Grid MORA & MSA, Difference's?
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Grid MORA & MSA, Difference's?
My understanding of MORA is minimum off route altitude. Understanding it gives me 1000ft clearance for obstacles less then 5000ft and 2000ft for obstacles above 5000ft.
(This is without taking navaid use as a limitation; line of sight and all that…)
MSA, minimum safe altitude. My understanding is it gives you safe clearance within 25nm of a given reference (normally a navaid). Taking into account navaid use.
As you may have noticed, the MORA can be lower than Your MSA!
So what I would like to know how much clearance for MSA? (i'm sure it's 1000ft)
Is it fixed? And how does it take navaid use into account…?
Relation between safe altitude and navaid use please.
Excuse my ignorants....
(This is without taking navaid use as a limitation; line of sight and all that…)
MSA, minimum safe altitude. My understanding is it gives you safe clearance within 25nm of a given reference (normally a navaid). Taking into account navaid use.
As you may have noticed, the MORA can be lower than Your MSA!
So what I would like to know how much clearance for MSA? (i'm sure it's 1000ft)
Is it fixed? And how does it take navaid use into account…?
Relation between safe altitude and navaid use please.
Excuse my ignorants....
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Hi there..The MOC for MSA is 984' (fixed) within 25 nm of a navaid/fix, according to New PANS-OPS (yeah I know it's not new anymore..). But of course a thousand feet is a more conveniant number.
MORA can as you say be lower than MSA, depending on the scale of the map at hand. (If the width of a corridor square is less than 25 nm, and there is an MSA for a specific navaid covering higher terrain than the square.)
But, the MSA is always applicable regardless of navaid coverage. It is just an aid during critical phases of flight, and it is up to the pilot to determine the position in relation to the MSA-navaid/fix.
(But there might be company procedures not to "use" the MSA on the backside of a mountain (because of radio shadow) on a specific airfield,
what do I know...)
MORA can as you say be lower than MSA, depending on the scale of the map at hand. (If the width of a corridor square is less than 25 nm, and there is an MSA for a specific navaid covering higher terrain than the square.)
But, the MSA is always applicable regardless of navaid coverage. It is just an aid during critical phases of flight, and it is up to the pilot to determine the position in relation to the MSA-navaid/fix.
(But there might be company procedures not to "use" the MSA on the backside of a mountain (because of radio shadow) on a specific airfield,
what do I know...)
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I think you may find that MSA rules can vary by country. In Canada, the MSA(minimum sector altitude) guarantees 1,000 feet above the highest obstacle(weather factors considered). If cleared for an approach one can descend down to the minimum IFR altitude which will be the MSA within 25 miles of usually a navaid near the airport. The MSA is frequently but not only used in a non-radar environment. I have never encounterd a problem with navaid reception due to being at this lower altitude. I'm not sure if navaid reception at MSA is checked out by the test aircraft.
In the U.S. according to the AIM "MSA altitudes are for emergency use only and do not necessarily assure acceptable navigational signal coverage."
In the U.S. according to the AIM "MSA altitudes are for emergency use only and do not necessarily assure acceptable navigational signal coverage."
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Just to add a bit to Mike Jenvey's comment.
Correct all minimum altitudes for wind, temp and QNH when alt is set to 1013
Conditions:----------------------ADD:
Wind speed: Above 30 kts--------500' per 10 kts. Max 2000,acc to Pans-Ops
Temperature: Below standard-----4% per 10*C
QNH below 1013------------------30' per hPa
Correct all minimum altitudes for wind, temp and QNH when alt is set to 1013
Conditions:----------------------ADD:
Wind speed: Above 30 kts--------500' per 10 kts. Max 2000,acc to Pans-Ops
Temperature: Below standard-----4% per 10*C
QNH below 1013------------------30' per hPa
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Well, to answer the original question, we really need to know what sort of buffer area surrounds the grid MORA. There is a 5 NM buffer around the MSA. If this means that the MSA protection area protrudes into another grid MORA and the overall effect is that the critical obstacles are lower, then the MSA will be lower than your original grid MORA.
I think you'll find that the more accurate interpretation is a MINIMUM of 984 Feet rather than a fixed value. MSA is as susceptible to the very limited Pans Ops definition of "mountainous terrain" as a MORA or anything else.
The MOC for MSA is 984' (fixed) within 25 nm of a navaid/fix, according to New PANS-OPS (yeah I know it's not new anymore..). But of course a thousand feet is a more conveniant number.
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Perhaps I've misunderstood. Are you telling me that if I descend down to the MSA altitude 4 miles outside the charted 25 mile distance I won't come in contact with anything?
