I'm talking about _practice_ approaches without ATC. It would take a lot for me to question ATC altitude direction.
 
MauleSkinner said:
Looking at MSA in deciding whether or how to accept an ATC clearance can definitely steer you in the wrong direction.
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Sorry @MauleSkinner, I tried to make it clear the distinction between practice approaches and ATC. I would not question ATC based on published MSA.
 
Mahneuvers said:
Sorry. I didn't mean to take the thread in a different direction. When starting practice approaches, a CFII taught me to first make sure I'm at or above the MSA. To me, it's akin to "maintain X until..." if talking to ATC. Frankly, I only chimed in to poke some fun a eman :)
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Sounds like some clarification of MSA is necessary. It is like OROCA. It gives you a general idea of the terrain around you. If you are on a published route, then MSA is not relevant.
 
RussR said:
That CFII taught you something that is not a correct application of the MSA, and through no fault of your own you are now forever going to apply it incorrectly. It's called "primacy" and it's hard to break.

The MSA is in no way a procedural altitude. It has no bearing on how high or low you need to fly on an approach. ATC minimum altitudes can be, and often are, lower than MSA.

Let's say the MSA is 4300 and ATC says "Maintain 3500 until XXXXX, cleared approach". You check the MSA and verify that it is indeed 4300. What do you intend to do in this case? The correct answer is to descend to 3500 as cleared.

MSAs are established by drawing a 25nm + 4 nm buffer = 29 nm circle around the MSA fix, and finding the tallest obstacle in that circle, and adding 1000 ft. (VOR-based MSAs can be sectorized to get lower altitudes, but RNAV ones cannot.) That means that the obstacle controlling that MSA altitude could be literally 50 nm away from your location, and nowhere near your route to get to the first procedural fix.
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Yea, apply that rule to this airport: https://aeronav.faa.gov/d-tpp/2308/00606R9.PDF

It could make that descent to final a bit dicey.
 
sarangan said:
Sounds like some clarification of MSA is necessary. It is like OROCA. It gives you a general idea of the terrain around you. If you are on a published route, then MSA is not relevant.
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Even if you're not on a published route. ATC has their own MVAs which are frequently less than the MSA. If you're on a published route you use the published altitude.
 
sarangan said:
What kind of emergencies are we talking about?
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That's up to the pilot-in-command. For me, it would be any situation in which I didn't have enough information to guarantee terrain and obstruction clearance.

Sorry, I can't be more specific, because I've never been in a situation in which using the MSA was necessary.
 
Mahneuvers said:
I'll let him know. Not sure how this invalidates his advice.
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What advantage is there in being at an altitude that could make an excessive descent rate necessary? Sounds like the opposite of a stabilized approach.

Not being in contact with ATC would make it worse, because starting an approach from an unusually high altitude could take them by surprise, creating a potential for traffic conflicts.

By the way, you might want to show him the definition of "minimum safe altitude (MSA)" in the FAA's Pilot/Controller Glossary. It specifically states that when an MSA is published on an approach chart, it's for emergency use only. So it's not just me saying it.
 
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Mahneuvers said:
Sorry again. To be clear, I'm talking about _practice_ approaches without ATC. It would take a lot for me to question ATC altitude direction.
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There's nothing to be sorry about. you're just repeating something that was passed on to you.

but think... what do practice approaches without ATC have to do with it? If you are flying a practice approach, aren't you (1) flying an area you are familiar with, (2) flying the altitudes specified by the procedure, (3) remaining in the area of the approach chart where the obstructions are charted, and (4) using a safety pilot to avoid obstructions?

Did you look to see what your CFII's rule would mean at Santa Fe?Are you by chance in an area very unlike Santa Fe? Relatively flat where the MSA is only a couple of hundred feet higher than procedural altitudes?
 
sarangan said:
What kind of emergencies are we talking about?
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Ultimately it's a PIC decision when it's needed. Not much help in a power failure! I suspect originally it was mostly about loss of nav capability in an era when charted Information was limited.

