Difference between MSA and SSA
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Difference between MSA and SSA
Hi all,
Can anyone please enlighten me as to what the difference between MSA and SSA?
I cant find anything anywhere on SSA in either EU-OPs or PAN OPs.
When briefing I've always given the MSA, but apparently this is wrong, and the 25nm clearance from a fix is actually called the Sector Safe Altitude.
Thanks in advance.
Can anyone please enlighten me as to what the difference between MSA and SSA?
I cant find anything anywhere on SSA in either EU-OPs or PAN OPs.
When briefing I've always given the MSA, but apparently this is wrong, and the 25nm clearance from a fix is actually called the Sector Safe Altitude.
Thanks in advance.
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No; you are right. The 25nm* of 1000-ft-clearence above obstacles is called the MSA - Minimum Sector Altitude (ref PANS-OPS Vol II, Chapter 8 MSA).
*) Obstacles within a buffer zone of 9 km (5 NM) around the boundaries of any given sector shall be considered as well. (Verbatum from the above ref.)
What have you been told?
During my pilot training (in the US) I was told... "If there is one sector, it is called Minimum Safe Altitude. If there are more than one sector, it is called min sector altitude". Never heared about SSA (or is that a British thing?
)
*) Obstacles within a buffer zone of 9 km (5 NM) around the boundaries of any given sector shall be considered as well. (Verbatum from the above ref.)
What have you been told?
During my pilot training (in the US) I was told... "If there is one sector, it is called Minimum Safe Altitude. If there are more than one sector, it is called min sector altitude". Never heared about SSA (or is that a British thing?
)
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MSA can mean "Min Safe Alt" or "Min Sector Alt" and unfortunately, dont mean the same thing.
The Min Safe Alt version relates to the 25nm circle, with ROC additives 1000/2000 depending.
Min Sector Alt is usually a subset of the Min Safe Altitude. These are frequently noted on the charts with the individual sectors/arcs noting different minimums per sector, rather than the overall Min Safe Altitude...which may be far too restrictive for operations.
In regards to SSA, I have not heard of that...but well....
The Min Safe Alt version relates to the 25nm circle, with ROC additives 1000/2000 depending.
Min Sector Alt is usually a subset of the Min Safe Altitude. These are frequently noted on the charts with the individual sectors/arcs noting different minimums per sector, rather than the overall Min Safe Altitude...which may be far too restrictive for operations.
In regards to SSA, I have not heard of that...but well....
Last edited by FlightPathOBN; 19th Apr 2011 at 19:40.
Use it to avoid ramming the scenery.
I can't imaging a sensible, useful approach briefing which neglected sector safe altitudes. Piece of wee-wee at a coastal airport with no nearby hills, but rather different at some mountainous airport surrounds.
I can't imaging a sensible, useful approach briefing which neglected sector safe altitudes. Piece of wee-wee at a coastal airport with no nearby hills, but rather different at some mountainous airport surrounds.
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Huh? Why? Don't you almost always descend below the MSA while on radar vectors? Min vectoring altitude(MVA) is, after all, usually lower than MSA. Do you refuse a vector below MSA? If so, good luck ever getting vectored below an overcast layer and then being cleared for a visual approah. You'll be costing your company a lot of fuel...
So again. Why are you briefing MSA?
As far as I can tell, it is only useful in cases of lost comm while on a vector. That's about a 1/1,000,000 type thing. And when it happens, there's no way in hell you will have remembered from the brief 20 minutes ago that the NE quadrant MSA was 5200'.
There may be a good reason for briefing it. I just haven't heard it yet.
So again. Why are you briefing MSA?
As far as I can tell, it is only useful in cases of lost comm while on a vector. That's about a 1/1,000,000 type thing. And when it happens, there's no way in hell you will have remembered from the brief 20 minutes ago that the NE quadrant MSA was 5200'.
There may be a good reason for briefing it. I just haven't heard it yet.
Reasons to brief msa....CFIT, airmanship, self preservation etc etc
Reasons not to...it's an unlikely event (jriv's words not mine). Oh well I'll stop briefing emergencies then using that logic - not!
Reasons not to...it's an unlikely event (jriv's words not mine). Oh well I'll stop briefing emergencies then using that logic - not!
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The whole MSA thing is a bit of a dogs dinner. Depending on where you look, there are numerous different 'definitions' and acronyms. Colloquially, pilots, companies and regulators use the term for safety altitudes that have nothing to do with the 25nm (PANS-Ops described) approach scenario.
Firstly, the FAA (FAR 91.119) describes 'minimum safe altitude' which loosely correlates to the UK Rule 5/6 (ie not scaring the public with low flying).
Folklore also has a part to play and we have people banding around the term MSA with regards to en-route (ie not the approach or departure phase) of flight. This argument is fuelled by companies such as Garmin shoving a software derived MSA on their GPS; in their case the figure appears to be derived from an MEF grid with an additional 10nm buffer. Why you would want such a broadly calculated altitude depicted on a piece of equipment that tells you exactly where you are, within a matter of feet, is beyond me
. Alternatively, third party navigation software providers have a different interpretation of MSA. For example, SkyDemon (a VFR flight planning application) indicates:
When challenged as to how they have decided upon these criteria their response is that they have responded to customer feedback.
Equally, some counties (UK for example) have IFR that talk about safety altitude (Rule 33) which is the 1000ft/5nm scenario.
I suppose much of the argument comes down to whether a pilot knows where he is, or isn't. Personally, I shiver at the loose use of terminology which, in reality, is rather important. To me, MSA is to do with the approach phase of flight which can be refined to SSAs and, if available, MVAs (RMACs) .
Confused?
Firstly, the FAA (FAR 91.119) describes 'minimum safe altitude' which loosely correlates to the UK Rule 5/6 (ie not scaring the public with low flying).
