Descending to the 25nm MSA

[ooizcalling]

Situation; You are flying over an area of relatively high terain prior to your destination where the lowest safe altitude (route or grid MORA etc) is well above the destinations 25nm radius MSA and also well above the IAF altitude for the let down you will use. The weather is IMC and you will have to do the letdown to the field/rwy. The question is, can you descend below the route MEA/ grid MORA or whatever limit was the restriction en route down to a lower 25nm MSA when established inside the 25nm range to facilitate direct entry into the let down proceedure rather than maintaining your lowest possible route altitude limit to the holding pattern and then descending?

I've been using this technique for years but was recently told by a Route Instructor that the 25nm MSA is defined for 'Emergency Use Only' and therefore not available for such purposes under 'Normal Operations'.

So is this true or not ? (under JAA/OPS in Europe), and ...

If this is true, then what is the difference in the survey quality of the 25nm MSA verses the other minimum altitudes that limits it to 'Emergency Use Only'.

There's no logic in this limitation under my current understanding of the various altitude limitations. Can anyone assist ?

[Captain Stable]

The MSA's shown on en-route charts are just that - en-route MSA's.

Within 25nm of the field and either under positive radar control or following a published procedure, your MSA is that shown on the approach plate.

[Tinstaafl]

Nowhere in the documentation is the 25nm MSA described as 'for emergency use only'.

It's what it says on the tin: Minimum altitude available for use in that sector giving a defined amount of terrain separation.

[BOAC]

IMHO, ooiz, your "Route Instructor" is talking out of his/her 'vent'! Do, however, adopt the simple step of asking for the origin of this 'rule', then please publish it so that if we are ALL wrong, we can learn.

[Blue Heeler]

The 25NM MSA is a normal provision under PANS-OPS. It is published to facilitate descent for the IAL procedure. Of course it is also useful in an emergency, but your Route Instructor is quite wrong in associating the MSA with emergency procedures.

[FIRESYSOK]

Ive heard foreign operators brief a 100nm safety altitude for the departure. Is this an MEA for the routing. In the US, we use the 25nm MSA for use after takeoff for returnability. Do European charts show the 100nm MSA? Thanks.

[reynoldsno1]

The history of the 25nm sector altitude is that it was originally devised for aircraft in an emergency situation. Pilots recognised early on that it was also had other uses - arrival planning is an obvious example - and nowadays it is used primarily as an orientation/planning aid. You get a minimum 300m (1000ft) terrain separation in each sector (up to 600m, 2000ft in mountainous terrain).

I think Europe is too small to accommodate 100nm sector altitude charts!

[ooizcalling]

I am aware of the so-called 100 nm Emergency Safe Altitude. I understand it's the minimum altitude within 100 nm of the field in question that provides 1000 ft clearance of all obstacles to 6000 ft and 2000 ft clearance to obstacles above 6000 ft within that radius (and that is a huge area !) The European IAL charts produced by the joint KLM/SAS/Swissair group have that data on them.

It would seem most have my interpretation of the 'practical' use of the 25nm MSA is common, but I have just found the reference I've been looking for, .... The Route Instructor would appear to be correct.... Dam !;

The Jeppesen, Introduction, Chart Glossary section reads as follows;


MINIMUM SAFE ALTITUDE (MSA) - Altitude depicted on an instrument approach chart and identified as the minimum safe altitude which provides 1000-foot obstacle clearance within a 25NM radius from the navigational facility upon which the MSA is predicated. If the radius limit is other than 25 NM, it is stated. This altitude is for EMERGENCY USE ONLY and does not necessarily guarantee NAVAID reception. When the MSA is divided into sectors, with each sector a different altitude, the altitudes in these sectors are referred to as "minimum sector altitudes".

So there it is ! The caveat seems to be the lack of guarantee of navaid reception and not to do with the quality of the survey within the 25nm.

How then can a pilot determine if the acceptable level of NAVAID reception is being achieved. eg what about a GPS position that's independant of the terrestrial NAVAID?

Interesting eh !

