MSA and Grid MORA
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MSA and Grid MORA
Just a quick Question in my previous company when Line training certain captains used to make me brief the MSA(from low level charts) to do this we would check to low level charts for the airport we were going to , I stand to be corrected but from doing a bit of research I have found that Low level charts (JEPP) use grid MORA rather than MSA , MSA is only depicted on approach plated , STAR charts and SID charts...? , so I always though that when briefing from a low-level chart I was briefing MSA not grid MORA.
Am I correct...?
Am I correct...?
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Grid MORA is the altitude at which you will clear all obstacles in the area of the grid by either 1000ft (if highest obstacle is 5000ft or less) or 2000ft (if highest obstacle is higher than 5000 ft.)
MSA are the altitudes at a radius of 25NM from a radio fix (usually the fix being used for the approach or the main fix, usually VOR, at the airport) that assure clearance of 1000 ft above all obstacles. And it is given for different sectors around the airport, hence the name.
Using Grid MORA as the minimum altitude when you are in the vicinity (i.e. within 25NM) of the aerodrome makes no sense.
1. The aerodrome may be at the intersection of 3 or 4 different grid sectors
2. The MORA may be for a point that is miles away from the airport
3. the MSA gives you a better picture (read situational awareness) of the terrain around an airport, allowing for better planning.
Take Beirut for example. To the west of the airport is the Mediterranean sea at an alt of 0 ft. To the East are mountains stretching up to 11,000 ft. You would never be able to get the whole picture simply by looking at the Grid MORA
On another note which company was this that made you brief minimum approach alts with Low Level chart Grid MORA? I would like to know so that I can stay the hell away from them. Looking at Grid MORA is a good way of getting an idea about the terrain for the extended area around the airport but not once you are in the vicinity of the field.
MSA are the altitudes at a radius of 25NM from a radio fix (usually the fix being used for the approach or the main fix, usually VOR, at the airport) that assure clearance of 1000 ft above all obstacles. And it is given for different sectors around the airport, hence the name.
Using Grid MORA as the minimum altitude when you are in the vicinity (i.e. within 25NM) of the aerodrome makes no sense.
1. The aerodrome may be at the intersection of 3 or 4 different grid sectors
2. The MORA may be for a point that is miles away from the airport
3. the MSA gives you a better picture (read situational awareness) of the terrain around an airport, allowing for better planning.
Take Beirut for example. To the west of the airport is the Mediterranean sea at an alt of 0 ft. To the East are mountains stretching up to 11,000 ft. You would never be able to get the whole picture simply by looking at the Grid MORA
On another note which company was this that made you brief minimum approach alts with Low Level chart Grid MORA? I would like to know so that I can stay the hell away from them. Looking at Grid MORA is a good way of getting an idea about the terrain for the extended area around the airport but not once you are in the vicinity of the field.
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what you didn't tell us was the purpose of the briefing...was it an approach briefing?
There are many reasons to know either grid mora or MSA...by the way, MSA can mean minimum safe altitude or minimum sector altitude.
so...what was the purpose or objective of the briefing.
by the way, the best way to know the terrain IFR is to use or at least have for reference, a vfr sectional chart or wac chart.
There are many reasons to know either grid mora or MSA...by the way, MSA can mean minimum safe altitude or minimum sector altitude.
so...what was the purpose or objective of the briefing.
by the way, the best way to know the terrain IFR is to use or at least have for reference, a vfr sectional chart or wac chart.
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Sorry, I misread the original post. I think I saw what I wanted to see there. Sorry Jack. What the above poster said is correct, which Grid MORA is technically an MSA if you mean minimum SAFE altitude. Check the Jeppesen Text --> Introduction ---> Glossary for the terms.
Airmann, your comments are spot-on. A Min Safe Altitude is exactly the same as a Min Sector Altitude: both within 25nm, and both provide 1000ft of terrain clearance, ICAO or FAA. The only diff is the M Sector Alt is used if both high bits and low bits exist.
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Minimum Safe Altitude: From what I know, and the way this terminology is used where I fly, this basically refers to an altitude whereby on route it ensures alt clearance above all obstacles for the duration of the entire flight i.e. its the highest of all MOCAs MORAs MEAs and MSAs for the entire route. So that in an emergency situation you don't have to go scanning for the specific air route or grid minimum.
Last edited by Airmann; 3rd Oct 2012 at 17:07.
