25 mile MSAs & the 10 mile MSAs within...

[Dr Reedalldabooks]

Hi all,

I was just wondering if anyone could shed any light on the point of having the 10NM MSA height higher than its 25NM MSA. I know this sounds confusing but I will give you an example. In NADI, the MSA is 3400’ in the northwestern quadrant, 3100’ in the southwestern quadrant and 4700’ in the southeastern quadrant. However, underneath it says 5100’ within 10NM. (the northeastern quadrant is 5300’).

My question is: what is the point of this and is it a safety issue to have an MSA jump 2000’ like in the southwestern quadrant when coming within 10 miles. I understand that somewhere like Nadi which it is based on the Eastern coast that you think you won’t won’t hit anything at 3100’ but that’s not my point, legally to stay about the MSA you would have to be at 5100’ within 10NM. I would have thought in an airport such as this that if 5100’ is the highest MSA (within 10NM) than make all the MSAs lower than 5100’ to 5100’, or do what is done in an airport such as Mumbai where is specifies that the eastern MSA drops from 3900’ to 2600’ within 12 miles whist the western MSA remains at 3100’. i.e. it specifies which section of the MSA is to change. For example if the point of having 5100’ within 10NM in Nadi is to allow the people coming from the northeastern quadrant to descend from 5300’ to 5100’ within 10NM then specify that the 5100’ within 10NM applies to the section only, as they do in other places (Mumbai, Milan, Cologne-Bonn are a few I have come across) so that the people coming from the other quadrants (in the case of Nadi) can remain at the lower heights of 3400’, 3100’ or 4700’.

Is there a case for other operators where at night or in IMC they need to get down to a lower altitude after 10NM and is this why these lower MSAs outside 10NM exist? I cannot think why this would be, so I think it would be safer that if they are unable to specify each quadrant that the 5100’ apples to due to the geography of the land, then shouldn’t they just make the 3100’, 3400’ and 4700’ MSAs all 5100’ to avoid a situation where someone misreads the chart and misses the 5100’ within 10NM and ends up flying in one case 2000’ below the MSA when they come in at 3100’ within 10NM.

If I am missing a point or a rule here than please let me know. But if in fact the geography of the land was able to specify a quadrant(s) that the 5100’ related to then it would seem to make more sense to have apply this so when east of the coast for instance, instead of restricting yourself to 5100’ when landing on rwy 02 from the southwest would be possible to descend to 3100’ all the way in as long as you remained west of the 180 radial.

Nadi is not the only airport this happens at. Adelaide the MSA in the west goes from 1800’ within 25NM to 3800’ within 10NM. Brisbane goes from 2100’ within 25NM in the east to 2500’ within 10NM. Cairns from 5200’ in the northwest and 4000’ in the northeast within 25NM to 5600’ within 10NM. Learmonth goes from 1900’ in the east within 25NM to 2300’ within 10NM. These are just the few I have come across so far. I understand most of these airports have radar, however not all of them do and it isn’t always working (or manned). Further to this there are airports where the 10NM MSA is lower than the 25NM. For example Avalon drops from 3700’ and 2700’ within 25NM to 2500’ within 10NM, Chennai 2300’ within 25NM to 1800’ within 10NM, Tindal 2300’ within 25NM to 2200’ within 10NM and Melbourne 4500’ and 3700’ within 25NM down to 3300’ within 10NM. These changes make sense as they are going from higher to lower MSA’s rather than the other lower to higher ones I have illustrated above.

It think there is a safety issue here and that if a higher section of MSA for lowering cannot be specified for geographical reasons and therefore sections of the 25NM MSA rise when within 10NM MSA, then why not make the whole of an MSA section within 25NM that is lower than the MSA within 10NM equal to 10NM MSA. As the MSA is only going to be legally used during night ops or IMC then I believe doing this will eliminate a possible error and confusion. For example, if in Nadi is is not possible to actually specify a section of the MSA that goes to 5100’ and it all does, then make the 25NM quadrants of 3100’, 3400’ and 4700’ all 5100’ as within 10NM they all rise to 5100’ anyhow. Further, if it was geographically possible for a specific 25NM MSA sector higher than the 10NM MSA height to be nominated for the lowering of that height within 10NM MSA and leave the other 25NM MSA sectors at their current lower heights all the way to the aid, then it may make some approaches easier, such as the case for a night visual approach in Nadi rwy 02 (geographical constraints permitting) and eliminate the possibility for error.

Thoughts?

[Capt Claret]

What about the case of take-off, rather than arrival, where a performance loss is suffered and manoeuvring is required. A 10nm MSA allows one to stay within 10nm, at or above said MSA and manoeuvre to one's heart's content.

Some 10NM MSA are lower than some of the 25nm sectors, some are higher than the majority of sectors; eg CS NW 5200', NE 4000', S 6500' BUT 10nm 5600'.

Or, one can assess which sector one is and apply that MSA.

