Minimum Safe Altitude
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Minimum Safe Altitude
hello
could anyone tell me how i work out the minimum safe altitute by looking at my map.
im a student doing my ppl and would be glad of some advice and knowledge from you all.
Thanks in advance
Craig
could anyone tell me how i work out the minimum safe altitute by looking at my map.
im a student doing my ppl and would be glad of some advice and knowledge from you all.
Thanks in advance
Craig
You can do a Grid MORA by looking on your map. On the map the are blue numbers that tell you the higest object in that square and add 1000ft or more convient is a route MORA which is the highest object within 5NM either side on your route not forgetting the ends of your route, add 1000ft. Some people will tell you to add 300ft on top of that as any object that is less then 300ft is shown.
Assuming you're looking at a CAA Chart:
Large blue numbers mark the Maximum elevation figures for each "quadrangle" (CAA term -1/2 degree lat/long squares on the 1/2 mill chart). That shows the height AMSL of the highest known feature or terrain.
Add a 1000' safety margin to that , and you get your MSA for that quadrangle.
Of course if you're flying VFR, 500' away from any obstacle will do
Large blue numbers mark the Maximum elevation figures for each "quadrangle" (CAA term -1/2 degree lat/long squares on the 1/2 mill chart). That shows the height AMSL of the highest known feature or terrain.
Add a 1000' safety margin to that , and you get your MSA for that quadrangle.
Of course if you're flying VFR, 500' away from any obstacle will do
Last edited by Mariner9; 28th Sep 2005 at 16:11.
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There are no hard and fast rules for VFR (there is for IFR). One reasonable rule is to add 1000' to the heighest obstacle within 10nm of your track (some use 5nm).
The heighest obstacle is:
* Terrain Height + 300' (because anything under 300' isn't shown on the CAA VFR charts.
* The height above the terrain of any recorded obastacles. The chart shows two figures for each obstacle: one in brackets is the actual height, the one out of brackets is the total height - the one you are usually interested in.
The quick and easy method is to look at the pre-determined Maximum Elevation Figures (MEF) as marked on the chart within each lat/long bounded quadrant. The numbers show thousands and hundreds to the nearest hundred feet and show the heighest obstable altitude (as calculated above) in that rectangle. All you need to do is look along your track, get the biggest number and add 1000' to it (again within 10nm).
*NOTE: The average male thumb is 10nm 1:500,000 chart. Very useful for all sorts of navigation as well as a quick MSA lookup should you need to divert unexpectedly!!
**NOTE: The MEF on the CAA charts require you to add 1000'; some other VFR charts like Jeppesen don't require you to add 1000'.
The heighest obstacle is:
* Terrain Height + 300' (because anything under 300' isn't shown on the CAA VFR charts.
* The height above the terrain of any recorded obastacles. The chart shows two figures for each obstacle: one in brackets is the actual height, the one out of brackets is the total height - the one you are usually interested in.
The quick and easy method is to look at the pre-determined Maximum Elevation Figures (MEF) as marked on the chart within each lat/long bounded quadrant. The numbers show thousands and hundreds to the nearest hundred feet and show the heighest obstable altitude (as calculated above) in that rectangle. All you need to do is look along your track, get the biggest number and add 1000' to it (again within 10nm).
*NOTE: The average male thumb is 10nm 1:500,000 chart. Very useful for all sorts of navigation as well as a quick MSA lookup should you need to divert unexpectedly!!
**NOTE: The MEF on the CAA charts require you to add 1000'; some other VFR charts like Jeppesen don't require you to add 1000'.
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I think the answer that is expected from a PPL is that one draws the track line on the chart, and looks 5nm either side of it, take the highest obstacle found, add 1000ft to it, round the answer up to the next 100ft, and that becomes the MSA for that entire leg of the route.
If the elevation is above 5000ft (unlikely in England!) then add 2000ft instead of 1000ft.
That's what I was doing in 1999 and that's what I do for VFR and IFR today.
HWD beat me partly to it, but once one starts getting into non-CAA charts then one needs to be a whole lot more careful. I've seen charts (e.g. Swiss ICAO, get them by mail order from Skyguide along with the Swiss VFR touring guide) which contain a mixture of feet and metres and it's not obvious! If you are flying VFR, the hills just look a lot bigger than expected..............
It's true that there is no MSA requirement for VFR but without a planned MSA one is right up the s**t creek if the vis becomes bad (e.g. heavy rain).
If the elevation is above 5000ft (unlikely in England!) then add 2000ft instead of 1000ft.
That's what I was doing in 1999 and that's what I do for VFR and IFR today.
HWD beat me partly to it, but once one starts getting into non-CAA charts then one needs to be a whole lot more careful. I've seen charts (e.g. Swiss ICAO, get them by mail order from Skyguide along with the Swiss VFR touring guide) which contain a mixture of feet and metres and it's not obvious! If you are flying VFR, the hills just look a lot bigger than expected..............
