Descending to the 25nm MSA
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Descending to the 25nm MSA
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 ?
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 ?
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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.
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.
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.
It's what it says on the tin: Minimum altitude available for use in that sector giving a defined amount of terrain separation.
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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.
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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.
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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.
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!
I think Europe is too small to accommodate 100nm sector altitude charts!
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The Route Instructor was right !
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 !
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 !
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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.
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.
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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 ?
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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.
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.
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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...
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....
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....
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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.
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.
Perhaps it's something to hang your hat on after you've missed and lost comms while you're sorting out a gear problem.
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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.
"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.
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.
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.
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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.
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.
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.