MSA Terminology Help

[keithl]

There was a thread "Use of MSA During Approach" which revealed several interpretations of MSA and various other associated matters. In my job of teaching IF Procedures I, too, have found much confusion over the various abbreviations and their detailed meaning.
So, may I appeal for anybody who has the whole story to reply, or I am going to have to do the research myself...!

Mainly from a UK perspective, but international comment also welcome, please explain the differences between MSA ('Safe' or 'Sector'?), MORA, MOCA, SSA ('Sector Safe Altitude'), JAR 'Minimum Flight Altitude', Aerad 'Contour Envelope' MSA and 'Safety Altitude' which I believe is military.

I have PANSOPS, JAROPS and UKAIP. I note that the term MSA doesn't appear in the AIP. I have the tools to do the research, but I'm a lazy man and maybe someone has already done it.

To forestall the abuse - I fully understand how we interpret and teach these things for our operation in our company. I'm after a wider perspective.

[Crossunder]

Quickly, out of the top of my head:

MSA = Minimum Sector Altitude (around a NAV aid). I know that in the States they have something called Minimum Safe Altitude, but not in Pans OPS. When cleared DTO, MSA can be used as a "ready-to-turn-on-course-altitude" if nothing is specified otherwise. Same for approaches if you're outside a STAR.

MORA = minimum off-route altitude.
Route-MORA = A sector 10NM each side of your intended track + a 10NM-radius around each end-point. Found in the AIP.
Grid-MORA: Those square grids in RFC charts with two numbers in them e.g. 46 (the "6" is superscript) means a MORA of 4.600ft in that particular "square".
Obstacle clearance varies with altitude above MSL and whether you're using Jepp or EAG etc.

MOCA = Min. Obstacle clearance alt. Company-specific for each route segment. Usually 5nm sector either side of track. Depends on navigational accuracy etc...

SSA = never heard of.

Contour envelope = probably Aerad-term. Not mentioned in EAG/Jepp RM i think.

MFA = Minimum Flight Altitude for a specified segment. Could be because of nav aid reception, airspace classifications etc.

Don't have me books 'ere, but that's it. Its all described in New Pans Ops, so just feel free to look it up ;-)

All this is basic IR stuff the students must learn. Unfortunately, I know of several CDRs(!) that are not aware of the differences between these altitudes - and their implications - and think that you can go DCT some point right away, while still on a SID, just because ATC gives you a "when ready, set course...". And who also do not care if they will be off-route when given the clearance to "go DCT X" while en-route.
I think it's great that you want to expand your knowledge!
I could also be that I'm mistaken on some or more of the above points. If so; please feel to correct me ;-)

[Zaptain]

Crossfire

MSA = Minimum Sector Altitude (around a NAV aid).

Almost.....can also be about ARP (Aerodrome Reference Point) if the relevant navaid is not located on the aerodrome. I.E. Coventry

Apart from that I would agree with all the other stuff.

I believe SSA to be transposable with MSA but just on different charts I.E. Jeppesen or Aerad.

Cheers

[keithl]

Thanks, chaps. I have done a bit of reading myself and have found that Aerad seem to be responsible for some of the confusion. SSA is Aerad pre-2000-speak for MSA (Means "Sector Safe Altitude") but is always based on ARP. Aerad also have two definitions of MSA, one means Min Sector Alt, as you have described - the other means Min Safe Alt in connection with their "MSA Contour Envelope".

Your input most useful to confirm what I think I understand from the books.

"Safety Altitude" seems to mean different things to different people, would I be right in thinking it's only for when you are lost?

[Crossunder]

Well, almost. Most of the time you're on a STAR/SID or airway, but if you are cleared "direct to" or become lost, the MSA is a good bet (if you're inside the 25nm radius of course...).
But as always, when in doubt; CLIMB!

[wellthis]

Just a couple of things to add. I don't think MOCA is company specific as it is min obstacle clearance altitude on the airway, and depending on what navaids are used in its construction, it's about 4.34 NM each side. This is not generally given by ATC rather requested by pilots in aerodromes that don't have a published approach, so one can go down have look for the RWY.

