Today we are going to have a look at altitudes that will come in handy when flying, planning IFR flights and interviews (these can be asked quite a bit)
So let’s jump straight into it.
MSA (Minimum Sector Altitude)
MSA is the minimum safe altitude within a 25 nm (Nautical Mile) radius of a navigational aid. MSA will give you 1000 ft separation from the highest terrain within that sector. We normally see the MSA on our Approach plates for runways.
Can we descend below MSA? Yes, provided we are under radar control and we still remain above the radar altitudes. (Remember it is still your responsibility to make sure you don’t fly into terrain!)
MEA (Minimum En-Route Altitude)
MEA is the minimum altitude that will guarantee signal of navigation aids along the route, give you two way communication with ATC and provide obstacle clearance. MEA will give you 1000 ft separation from terrain in non mountainous areas and 2000 ft separation in mountainous areas. (Mountainous area is when a terrain change of more than 3000 ft is experienced within 10 nm)
MOCA (Minimum Obstacle Clearance Altitude)
MOCA will give you a minimum altitude above terrain and guarantee VOR reception within 22 nm from the beacon. MOCA will give you 1000 ft separation from terrain when terrain is less than 5001 ft and 2000 ft separation when terrain is more than 5000 ft.
MORA (Minimum Off-Route Altitude)
MORA will give you separation from terrain up to 10 nm off the route center line and 10 nm radius around the ends of the route. MORA will give you 1000 ft separation from terrain in non mountainous areas and 2000 ft separation in mountainous areas.
GRID MORA (Grid Minimum Off-Route Altitude)
GRID MORA gives you terrain separation within latitude and longitude lines. GRID MORA will give you 1000 ft separation from terrain when terrain is less than 5001 ft and 2000 ft separation when terrain is more than 5000 ft.
MVA (Minimum Vector Altitudes)
MVA gives you terrain separation when Vectored by ATC, remember you have to be under radar control to be able to go down to these altitudes. (often lower than the MSA) MVA will give you 1000 ft separation from terrain in non mountainous areas and 2000 ft separation in mountainous areas.
I hope these brief explanations help for interviews and make you a more knowledgeable pilot. Please comment if you have a different understanding of the above or if you would like to see any other topics.
If you would like to read more on the subject have a look at Intro to Jepp Navigation Charts
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Excellet notes
Thanks Ricardo, glad you you found them helpful!
Hi, great explanation but what about AMA (Area minimum altitude), could you elaborate on this a little bit, please? Thanks in advance.
Hi Miguel,
The AMA is the lowest off-airway altitude that can be flown under IMC that will provide a minimum vertical clearance of 1,000 feet (AGL), or in designated mountainous terrain 2,000 feet above all obstacles located in the area specified, rounded up to the nearest 100 foot increment.
Remember to always check your local laws though, they may differ.
Here is a quick link as well
https://ext.eurocontrol.int/lexicon/index.php/Area_Minimum_Altitude#Definition_Source
Hallo my dear friend. Did u mean GRID MORA? coz i didnt meet with AMA in my aviation background. Im a CPL (frozen ATPL) holder. So maybe AMA is a similar with MSA (minimum sector\safe altitude). I need more information for improoving my competishn.
This is an awesome note! Thanks!
Thanks YOLO, glad it helped!
awesome notes and illustrations , I will be going for my IFR, and your definitions helped out my understanding tremendously! Thanks
I am glad it has helped you! Good luck for your IFR test, and all the best for your future flying!
So good
Thank you!
Hi friedn what the pressure for these altitudes QNE alwaise?or some case QNH
Great and good picture
5 stars for u
Thank you!
Great!!
Could you explain MRA(Minimum Reception Altitude), too?
I will do a post in the next few weeks going over that and a few more:)
What about low temperature correction for this altitudes?
You hv explained in layman language,awsm work, thnk a lot.
Great, I am glad you enjoy it!
Simple and straightforward answers
what is MAA
Maximum Authorised Altitude is the maximum altitude you can fly without having radio interference
Awesome! thanks for adding info:)
What’s different between obstacle clearance altitude (OCA) and minimum obstacle clearance altitude?
Good day,
OCA is used in instrument approachs and MOCA is used for enroute.
Hope that helps.
Mike
Hey!
Would like to know what is the difference between AMA (Area Minimum Altitude) and GRID MORA.
Looks like the same to me!
Thanks!
They are very similar yes.
The AMA is the lowest off-airway altitude that can be flown under IMC that will provide a minimum vertical clearance of 1,000 feet (AGL), or in designated mountainous terrain 2,000 feet above all obstacles located in the area specified, rounded up to the nearest 100 foot increment.
The area is normally specified by a pair of geographic parallels and a pair of geographic meridians.
Remember to always check your local laws though, they may differ.
Here is a quick link as well
https://ext.eurocontrol.int/lexicon/index.php/Area_Minimum_Altitude#Definition_Source
I’ve seen MVA charts for terminal areas and they are a mess of random interlocking shapes and sizes denoting areas of different min altitudes. Is there any way to get these charts for specific places other than calling up TRACON for those places and asking pretty please? Also, I’ve been told to be wary of MVA and compare it to OCA/MSA for the area. I know MVA can be lower, but I was told to be careful accepting drastically lower-than-MSA altitudes in the terminal area for fear of being vectored into terrain. Thoughts?
Hi Andrew,
Generally they are available in the IFR Jeppesen bundles. But you would need to pay for these. Yes, you are correct. First of all you can only actually descend to these altitudes if you are being vectored, they technically should keep you away from terrain, but people do make mistakes. That is why it is important that you have access to the Minimum Radar Altitude chart. Perfect example was a Garuda Aircraft being vectored into a mountain just north of Medan in Indonesia. Most controllers are very competent, but I would always want to know what the actual minimums are, you are, in the end, responsible for your safety.
For the terrain clearance it will give you 1000ft above terrain (not sure of the distance from terrain) compared to the MSA which will give you 1000ft within 25nm.
Mike
Wow that was a fast response. Thank you! Where do I score Minimum Radar Altitude charts? Or what charts are they on? I’m a 99% IFR guy, so I get vectoring and controller-fu… but if it’s a sketchy mountainous area that I’m not used to on a bad weather day, sometimes you get that ol’ lovin’ feeling like you should be double/triple checking these altitudes. Like you said, people are people, and even the best make mistakes.
Hi Andrew, the easiest way would be to buy the Jepp Plates, they will keep them up to date for you. Otherwise you can always google the relevant website, ie Sacaa and search around there. It is a bit of a mission. But also if you have ForeFlight you can check it out there.
You are awesome and these are great info and illustrations. Thnx!
Thanks for the awesome comment and great feedback!
Makes it worth it.
Mike
Thank you very much