[FIRESYSOK]

Very cool. Thanks for the research!:p

[Blue Heeler]

Ooizcalling, maybe that is so in your country, but it is not the general case.

Jeppesen is not the authority so presumably the description of the MSA is taken from your AIP.

PANS-OPS definitions:
Minimum sector altitude. The lowest altitude which may be used which will provide a minimum clearance of 300 m (1000 ft) above all objects located in an area contained within a sector of a circle of 46 km (25 NM) radius centred on a radio aid to navigation.

PANS-OPS Vol 1 Part 3
3.2.1 Omnidirectional or sector arrivals can be provided taking into account minimum sector altitudes (MSA) (see 1.2.5).

1.2.5 Minimum sector altitudes are established for each aerodrome and provide at least 300 m (984 ft) obstacle clearance within 46 km (25 NM) of the homing facility associated with the approach procedure for that aerodrome.

[ooizcalling]

Hello Blue Heeler, I've only recently gone back to using Jepp charts in which this 'Emergency Use Only' is stated. Previous IAL charts I have used (non Jepp.) have not had this restriction, or at least I can't remember it, and like I say, I've taken advantage of a lower MSA as a standard proceedure to facilitate entry into the IAL proceedure or even becoming visual at that lower MSA. However it IS on the glossary of the Jepp charts as a restriction. It's probably a factor that affects < 1% of IAL's but tossed in there to cover Jeppesen from a legal point, but seeings we use Jepp charts and this restriction covers all of them, I guess from that same legal viewpoint, I'm bound by it. It's dam anoying to have a practical application made illegal to satisfy a technicality. I can't see a way around it at the moment that gives me the option to legaly use it. Can you ?

[Blue Heeler]

Ooiz.

I am on leave at the moment and don't have Jepps handy, but I will look at the Oz Jepps when I get back. They should not have any reference to "emergency" as PANS-OPS is applied in Australia and Ozzie rules consider the use of MSA to be a "normal" procedure.

What I was suggesting is that the view of the regulatory authority where you are may be different, and that Jepps are probably reflecting that view. Rather than taking Jepps at face value I was suggesting that you search the "source" regs for the answer to your original question.

I'd be interested to know the result. Most European countries apply PANS-OPS so the idea of the MSA being an emergency procedure is curious.

[Crossunder]

Since PANS OPS doesn't define MSA as an emergency altitude it is not an emergency altitude. I've also used both SAS Flight Support's and Jeppensen's IALs. My personal view is that Jeppesen, being American, always put a lot of un-necessary restrictions and pointless information on their plates to avoid any legal actions from the fortune-seeking american lawyers. I suspect this "emergency altitude" designator is one such precaution...

[reynoldsno1]

Just a couple of points:

1. PANS OPS is an ICAO manual, and offers guidelines for instrument procedure design. It does not have the same status as a Standard & Recommended Practice. Individual States may specify different criteria (e.g. the New Zealand AIP states that the 25nm MSA is for emergency purposes)

2. The 25nm MSA does not guarantee navigation aid reception.

3. FAA TERPS criteria specify that the 25nm MSA is for emergency purposes.

OK, that's three....

[Blue Heeler]

Reynolds01

Exactly. In order to resolve the original question put by Ooizcalling it is necessary to find out what the individual State's position is.

Mind you the reason why some States (who use PANS-OPS) appear to regard the 25NM MSA as an emergency altitude is puzzling.

[RatherBeFlying]

Perhaps it's something to hang your hat on after you've missed and lost comms while you're sorting out a gear problem.

[Girt_bar]

From the "Aviation Theory Centre Training Manual - IR LAW". The New Zealand version

"The purpose of the information on the 25nm minimum sector altitude diagram is to provide the pilot with a quick minimum safe altitude within a sector when an emergency situation in IMC has developed. A lower altitude may be flown within the area when the aircraft is following a promulgated route, a published flight procedure with a lower MSA, or VORSEC information."

NB. All NZ procedures (except two i believe) are based on PANS OPS II.

Not sure about the rest of the world.