MSA (min sector altitude) is not for when you're lost since you're lost and you don't know where you are :8 , but for both starting an approach without a published transition, or for departure. It's just a safe altitude to start one off and then the rest.....

[keithl]

Thank you, one and all. I don't think I'm going to get much more, now, so...
Can I point out to all interested parties that I have found, through your responses and my own reading, at least 5 differing definitions of the abbreviation "MSA". Also, terms such as "Safety Altitude", SSA, MFA etc are in widespread use although some of them are out of date. They have their own precise meanings but are often used as if they meant the same as "MSA", whatever that actually means!
Perhaps one useful thing the JAA could do is standardise an appropriate definition.
Thanks again to those who responded.

[OzExpat]

Perhaps one useful thing the JAA could do is standardise an appropriate definition.
Thanks again to those who responded.
Or they could just adopt the ICAO abbreviations and definitions...? :}

Speaking of which, there's a new terminology that will become effective next year (and may already be in use in some countries) called the TAA, or Terminal Arrival Altitude. Essentially, this is a 25NM MSA around the IAF and IAWP - the latter terminology will disappear next year too, to be standardised on IAF.

When used with an IAF in a GNSS approach, it can have another "range ring", at some distance less than 25NM, if necessary to facilitate descent to the IAF.

MOCA is the Minimum Obstacle Clearance Altitude. It does not guarantee navaid reception. In my usual part of the world, this term is not used, the applicable terminology is LSALT - Lowest Safe ALTitude. Also in my part of the world, "Safety Altitude" is used as a generic term for AMA (Area Minimum Altitude), LSALT, MSA, LSALT and Lowest Holding Altitude. Are you sufficiently confused now? :D

[Crossunder]

I still stick to my story about the MOCA being company-specific, because it not only depends on nav aids reception, but also on the equipment carried by the aircraft. Each MOCA must be approved by the Authority. We used to fly on SAS Flight Support's plates (which show MOCA on STAR/Arrival charts etc) and had to apply to the CAA in order to use the published MOCAs. Prior to that approval we had to use the grid-MORA on the RFCs for en-route flight planning.
And as OzExpat says, on GPS-IALs you'll have three MSAs around the three IAFs (in our company it's one IAF for straight-in and two 90deg off inbound course) in addition to the "normal" MSA.

[OzExpat]

I probably shouldn't start a post with the phrase "I think", but have no choice here. I think that MOCA may have started life in the USA. I'm pretty sure that it was in use when I was flying there (late 70s/early 80s). It did not guarantee navaid reception, so there was also something called a MRA, or Minimum Reception Altitude.

If I'm anywhere near the money on this, I can hypothesize that the term migrated from the USA. This could've been because of the many pilots around the world who learned to fly (and/or did IFR training) in the USA. Therefore, the term might easily have found its way into documents issued by companies, just about any time after, say, 1979.


in our company it's one IAF for straight-in and two 90deg off inbound course) in addition to the "normal" MSA
I'm a tad hazy on the new ICAO specifications for TAAs (now into my second caraf of saki!), but I suspect that the intent is for the TAAs to replace the standard MSA. This will work well in countries that don't have a significant obstacle problem but, then, just about anything works in such places.

[keithl]

OzEx, just when I thought the topic was dead you revived it! So I hope the second carafe went down well...
JAA adopting ICAO - there's a thought. I agree, but it'll never happen, they like to put their 'mark' on everything. But it was the same under the previous setup. Most of the confusion here in UK comes from the use of "MSA" in CAP 360, which turned it into a Route, rather than a Terminal min alt. No basis in ICAO at all!
And everyone remembers it, even though it's o.o.d.
And your point about pilots training in one country and working in another is well made. We have pilots from all over, and although we (obviously) run our own training programmes, it's hard to break through their early learning.
Finally thanks for the info re: TAA. Hadn't heard of that one, yet, so I'm warned.

[OzExpat]

For some reason, the second carafe (subtle spelling correction noted with thanks :D ) always seems to go down better than the first! :ok: I didn't realise that JAR-land was trying to reinvent the wheel quite so much, so you have my sympathies.

I'm not saying that ICAO SARPS are the only way to go, but it seems ludicrous that there are 188 member countries and still no real commonality! :uhoh: :{