That's probably where I would expect to use it - loss of both nav and of enough situational awareness to not know more than that I'm about 25 miles from the MSA center.
 
midlifeflyer said:
Ultimately it's a PIC decision when it's needed. Not much help in a power failure! I suspect originally it was mostly about loss of nav capability in an era when charted Information was limited.

That's probably where I would expect to use it - loss of both nav and of enough situational awareness to not know more than that I'm about 25 miles from the MSA center.
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The pilot controller glossary says "MSAs are for emergency use only and do not necessarily assure acceptable navigational signal coverage." My take is that MSA is similar to MOCA and OROCA, but the phrase 'emergency' never made much sense to me in this context.
 
sarangan said:
The pilot controller glossary says "MSAs are for emergency use only and do not necessarily assure acceptable navigational signal coverage." My take is that MSA is similar to MOCA and OROCA, but the phrase 'emergency' never made much sense to me in this context.
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I read "signal coverage" to mean ground-based navaids. The whole concept probably means less that it used to. There's a lot of that in the IFR world,
 
From the IFR Procedures Handbook: "Minimum Safe/Sector Altitude Minimum Safe Altitudes are published for emergency use on IAP charts. MSAs provide 1,000 feet of clearance over all obstacles but do not necessarily assure acceptable navigation signal coverage. The MSA depiction on the plan view of an approach chart contains the identifier of the center point of the MSA, the applicable radius of the MSA, a depiction of the sector(s), and the minimum altitudes above mean sea level which provide obstacle clearance. For conventional navigation systems, the MSA is normally based on the primary omnidirectional facility on which the IAP is predicated, but may be based on the airport reference point (ARP) if no suitable facility is available. For RNAV approaches, the MSA is based on an RNAV waypoint. MSAs normally have a 25 NM radius; however, for conventional navigation systems, this radius may be expanded to 30 NM if necessary to encompass the airport landing surfaces. Depicted on the Plan View of approach charts, a single sector altitude is normally established. However, when it is necessary to obtain obstacle clearance, an MSA area may be further divided with up to four sectors."

FYI the AIM has the exact same verbiage on MSAs.

:deadhorse:
 
midlifeflyer said:
that's the second time MSA has been mentioned. What's the emergency? I haven't seen mention of lost com or nav capability, electrical failures, or some of the other things that would make the MSA relevant in the US. Just a simple everyday instruction to maintain an assigned altitude until on a published course.

Lest we forget...

MSA means minimum safe altitude, expressed in feet above mean sea level, depicted on an approach chart that provides at least 1,000 feet of obstacle clearance for emergency use within a certain distance from the specified navigation facility or fix.
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Because once cleared for the approach, within the 25 miles, you can descend to that altitude, unless your clearance says, like this one, "maintain XXX until...."
 
MauleSkinner said:
Got a reference for that?
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www.aviationsafetymagazine.com

Cleared For The MSA? - Aviation Safety

Not long ago, I was conducting a two-day, six-flight, expanded instrument proficiency check (IPC) with the owner of an A36 Bonanza. We were above an undercast at 7000 feet en route from Wichita, Kans., to Emporia Municipal (EMP), a non-towered airport a short 25 minutes to the northeast. Had the...
www.aviationsafetymagazine.com www.aviationsafetymagazine.com
 
Pinecone said:
www.aviationsafetymagazine.com

Cleared For The MSA? - Aviation Safety

Not long ago, I was conducting a two-day, six-flight, expanded instrument proficiency check (IPC) with the owner of an A36 Bonanza. We were above an undercast at 7000 feet en route from Wichita, Kans., to Emporia Municipal (EMP), a non-towered airport a short 25 minutes to the northeast. Had the...
www.aviationsafetymagazine.com www.aviationsafetymagazine.com
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One would think Aviation Safety magazine would know the difference between an MSA and a TAA.
 