[reynoldsno1]

For the uninitiated, the NZ VORSEC Minimum Reception Altitude (MRA) chart is similar to the 25nm MSA chart except that it normally extends to 40nm and the minimum altitudes depicted are based on navigation aid reception. It is specifically designed to assist arrival planning.

I think the crucial point is that the 25nm MSA does not guarantee navaid reception, and that is probably why many States designate it for emergency use only.

[OzExpat]

The PNG AIP does not use the term "emergency" in its' various references to MSA. Of all the navaids upon which a MSA is based, only one has a rated coverage of less than 25 NM. That one's a special case though and, having been originally installed more recently than any of the others, we weren't about to change our MSA definition for the sake of that one navaid.

PNG publishes rated coverage for NDBs and Locators, and quotes an assumed range for VORs of 60 NM. I would be very disapponted if Jeppesen, or any similar organisation, has taken the liberty of adding the word "emergency", when describing our MSA criteria.

[reynoldsno1]

I would be very disapponted if Jeppesen, or any similar organisation, has taken the liberty of adding the word "emergency", when describing our MSA criteria.

They haven't. They also include an explanatory note about your 10nm MSA depiction.

[OzExpat]

Thanks reynoldsno1. Would you happen to know if they also provide an explanation of the 5 NM IAWP MSAs on our GPS approach charts? I know that you know about them! :D

[reynoldsno1]

They don't appear to do so at the moment....:)

[OzExpat]

Thanks for that - they're probably still just coming to terms with the 10 NM MSA within 25 NM MSA circle! :D

[Fuji-san]

Just having a look at the RACAL No.1 AIDU(RAF)/RACAL(AERAD)
TERMINAL CHARTS SPECIFICATION & LEGEND BOOKLET.

PART 1 : CHARTS SPECIFICATION

DESIGN :

25. Minimum Sector Altitude (MSA) cicles are taken from State AIP, or in the case of British military airfields, calculated by AIDU. An MSA is the lowest altitude which may be used under Emergency Conditions.............................

So it would seem to apply to non - jep charts too !!

A surprise to me :confused:

[ooizcalling]

I havent been able to research this any further but it would seem that the 'EMERGENCY USE ONLY' qualification is due to the Nav Aid reception limitations rather than the quality of the survey of obstruction altitudes within the 25 nm radius.

What I'd like to get a definative answer on is the use of that 25 nm MSA in Normal Operations where either;

1) No limitation is given on the Navaid Reception that affects the defined area at or above the specified altitude OR
2) Where you have an independant means of knowing that your position with certanty lies within the 25 nm. eg. a GPS position and I guess at this stage it is still an en-route part of the flight and therefore an En Route certified receiver would satisfy the position criteria.

Wonder if I'll ever get that definative answer ?

[reynoldsno1]

ICAO Document 8168 Vol II Part III Ch. 3 states that omnidirectional or sector arrivals can be provided taking into account the MSA. Specifically for GNSS approach procedures, where no specified arrival route is published, it is recommended that a single sector MSA is published to facilitate arrivals. The MSA is based on the ARP co-ordinates.

[OzExpat]

No, ooizcalling, you probably won't get the definitive sort of answer that you're looking for. This is because different countries have different philosophies. In the approaches that I design for the PNG CAA, the 25 NM MSA is available as a normal part of the approach. We even allow the use of distance information from a TSO-129 IFR GPS Receiver, in enroute mode, for determining position within the MSA.

In fact, we allow unrestricted use of IFR-certified GPS Receivers, for all navigational guidance at the lower of the route LSALT or MSA. Our only condition is that the reference point to be used by the GPS Receiver MUST be the destination's prime azimuth navaid. And, of course, RAIM must be available.

I don't know if any other regulators have gone that far with their approvals.

[Tree]

If you are operating in a mountainous environment I do not recommend using the 25 nm msa for other than emergency purposes. If used for emergency purposes in winter you must correct for temperature deviation. Since the 25 nm msa only guarantees 1000ft. above terrain a moderately cold day without correction will acquaint you with your last emergency in flying called cumulo-granite!
Stay on the mea (also correct it for temp. deviation) to the fix and then descend accordingly.
Just my opinion based on decades of experience with 8 legs per day.