[Dr Reedalldabooks]

I see your point, but imagine that is could be specified that the S sector of 6500’ you were able manoeuvre 5600’ within 10NM where as the NE and NW sectors you on;y had to climb to 4000’ and 5200’ respectively. You could still manoeuvre to your hearts content but instead of climbing to 5600’ you could head out to the NE where we know there is no terrain and climb to the MSA of 4000’ 0-25NM as the chart would specified that the 5600’ only applied to lowering the southern 6500’ sector, not raising the other NW and NE sectors. Would be a win for arrival and departures with performance loss? All this assuming it was geography possible. If not, then make the 4000’ and 5200’ MSAs 5600’ as you would have to climb to 5600’ anyway within 10NM because that is the MSA. There would still be a note about 5600/10NM and you could still use this as in your example for lowering the 6500’ within 25NM height.

[Capt Claret]

I think you're making it more complicated than it is. I don't know NADI so will use CS as an example.

If manoeuvring ex CS in the NE sector, one only needs to climb to 4000 to be at the MSA. One doesn't have to climb to 5600' whilst within 10nm, unless one moves out of the 4000' sector lateral boundaries.

So, it's not a case of the highest MSA is the applicable one, rather, whether one wants to constrain one's flight to a sector and its MSA, or one wants freedom to manoeuvre.

Effectively one has four MSA at CS.


6500' is the highest of the published MSA, so one can manoeuver within 25nm without any terrain constraints.
5200' is the next highest 25nm MSA, in the NW sector. So, one could manoeuvre without terrrain constraints in the NW or NE sectors at or above 5200'.
4000' is the lowest 25nm sector, one can only manoeuvre within this sector at 4000' but one is constrained to stay between the 350 & 090 radials.
5600' gives terrain clearance out to 10nm regardless of sector.

[DeltaSix]

Dr R

The 25nm MSA covers the highest point within the splay of the track in that quadrant. The 10nm MSA covers the circle around the airport not on just one quadrant ( unless specified of course ). So, to have a higher 10nm MSA means that if someone is doing an instrument approach, the aircraft might cover (depending on the approach procedure ) the entire 10nm circle over the airport and might have an obstacle or a high point in either one of the quadrants to warrant a higher MSA.

So, if the 25nm MSA is lower, you will only use it if you think you can get a radar vector or clearance within 10nm. Otherwise climb to the higher MSA or stay at the higher MSA till you get further descent clearance or as a part of the instrument procedure.

If the airport does not have a serviceable DME then you will have to stay at the higher MSA.

D6

[Dr Reedalldabooks]

D6, I understand this. That is what I talk of when I mean geographically possible. What I am saying is that in some airports (overseas not in Oz – see my example for Mumbai) they do not do it this way. It might be perhaps they have different rules, I don’t know. They are able to specify that some sectors can go down to below others within 10 miles. If not why not just raise the 25NM MSA to the 10NM MSA as your are approaching the airport as you will have to climb to the 10NM MSA anyhow. I would also argue if you are doing an instrument approach, you would be flying the height constraints on the approach plate, not the MSAs (except for establishing yourself at the starting point for the instrument approach of course).

[ftrplt]

ENR 2.2.1

If the 25nm sector MSA is less than the 10nm MSA, the lower 25nm sector MSA can be maintained tracking to the aid as long as you remain inside the sector.

I.E; you DONT have to climb to the higher 10nm MSA if remaining inside the sector (and tracking to the aid)


P.S: a 2 minute search through the ASA on-line publications to find the reference, maybe a better first point of call than here??

[DeltaSix]

Ftrplt, that is correct. What I'm referring when to climb is if the holding pattern or the start of the instrument approach is usually the same altitude as the 10nm MSA and for some reason you are below that. But, personally if I know that I would be in the holding pattern, I'd stay on that altitude.

Dr R - It's for safety reason. That should give an aircraft in trouble ( say having one engine failed and cannot maintain altitude) to go down that low since the MSA will give a 1,000 feet clearance and hopefully rectify the problem or find a solution.

As the ENR says, you can stay in the lower MSA as long as you stay in that sector.

D6

[ftrplt]

agreed D6, I was only referring to the first question

[Ready Immediate]

I agree with Capt Claret - it is a departure issue as well. If you can't reach the track lowest safe by your circling area in IMC but you can reach the 10nm MSA then you only have to reach the track lowest safe by 10nm.

RI

[stainedpantystealer]

Point 1... Nadi is actually located on the Western cost of Fiji, not the Eastern!

Point 2... Doesn't it make perfectly normal sense that when a mix of high & low MSA's are designated, as is the case here, that there is a pretty good chance that the 10NM MSA will be higher than some of the 25NM MSA's as it comprises a 10NM sector in all directions as is the case here.

Point 3... Arrivals into Nadi are pretty straight fwd - you either get cleared to the MI NDB from the south and join straight onto the ILS, or from the North get cleared to NN VOR and join the ILS via the R204 reversal.

Touch down. Get beer in hand. Score a hot sweedish back packer down at Nadi Bay Hotel then drag it back to the hotel.

Done. Game over. Enough said!

Waaaaay toooo much effort gone into the original post!

Speaking of back packers.....