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midlifeflyer said:
It's actually shocking considering who wrote it. I can't even agree with the premise.
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Btw, see @John Collins comment to the article. Spot on.

Point is, they *were* on a published segment. Beware of confusing:

MSA - "minimum safe altitude". A non-operational altitude for emergency use.
TAA - terminal arrival area. A charted ("published") segment of an approach procedure.

AIM: "Maintain the last altitude assigned by ATC until the aircraft is established on a published segment of a transition route, or approach procedure segment, or other published route, for which a lower altitude is published on the chart. If already on an established route, or approach or arrival segment, you may descend to whatever minimum altitude is listed for that route or segment."

A TAA qualifies. An MSA does not.
 
RussR said:
That CFII taught you something that is not a correct application of the MSA, and through no fault of your own you are now forever going to apply it incorrectly. It's called "primacy" and it's hard to break.

The MSA is in no way a procedural altitude. It has no bearing on how high or low you need to fly on an approach. ATC minimum altitudes can be, and often are, lower than MSA.

Let's say the MSA is 4300 and ATC says "Maintain 3500 until XXXXX, cleared approach". You check the MSA and verify that it is indeed 4300. What do you intend to do in this case? The correct answer is to descend to 3500 as cleared.

MSAs are established by drawing a 25nm + 4 nm buffer = 29 nm circle around the MSA fix, and finding the tallest obstacle in that circle, and adding 1000 ft. (VOR-based MSAs can be sectorized to get lower altitudes, but RNAV ones cannot.) That means that the obstacle controlling that MSA altitude could be literally 50 nm away from your location, and nowhere near your route to get to the first procedural fix.
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Do you know what the rationale is behind “…VOR-based MSAs can be sectorized to get lower altitudes, but RNAV ones cannot…” It makes no sense to me.
 
luvflyin said:
Do you know what the rationale is behind “…VOR-based MSAs can be sectorized to get lower altitudes, but RNAV ones cannot…” It makes no sense to me.
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No I do not. It's always been that way as far as I know.
 
As luvflyin' implied, these "what would you do" scenarios are made so much harder when pilots use vague/sloppy phraseology. Assuming you were on a random route at the time, ATC would need to provide an altitude to maintain until established on a published route or segment of the approach. In the case of being re-routed direct to the IAF, that would constitute a random route, so ATC would need to include an altitude to maintain until the requirement was met. This would be done with a "cross [IAF name] at or above [MIA/MVA], cleared [approach name]."

There isn't really a productive discussion to be had about when you can start down....it's not subjective or update for debate. You'd cross the IAF at or above the ATC-specified altitude, after which you could descend to the altitudes associated with the various segments of the approach.

A lot of the confusion here is because of the '...until established' verbiage. My guess is this was a pilot recollection error (this happens daily in the environment in which I work where pilots recall instructions, mangling the phraseology into something that is markedly different from what was actually issued), OR the controller made an uncharacteristic error. The only time 'established' would be used in the altitude restriction, typically, is during a vector to the final approach course, or if the controller specifically says, "until established on a segment of the approach," (have heard that one IRL a couple of times, but it's rare as the 'cross' instruction handles it just fine when you're being sent to an IAF or IF).
 
coma24 said:
As luvflyin' implied, these "what would you do" scenarios are made so much harder when pilots use vague/sloppy phraseology. Assuming you were on a random route at the time, ATC would need to provide an altitude to maintain until established on a published route or segment of the approach. In the case of being re-routed direct to the IAF, that would constitute a random route, so ATC would need to include an altitude to maintain until the requirement was met. This would be done with a "cross [IAF name] at or above [MIA/MVA], cleared [approach name]."

There isn't really a productive discussion to be had about when you can start down....it's not subjective or update for debate. You'd cross the IAF at or above the ATC-specified altitude, after which you could descend to the altitudes associated with the various segments of the approach.

