Descending to the 25nm MSA
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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! 
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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
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
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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 ?
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 ?
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.
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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.
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.
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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.
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.
Last edited by Tree; 8th Mar 2003 at 18:07.
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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.
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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
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
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.
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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.
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.
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?
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.
Last edited by Clandestino; 20th Oct 2006 at 22:09. Reason: Typo
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MSA Circle
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.
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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.
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.
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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...