[OzExpat]

Horses for courses, Tree... I'm in an extremely mountainous environment but the temperature is almost always between ISA +15 and ISA +20 and never, ever, colder than ISA.

[PositiveCLB]

MSA does not guarantee radio reception. Cheers

[Old Smokey]

PANS-OPS provides for 1000 feet of vertical separation from obstacles within 25 nm of the defined reference point. 1000 feet is accepted as the minimum altitude for NORMAL operations. Every minimum altitude must be temperature compensated in colder than ISA conditions, that's still NORMAL. Being in an area of Navaid uncertainty is not an emergency.

Emergency altitude clearance covers situations such as engine failure, where FAR 25 and all of it's equivalents, not PANS-OPS, apply. This provides for 35 feet obstacle clearance from the Net flight path, a true emergency. A properly designed One Engine Inoperative "Escape Procedure" will comply with the much lesser FAR 25 EMERGENCY obstacle clearance requirements until MSA is reached, whereupon PANS-OPS separation applies, and the emergency phase is over.

Regards,

Old Smokey

[haughtney1]

So have we yet established that if you descend to sector safe MSA...your not gonna hit anything solid?:uhoh:

[tescoapp]

What do the old and wise do about adjusting MSA for wind speed?

Or for that matter do ATC take account of it when producing min vector charts?

[chevvron]

MSAs appear on Radar Minimum Altitude Charts (RMACs) in the UK. As far as ATC are concerned, aircraft may be descended to the minimum altitudes shown and still maintain correct terrain clearance, whether in emergency or not. You should get copies of RMACs with your Jeppesen/AERAD packs for each airfield which has an RMAC published; the chart has to be approved by UK CAA.

[tescoapp]

But do you as controllers take into account below ISA temp or high winds?

Or is it all factored into the min vector charts.

BTW the vector charts are no use to man nor beast because they don't have a scale on them. The limits if you are lucky have some physical feature nearby ie a mast or hill etc.

Its a catch 22 situation you can only know where the limits are when you can see the ground to see the features. But when you can see the ground you don't care because you can see the ground.

As an example if you had a 70knot wind at 3000 feet at ISA -10 you could have to add 300ft to your MSA (don't have the tables here) on the approach to 24R at MAN on a 12 mile final. Added to which you can have the standard 149ft mast without planning permission thats dropped you down to 550ft clearance.

[Clandestino]

The question is, can you descend below the route MEA/ grid MORA or whatever limit was the restriction en route down to a lower 25nm MSA when established inside the 25nm range to facilitate direct entry into the let down proceedure rather than maintaining your lowest possible route altitude limit to the holding pattern and then descending?


No.

If you're doing procedural arrival, stick to min alts published on STAR chart. MSA caters only for terrain clearance while MEA takes care of terrain clearance, navaid reception and airspace restrictions. So busting MEA and going down to MSA will keep you away from terrain, but you might find yourself in the one of the following: G class airspace, (para)glider area, CTR, restricted area, dangerous area or even military ACM range. Luckilly, there are not many MEAs higher than MSAs in mountainuous areas. The only one I came across was due to three levels we could use being resrved for fellow aviators not equipped with transponders, but fairly equipped with live sidewinders (AIM-9s, not the reptiles).

While vectored, it's ATC responsibility to keep you separated from terrain and special use airspace, so MSA/MEA is of no relevance here. Also Jepp's MRVA charts are drawn to scale and I find them easy to read and check your position against them.

[chevvron]

Are the Jepp charts not included in FMS software then?

[312f1c291081b20c22ba]

If you look in the 2007 FAR/AIM on page 706 top of the page left side, you will find your route instructor is correct. Read the first two lines "The (MSA) are published for emergency use on IAP charts." We were taught that in the Navy and it is taught at flight schools. The route instructor is correct as far as the USA goes.