A lot of the confusion here is because of the '...until established' verbiage. My guess is this was a pilot recollection error (this happens daily in the environment in which I work where pilots recall instructions, mangling the phraseology into something that is markedly different from what was actually issued), OR the controller made an uncharacteristic error. The only time 'established' would be used in the altitude restriction, typically, is during a vector to the final approach course, or if the controller specifically says, "until established on a segment of the approach," (have heard that one IRL a couple of times, but it's rare as the 'cross' instruction handles it just fine when you're being sent to an IAF or IF).
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Yeah, pilots don't always always recall the exact verbiage the controller used when describing scenarios in these forums. And it leads to confusion often. And I think controllers making errors may be a little more often than as you said "...an uncharacteristic error..." The until established thing I hear a lot. The rule is...

b. For aircraft operating on unpublished routes, issue the approach clearance only after the aircraft is:
1. Established on a segment of a published route or instrument approach procedure, or 2. Assigned an altitude to maintain until the aircraft is established on a segment of a published route or instrument approach procedure.

But there is no prescribed phraseology that says "...established on a segment..." and none that end with just 'until established.' What is being established on must be named. You gave an example above with "...cross [IAF name] at or above [MIA/MVA], cleared [approach name]." Very common is the localizer ", “Four miles from LIMA. Turn right heading three four zero. Maintain two thousand until established on the localizer. Here's for TAA's, "...Cleared direct CHARR, maintain at or above five thousand until entering the TAA, cleared RNAV Runway One−Eight Approach.”

To many controllers seem to read the rule, "... Assigned an altitude to maintain until the aircraft is established on a segment of a published route or instrument approach procedure...", turn it int an ad hoc phraseology and leave it at that and just say established with out naming established on what.


 
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I think it is largely historical. The MSA is centered not on the airport often, but some convenient VOR and a single number.
TAAs on the other hand were sectorized for operational reasons but someone say "Why can't we just use that for what the MSA emergency alt."
 
flyingron said:
I think it is largely historical. The MSA is centered not on the airport often, but some convenient VOR and a single number.
TAAs on the other hand were sectorized for operational reasons but someone say "Why can't we just use that for what the MSA emergency alt."
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Here’s some history. https://www.faa.gov/sites/faa.gov/files/2022-07/Hist_22-01-368.pdf
It makes sense to not sectorize conventional nav MSA’s centered on the airport. The airport has no radials to identify the sectors so one altitude makes sense. What doesn’t make sense to me is that RNAV MSA’s are not sectorized. What could easier to do than determine your direction from a Waypoint than using a GPS Navigator. As far as why can’t we use the TAA’s, feel free to do it. MSA’s are emergency altitudes. In an emergency you have the authority to make the decision.
 
luvflyin said:
Here’s some history. https://www.faa.gov/sites/faa.gov/files/2022-07/Hist_22-01-368.pdf
It makes sense to not sectorize conventional nav MSA’s centered on the airport. The airport has no radials to identify the sectors so one altitude makes sense. What doesn’t make sense to me is that RNAV MSA’s are not sectorized. What could easier to do than determine your direction from a Waypoint than using a GPS Navigator. As far as why can’t we use the TAA’s, feel free to do it. MSA’s are emergency altitudes. In an emergency you have the authority to make the decision.
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I'm thinking in the opposite direction. Why have any sectorized?

At least part of the underlying assumption is that the emergency is a loss of navigational capability. If you only have a vague idea where you are, might as well just use your sectional chart or LIFR chart OROCAs.
 
luvflyin said:
Here’s some history. https://www.faa.gov/sites/faa.gov/files/2022-07/Hist_22-01-368.pdf
It makes sense to not sectorize conventional nav MSA’s centered on the airport. The airport has no radials to identify the sectors so one altitude makes sense. What doesn’t make sense to me is that RNAV MSA’s are not sectorized. What could easier to do than determine your direction from a Waypoint than using a GPS Navigator. As far as why can’t we use the TAA’s, feel free to do it. MSA’s are emergency altitudes. In an emergency you have the authority to make the decision.
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midlifeflyer said:
I'm thinking in the opposite direction. Why have any sectorized?