[DeltaSix]

So, stainedpantystealer, what possible pick up line can you give so you can pick up a hot Swedish packbacker and drag her down to your hotel for some hot swedish massage without discussing Ikea and Abba ?

What's the FMC setting again for the Nadi ?

[Fragnasty]

ftrplt,

Hear hear. If most of the clowns on here bothered to read and understand the relevant publications, this flying thing would be a piece of piss!

Choice 'bro!

[Dr Reedalldabooks]

Ftrplt: Thankyou, that was the rule I had missed. Thought as I was writing all that that there must have been some such rule for it to make more sense. I missed that, better read clearer next time! Do you know if this rule applies to other countries as well as Australia? (I will look it up later but for now, was wondering if you knew?)

Stainedpantystealer: Yes Nadi is on the west. Coast, all those east and west MSA sectors I got myself confused. Nadi was just an airport I used, I wasn’t saying it was inherently difficult to get in there. But thanks for the examples.

Fragnasty: Clown? Thanks for the compliment. Is this sort of attitude you treat everybody with who raises a question or a query about something in aviation? Bro?

[QSK?]

Dr R:
Do you know if this rule applies to other countries as well as Australia?
I don't have a copy of ICAO Doc 8168 (Pans-ops) handy at the moment but I am fairly sure that this standard in the Oz AIP has been lifted directly from the ICAO document, which implies that it may be adopted by other countries unless they lodge a formal difference.
Maybe others who have immediate access to 8168 can confirm, otherwise I will respond sometime tomorrow.

[Capt Claret]

Dr Reedalldabooks,

Have a look at the 10nm MSA. How many are not valid for 360 degrees around the station?

Then look at the plethora of 25nm MSA that are sectorised, as opposed to 360 degrees around the station and ask yourself the logical question; "If the 25nm MSA is the lowest level in a given lateral piece of airspace, that gives a minimum 1000' obstacle clearance, how can the 10nm MSA possibly require a pilot to climb?"

[Fragnasty]

Dr Reedalldabooks,

Yes.

[OzExpat]

Dr R

The same thing applies in PNG. Don't know whether other countries have followed suit though.

QSK?
which implies that it may be adopted by other countries unless they lodge a formal difference.
Not true. Differences only need to be filed against Annex requirements, not against specifications in a "Document". It's a subtle but important difference because Contracting States are only required to specify how they implement any particular document. This means, unfortunately, that you need to read the AIP for the particular country (i.e. Fiji, if taking the oiginal example), to find out whether or not they have implemented the Document in-toto or not.

The biggest problem with this is that one must know the contents of the relevant Document before studying the way in which a Contracting State has implemented it. In most cases, a State's implementation will only describe instances where a higher standard than that stated in the ICAO Document is used. The use of a lower standard is not regarded as an implementation of the ICAO specifications in the Document and I'm not aware of any Contracting State doing so.

[OzExpat]

By way of clarification of the reason why a difference can exist, there is a requirement to place a buffer around the lateral boundary of each MSA sector. This buffer extends right around the reference navaid.

I'm not sure how closely Oz follows Pans Ops in this respect but PNG uses a buffer that is 5 NM wide and Australia won't use a wider buffer than that.

This buffer is also applied around the distance limit, whether that be 25 NM or 10 NM. Therefore, the area which is surveyed for the 10 NM MSA is a radius of 15 NM. This is obviously far larger than the buffer around the navaid, as used for the 25 NM MSA sector, because the only protection around the reference navaid is a radius of 5 NM.

Accordingly, an obstacle can exist at any distance greater than 5 NM, up to 15 NM and not affect the protection for the 25 NM sector MSA, but will certainly affect the 10 NM MSA.

[QSK?]

OzExpat:

You're absolutely correct re lodgining of differences. For some reason, I thought differences were also required to be lodged for "standards" contained within ICAO Docs as well as Annexes. Thanks for pointing out my error.

Cheers QSK?

[OzExpat]

Nurries mate. Over the years, I've seen a lot of confusion on this and it's primarily created because ICAO Documents are always based on one, or more, of the Annexes. As ICAO says, the Documents contain technical information that is beyond the scope of the Annex (or words to that effect).

Thus, the inevitable result is that people erroneously associate Documents with Annexes in the need to file differences. I get confused just talking about it! :eek:

[JAR]

I haven't read all the above, but 25 nm MSAs are based on IAF and 10nm on the aerodrome. Therefore if IAF is a VOR located some way from airport then MSAs will be different.

[OzExpat]

Not sure that I'd agree with that JAR. For a start, the 25 MSA isn't necessarily based on the IAF - to make such an assumption could give you a real "bad hair day". As with the 10 MSA, the 25 MSA is based on whatever the chart says it's based on.

[JAR]

From Jeppeson MSA is defined as "....within 25 nm radius from the navigational facility upon which the MSA is predicated."
Granted, not always, but more often than not, the IAF.:ok:

[NOtimTAMs]

.....except for those with GNSS RNAV approaches only, where the MSA is centred on the ARP - don't know if an ARP counts as a "navigation facility", but. ;)