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Ozexpat wrote: "I think you'll find that the more accurate interpretation is a MINIMUM of 984 Feet rather than a fixed value. MSA is as susceptible to the very limited Pans Ops definition of "mountainous terrain" as a MORA or anything else."
Okay, to spell it out. The minimum obstacle clearance for minimum safe altitude is 984' and it is a fixed value. It cannot be higher or lower. Of course it's a MINIMUM of 984'. I just pointed out that it's a fixed minimum because the previous poster asked about it.
About the buffer..there is none(Check out ICAO Doc 8168). MSA has a 25 nm radius. MORA (grid) is within the grid. Flying outside these on min alt's you will not have required obstacle clearance.
Okay, to spell it out. The minimum obstacle clearance for minimum safe altitude is 984' and it is a fixed value. It cannot be higher or lower. Of course it's a MINIMUM of 984'. I just pointed out that it's a fixed minimum because the previous poster asked about it.
About the buffer..there is none(Check out ICAO Doc 8168). MSA has a 25 nm radius. MORA (grid) is within the grid. Flying outside these on min alt's you will not have required obstacle clearance.
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Originally Posted by RYR-738-JOCKEY
About the buffer..there is none(Check out ICAO Doc 8168). MSA has a 25 nm radius. MORA (grid) is within the grid. Flying outside these on min alt's you will not have required obstacle clearance.
Also, it has always been drummed into me that the MSA on your charts is only useable in an emergency unless you have checked the chart producers NOTAMS to ensure there have been no amendments since chart printing.
PP
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No, punkalouver, that's not what it means. It merely means that the procedure designer is making allowance for handling errors, equipment errors, etc. Otherwise, how could you be SURE that you are exactly where you think you are?
RYR-738-JOCKEY... every Pans Ops procedure has a buffer area, even for enroute flight. This fact might not be especially obvious in Volume 1 of Pans Ops - I haven't read that in too many years to be able to comment on it as its whole reason for existance is to provide basic information to people other than procedure designers. I take my guidance from Volume 2 and therefore include the requisite buffer.
RYR-738-JOCKEY... every Pans Ops procedure has a buffer area, even for enroute flight. This fact might not be especially obvious in Volume 1 of Pans Ops - I haven't read that in too many years to be able to comment on it as its whole reason for existance is to provide basic information to people other than procedure designers. I take my guidance from Volume 2 and therefore include the requisite buffer.
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"No, punkalouver, that's not what it means. It merely means that the procedure designer is making allowance for handling errors, equipment errors, etc. Otherwise, how could you be SURE that you are exactly where you think you are?"
The aircraft I fly is equipped with GPS and DME, both of which are HIGHLY accurate. THAT is how we know where we are, distance wise from a waypoint or DME station(which has slant range error however).
As for this buffer area, is this the case in all countries that have an MSA published. Perhaps it is an ICAO requirement, although countries can have differences from ICAO rules. As I noted earlier in the thread, there are differences in MSA rules just between Canada and the U.S.
The aircraft I fly is equipped with GPS and DME, both of which are HIGHLY accurate. THAT is how we know where we are, distance wise from a waypoint or DME station(which has slant range error however).
As for this buffer area, is this the case in all countries that have an MSA published. Perhaps it is an ICAO requirement, although countries can have differences from ICAO rules. As I noted earlier in the thread, there are differences in MSA rules just between Canada and the U.S.
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Yes, punkalouver, all the aeroplanes I fly are also equipped with GPS and DME and I agree that they are very accurate. However, the fundamental aspect is that a 25 MSA means 25 NM, not 29 NM or anything else. Thus, it won't matter whether any particular State has implemented MSA design differently to Pans Ops, or TERPs for that matter.
I doubt that there'd be many, if any, States that have implemented the MSA criteria any differently. The only way you could find out about that is to check the AIP for every ICAO Contracting State because there is no requirement to file a difference from any of the design criteria in Pans Ops. Differences only need to be filed in respect of Annex standards, so each State is required to state the way it has implemented Pans Ops in its AIP.
States are normally pretty cautious about loosening up design criteria because it can create a legal nightmare for them in the event of an accident or incident.
I doubt that there'd be many, if any, States that have implemented the MSA criteria any differently. The only way you could find out about that is to check the AIP for every ICAO Contracting State because there is no requirement to file a difference from any of the design criteria in Pans Ops. Differences only need to be filed in respect of Annex standards, so each State is required to state the way it has implemented Pans Ops in its AIP.
States are normally pretty cautious about loosening up design criteria because it can create a legal nightmare for them in the event of an accident or incident.