At least part of the underlying assumption is that the emergency is a loss of navigational capability. If you only have a vague idea where you are, might as well just use your sectional chart or LIFR chart OROCAs.
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These two posts kind of highlight the "plot hole" that is the MSA.

What is the MSA? I've always been taught and thought of it as "if you have an emergency, you can climb to to this altitude within this area and not safely fly around randomly while figuring out your problem and not hit anything." But even from the first look this is flawed. For example, I learned to fly instruments in planes without even DME. So how would I comply with the "within 25 nm" rule? My intention was always that since I was in a 172 or similar, if I just stayed somewhere near the VOR I'd certainly not stray too far.

But realistically, if I have enough NAV capability to determine that, I can probably fly an approach. Or I could at least enter a holding pattern to work out my gear issue or whatever it is. But of course, if I have Comm, I'll be asking ATC for help anyway, and they can direct me somewhere safe at a safe altitude.

The author of the PDF linked above (Garmin employee) also seems to be unclear on the purpose of the MSA. He writes several times about the MSA coverage not being sufficient to "get you to" the respective approach procedure. But that's not the intent of an MSA (of course, the "intent" is probably no longer really applicable anyway and could probably do to be changed).

Also, the whole reason that an RNAV MSA is based on the MAP is simple - that fix is already in your route if you have the approach loaded. If you fly the approach and do nothing once going missed, it stays in there, and the distance to it is readily displayed. What could be easier? If it was changed to the ARP, you'd have button-dialing to do during an otherwise busy time.

The non-RNAV based MSA issue is a tricky one, and yes, needs to be revised. The number of "omni-directional facilities" keeps shrinking, and so finding one close to an ILS is sometimes not even possible. But one of the basic tenets of TERPS is to try to provide for the least-equipped airplane, i.e. VOR-only. But that's becoming less and less realistic and less practical, and more restrictive as time goes on. Perhaps it's time to change that philosophy.

I'd be interested to know from the folks here - have you ever actually "used" an MSA for its intended purpose? Know anybody who has? How recently? I've been flying for over 30 years and have never once needed to use an MSA due to some emergency/partial navigational failure. Maybe I'm just lucky, but I imagine my experience is typical.
 
flyingron said:
TAAs on the other hand were sectorized for operational reasons but someone say "Why can't we just use that for what the MSA emergency alt."
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You can and should. You will note that on RNAV procedures with a TAA, there is no MSA depicted. The TAA is to be used in lieu of the MSA if needed.
 
RussR said:
You can and should. You will note that on RNAV procedures with a TAA, there is no MSA depicted. The TAA is to be used in lieu of the MSA if needed.
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You misunderstood me... I was speaking as the TERPS guys who designed how the plates were going to be designed.
 
midlifeflyer said:
I'm thinking in the opposite direction. Why have any sectorized?

At least part of the underlying assumption is that the emergency is a loss of navigational capability. If you only have a vague idea where you are, might as well just use your sectional chart or LIFR chart OROCAs.
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I dunno. Seems if you're going to have one, at least have it make sense. Example, the RNAV(GPS) Approaches at KEYE. OROCA no help there, it's 15,200 and you'd probably run into the same syndrome with other airports with ridiculously high unsectorized MSA's
 
Having flown a lot of TAAs, not sure why the author was unfamiliar with the sectorized presentation of the safe altitudes in each sector. Since often fly in fairly rugged semi-mountainous terrain, on a new approach will check the sector altitude to insure Center hasn't given me too low an altitude - i.e., "they've descended us to 5100', were are cleared for the approach, and were are 24 miles away in a sector where the minimum safe altitude is 4500'." All good. No need to actually descend to the minimum until on a feeder "T" then hold that altitude until GS intercept. Unless you like to reconfigure and drop down to a lower altitude.
 
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