[SNS3Guppy]

312f1c291081b20c22ba,

The "FAR/AIM" is a commercial pulbication, not a government publication, which is produced by several companies, and includes copies of several different government documents. The "FAR" portion is selected parts of the Code of Federal Regulations, and the "AIM" includes generally the entire Aeronautical Information Manual. However, the page numbers don't mean much because different companies publish it differently and in different forms, and different parts. There are numerous "FAR/AIM"'s, and they're each different in content and arrangement, in any given year.

MSA is published as a reference for emergency use, in that it's an altitude you need to be aware of in the event you need a quick and dirty reference to keep you clear of terrain.

You're generally best to stick to the published route, arrival, or procedure altitudes, rather than freelancing at the minimum published, particularly the MSA. It's chief purpose is not as a planning tool for arrival or departure (or transit), but as a reference is you need a minimum altitude in an emergency.

For those utilizing an arrival to a field where there is not arrival structure, such as transition from an airway or arrival procedure, the use of a cruise clearance coupled with a contact approach (USA specifically, in this case) is one function where the use of the MSA becomes a handy reference.

As others have noted, great caution is to be advised at all times, but particularly so in mountanous terrain, and particularly in cases of lower than standard pressure or temperature, or in times of transition from one area of higher pressure to lower pressure. The Aeronautical Information Manual, for example provides for obtaining the nearest altimeter setting within 100 nautical miles; I've seen the altitude change by 1,000' within a short 50 mile trip before in a stormy frontal area...effectively eliminating the terrain clearance and any margin of safety one might hope to obtain from the MSA.

Personally, particularly in the terminal area, I'm not going to descend until I'm established on a published part of the enroute, arrival, or terminal procedure. If something goes wrong, the MSA is there for a quick and dirty reference, but I'm not going to predicate an arrival descent or a departure climb on that.

[PicklePilot]

The safest option is to hold the MEA all the way to the fix, then descend in the approach, or descending in the holds to get to a civilized altitude to execute the approach... MSA is your rock bottom, don't go lower then this point thing...

[bArt2]

I do not really get the point of the question as under normal circumstances you would stick to the published altitudes on the approach plate, or the altitudes you are cleared to by ATC
I have never done an arrival where I have chosen myself what altitude to descend to, unless I would be NORDO in which case you would have an emergency.Here are the definitions published in the USAF General Planning (GP)


MINIMUM SAFE ALTITUDE/MSA (P/CG) -
(1) The minimum altitude specified in Federal Air
Regulations Part 91, for various aircraft operations.
(2) Altitudes depicted on approach charts which
provide at least 1000 feet of obstacle clearance for emergency
use within a specified distance from the navigation facility upon
which a procedure is predicated. These altitudes will be identified
as Minimum Sector Altitude or Emergency Safe Altitude and are

established as follows:
(a) MINIMUM SECTOR ALTITUDES - Altitudes


depicted on approach charts which provide at least 1,000 feet of

obstacle clearance within a 25-mile radius of the navigation facility

upon which the procedure is predicated. Sectors depicted on

approach charts must be at least 90 degrees in scope. These

altitudes are for emergency use only and do not necessarily assure

acceptable navigational signal coverage.

(b) EMERGENCY SAFE ALTITUDES - Altitudes

depicted on approach charts which provide at least 1,000 feet of

obstacle clearance in non-mountainous areas and 2,000 feet of

obstacle clearance in designated mountainous areas within a 100-

mile radius of the navigational facility upon which the procedure is

predicated and normally used only in military procedures. These

altitudes are identified on published procedures as "Emergency

Safe Altitudes".

MINIMUM SECTOR ALTITUDE (ICAO) - The lowest altitude which
may be used under emergency conditions which will provide a
minimum clearance of 300 meters (1000 feet) above all obstacles
located in an area contained within a sector of a circle of 25 nautical
miles radius centered on a radio aid to navigation.

[jeff737]

hi
can you tell me for a MSA
what is the lateral distance protection? it is also 300m like vertical

thank you