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Raptor71
29th Apr 2015, 05:54
Hi guys,

Could you tell me how these altitudes are calculated?

I mean most of the time, MEA is higher than the MORA/MOCA.

Why provide a MORA ( Minimum Off Route Altitude) on an airway?

Why MOCA is only between VORs?

Thank you

JeroenC
29th Apr 2015, 08:35
MEA includes the abolity to receive the navaids.

Microburst2002
29th Apr 2015, 13:22
MEA is a state defined lower limit of an airway or route. It has to meet obstacle clearance, but it can be well above obstacles.

MOCA and MORAs are obstacle related and they can be (vertically) out of the airway, till the point where the minimum obstacle clearance is met.

So, you can have an airway with a MEA of FL 140 with a MORA of 3,000 ft, for instance

Goldenrivett
29th Apr 2015, 14:09
Hi Raptor71,
Could you tell me how these altitudes are calculated?
Have you tried reading some training material like:
https://ivao.aero/training/documentation/books/SPP_APC_Minimum_flight_altitude.pdf
or Page 35 onwards:
http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/instrument_procedures_handbook/media/Chapter_2.pdf

KingAir1978
30th Apr 2015, 05:58
Why provide a MORA ( Minimum Off Route Altitude) on an airway?



Sometimes you cannot follow the airway, i.e. in case of weather avoidance. If you then need to descend for a reason, it's nice to know how low one can go.

skyhighfallguy
30th Apr 2015, 06:07
Back when I was charging good money to answer questions like these (circa 1980) I was happy to answer them.

But you will appreciate things more if you actually go look up the answers yourself. Go out and buy things like the AIM, TERPS, or read the info in jeppesen manuals.

Read about such things like how designated mountainous terrain makes for different altitudes.

I'm sure you are a great person. But go do your own homework. You will thank me later.

There are some great books on instrument flying out there too. READ or go out and find a really good CFII and pay him.

Anyone answering these questions, while well meaning, is actually making it harder for new instructors or old ones to make a living.

LeadSled
30th Apr 2015, 08:37
Raptor71.
The information is all available in FAA documents on their web site for free, as they are US terms. The answers you will find there will be both comprehensive and accurate.

baobab72
4th May 2015, 20:13
Hi
MEA ensures you both reception of navaid throughout the airway and obstacle clearance 1000ft or 2000ft if over high terrain - above 5001ft -
MOCA ensures you obstacle clearance throughout the route but reception only when within 22nm from the navaid defining the route.
MORA is a jeppesen derived altitude that ensures you obstacle clearance when within the square. Why MORA? Ask yourself how often are you flying from vor to vor?

Hope it helps.


PS if i were in your shoes i would follow the hints from the previous posters: read the Jeppesen intro - there is a wealth of information in those pages!!

JammedStab
4th May 2015, 22:25
"MOCA ensures you obstacle clearance throughout the route but reception only when within 22nm from the navaid defining the route."

I have only ever seen the 22 mile thing for the American definition of MOCA. Does it apply in the EU/international as well?

Raptor71
8th May 2015, 15:17
Hi guys,

Thanks for your answer.
Do not worry I tried to look for the answers on the web or on the docs I have but it is still unclear.

I still do not get the purpose of the MORA and its name (minimum OFF ROUTE altitude)…why call it that way and associate it to an airway.
If you do not want to use the airway, there is the grid MORA.


For the MOCA, I confirm that the 22 miles are only used in the US and not in Europe! Do you think we use it in Europe just for the purpose of harmonization?

Thank you

skyhighfallguy
8th May 2015, 15:27
Minimum Off Route Altitude - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Minimum_Off_Route_Altitude)


well look here is the wikipedia on it.

and I learned something, you were talking about the route MORA and not the GRID MORA

if for some reason you don' see the link, google, MORA aviation


remember too that victor/VOR based airways have meas for the normal 4 nm/5sm from route centerline and route MORA are as described above, wider.

we have new methods of navigation in common practice now compared to the time the org altitudes were created.

So, in action to your question a ROUTE mora is 10 miles each side of an airway, GRID mora is for the whole box. Why? well, if you offset your route a little bit you can know a safe altitude. USING the whole box/GRID MORA might turn your safe altitude of 5000' to 17000' in certain parts of California for example

as for the other questions, MEA is dependent upon Navaid reception. Navaid is primarily VOR, but you could fly an airway with methods other than VOR and they are common now (gps for example), so MEA may be higher than an airway MORA in order to get LINE OF SIGHT ON VOR for nav.


At some point in your career you may want to be at the LOWEST possible SAFE altitude based on your plane's nav capability, so the lowest altitude might be lower than the MEA for obstacle clearance because your new nav doesn't have the same limitations as the VOR.
MOCA is obstacle clearance within 22nm of the VOR by definition, so you only see it with VORs. I will say it is possible for some airways to be predicated on NDB, but that is very rare now a days and then.


VORs were state of the art when original definitions were created.