Folklore also has a part to play and we have people banding around the term MSA with regards to en-route (ie not the approach or departure phase) of flight. This argument is fuelled by companies such as Garmin shoving a software derived MSA on their GPS; in their case the figure appears to be derived from an MEF grid with an additional 10nm buffer. Why you would want such a broadly calculated altitude depicted on a piece of equipment that tells you exactly where you are, within a matter of feet, is beyond me
. Alternatively, third party navigation software providers have a different interpretation of MSA. For example, SkyDemon (a VFR flight planning application) indicates:
The MSA for a leg is calculated by looking at the terrain and obstructions 4nm either side of the leg, with 1000ft clearance for obstructions and 800ft clearance for terrain.
Equally, some counties (UK for example) have IFR that talk about safety altitude (Rule 33) which is the 1000ft/5nm scenario.
I suppose much of the argument comes down to whether a pilot knows where he is, or isn't. Personally, I shiver at the loose use of terminology which, in reality, is rather important. To me, MSA is to do with the approach phase of flight which can be refined to SSAs and, if available, MVAs (RMACs) .
Confused?
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I don't think jriv is serious!? Also he/she demonstrates a short memory span (20 minutes?) for important stuff and, as mustafagander and BBK say, appears not to be concerned about SA!
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I'm actually quite serious.
Are you really refusing a lower altitude while on a vector?
If I lose comm while on a vector, the MSA is the first thing I will check. There is no way I am just going to start climbing without checking the chart (a 2 second procedure), as some MSAs are broken into several sectors, all with different altitudes - a very easy thing to mix up.
As for SA, I agree it is important to know where the high terrain is, but I have never heard anybody refuse a lower altitude because it was below MSA.
I understand what you guys are saying, and if the other pilot I am flying with wants to brief it, so be it. I really don't care. I'm just trying to understand what I'm missing.
Are you really refusing a lower altitude while on a vector?
If I lose comm while on a vector, the MSA is the first thing I will check. There is no way I am just going to start climbing without checking the chart (a 2 second procedure), as some MSAs are broken into several sectors, all with different altitudes - a very easy thing to mix up.
As for SA, I agree it is important to know where the high terrain is, but I have never heard anybody refuse a lower altitude because it was below MSA.
I understand what you guys are saying, and if the other pilot I am flying with wants to brief it, so be it. I really don't care. I'm just trying to understand what I'm missing.
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Software derived MSA is not a good idea. There are additives for mountainousness terrain, precipitous terrain, and other issues to take into account.
Some regulators adjust the MSA with airspace separation in mind as well.
With the MVA, you are on approach clearances, and they could be below the MSA as now you are dealing with different ROC parameters and separation issues. This also allows for ATC do give you a direct with a go-around, rather than going back to the STAR
Some regulators adjust the MSA with airspace separation in mind as well.
With the MVA, you are on approach clearances, and they could be below the MSA as now you are dealing with different ROC parameters and separation issues. This also allows for ATC do give you a direct with a go-around, rather than going back to the STAR
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Originally Posted by jriv
Are you really refusing a lower altitude while on a vector
Also, by briefing it (within memory span...) if comms are lost I do not need to grab for a map to establish MSA nor during a GPS pull up do I need to do that. Are you telling me that in a GPS pull up' you and/or the other crew members are going to be grabbing a map?
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The MSA is on the approach chart which is sitting right in front of me. There is no digging required.
As for a GPWS pullup: that has nothing to do with MSA. Why on earth would anybody look at a chart when the system is telling you to "pull up or die?"
I'm not trying to upset anybody here. No need for the silly hypotheticals.
As for a GPWS pullup: that has nothing to do with MSA. Why on earth would anybody look at a chart when the system is telling you to "pull up or die?"
I'm not trying to upset anybody here. No need for the silly hypotheticals.
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JRIV,
For what it's worth, we brief MSA why:
1) Situational awareness, in case of Emergency descent, or Engine Out Cruise or Loss of ATC when under vectors, the list goes on, comes under the general heading " Airmanship"
2) Ops manual specify max rate of descent within xx feet of MSA, for instance 3000 fpm within 3000 feet of the MSA, 2000, within 2000, 1000 within 1000 etc.
3) If we descend in VNAV, which is normal, with a tailwind or late descent cleared we may well be over the allowed ROD for the sector and rsik the hard warnings.
4) Even under radar vectors PM must state " below MSA" we have to know this for many reasons, windshear go-arounds, RA,s etc navigation with loss of FMS etc, ( this is not a clue for the raw data brigade to get on high horses)
In many parts of the world where there is a non-radar environment, Turkey for instance, you will not be cleared to a level below MSA until XXX DME and the controller know where you say you are. In this position the descent planning in the geometric path VNAV can be useless and again, " airmanship" comes into play.
For what it's worth, we brief MSA why:
1) Situational awareness, in case of Emergency descent, or Engine Out Cruise or Loss of ATC when under vectors, the list goes on, comes under the general heading " Airmanship"
2) Ops manual specify max rate of descent within xx feet of MSA, for instance 3000 fpm within 3000 feet of the MSA, 2000, within 2000, 1000 within 1000 etc.
3) If we descend in VNAV, which is normal, with a tailwind or late descent cleared we may well be over the allowed ROD for the sector and rsik the hard warnings.
4) Even under radar vectors PM must state " below MSA" we have to know this for many reasons, windshear go-arounds, RA,s etc navigation with loss of FMS etc, ( this is not a clue for the raw data brigade to get on high horses)
In many parts of the world where there is a non-radar environment, Turkey for instance, you will not be cleared to a level below MSA until XXX DME and the controller know where you say you are. In this position the descent planning in the geometric path VNAV can be useless and again, " airmanship" comes into play.