It's true that there is no MSA requirement for VFR but without a planned MSA one is right up the s**t creek if the vis becomes bad (e.g. heavy rain).
Why do it if it's not fun?
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This seems to be an area where many of my students get very confused.
The first thing to understand is what the MSA is. It is an altitude, at or above which you are guaranteed to be safe from hitting the terrain. That does not mean it's not safe, legal or correct to fly below that altitude. It does not mean it is legal to fly, or plan to fly, at or above that altitude (at least not without the correct permission).
Take, for example, the Manchester Low Level Route. The route must be flown not above 1250'. Many of my students who do not understand the concept of MSA correctly therefore think that the MSA must be below 1250'. This is not true. In the case of the LLR, the MSA is something above 1250' (I don't have a chart to hand to confirm exactly what it is).
You may plan to fly the route at 1100', which is both safe and legal, but below your MSA. If, as you are flying down the route, you inadvertently enter clouds, your first reaction should be to note that you are below the MSA, and should therefore climb to the MSA in order to be certain of not hitting anything on the ground. Of course, this climb will take you into controlled airspace, so your next reaction should be to inform Manchester Approach that you have inadvertently entered IMC and are climbing. (A Mayday would be appropriate in this situation if you are not qualified to fly on instruments.)
Ok, so now that's cleared up, how do you calculate the MSA?
As Scuba said, there are 2 basic methods. The first involves using the Grid Maximum Elevation figures. These are the big blue numbers on your chart - one in every latitude/longitude rectange. This will give you the highest known elevation anywhere in the rectangle, so find the highest one, and then add 1000' on to that to give you a safe altitude.
The second method involves tracing along your route, finding the tallest object within a certain distance of your track. This distance should be at least 5nm. This method takes a little longer, but gives a more realistic and less conservative figure. Again, you need to add 1000' to the highest object you find to give you a safe altitude.
But there is an extra complexity with the second method, and this is the 300' which Scuba mentions. The chart designer shows you any structures which are more than 300' tall, so if there is nothing shown on your chart you can assume that there are no structures taller than that. But there may be a 299' structure on the highest piece of ground you identify. So you should add 300' to all ground elevation figures to take account of this. On the other hand, if your track takes you past tall masts which are marked on the chart, there is no need to add this 300', because there will not be a 299' structure built on top of a mast.
If you use the first method of calculating the MSA - using the Maximum Elevation figures from the chart - there is no need to worry about adding 300', because the chart designer has already done this for you.
FFF
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[Edit to note that in the time it took me to type this, a couple of other replies appeared - I agree with all of them]
The first thing to understand is what the MSA is. It is an altitude, at or above which you are guaranteed to be safe from hitting the terrain. That does not mean it's not safe, legal or correct to fly below that altitude. It does not mean it is legal to fly, or plan to fly, at or above that altitude (at least not without the correct permission).
Take, for example, the Manchester Low Level Route. The route must be flown not above 1250'. Many of my students who do not understand the concept of MSA correctly therefore think that the MSA must be below 1250'. This is not true. In the case of the LLR, the MSA is something above 1250' (I don't have a chart to hand to confirm exactly what it is).
You may plan to fly the route at 1100', which is both safe and legal, but below your MSA. If, as you are flying down the route, you inadvertently enter clouds, your first reaction should be to note that you are below the MSA, and should therefore climb to the MSA in order to be certain of not hitting anything on the ground. Of course, this climb will take you into controlled airspace, so your next reaction should be to inform Manchester Approach that you have inadvertently entered IMC and are climbing. (A Mayday would be appropriate in this situation if you are not qualified to fly on instruments.)
Ok, so now that's cleared up, how do you calculate the MSA?
As Scuba said, there are 2 basic methods. The first involves using the Grid Maximum Elevation figures. These are the big blue numbers on your chart - one in every latitude/longitude rectange. This will give you the highest known elevation anywhere in the rectangle, so find the highest one, and then add 1000' on to that to give you a safe altitude.
The second method involves tracing along your route, finding the tallest object within a certain distance of your track. This distance should be at least 5nm. This method takes a little longer, but gives a more realistic and less conservative figure. Again, you need to add 1000' to the highest object you find to give you a safe altitude.
But there is an extra complexity with the second method, and this is the 300' which Scuba mentions. The chart designer shows you any structures which are more than 300' tall, so if there is nothing shown on your chart you can assume that there are no structures taller than that. But there may be a 299' structure on the highest piece of ground you identify. So you should add 300' to all ground elevation figures to take account of this. On the other hand, if your track takes you past tall masts which are marked on the chart, there is no need to add this 300', because there will not be a 299' structure built on top of a mast.
If you use the first method of calculating the MSA - using the Maximum Elevation figures from the chart - there is no need to worry about adding 300', because the chart designer has already done this for you.
FFF
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[Edit to note that in the time it took me to type this, a couple of other replies appeared - I agree with all of them]
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thanks
Hello gentlemen
A huge big thank you or all of those who have taken the time to reply to my post it has been very helpfull, i will print the forum off and do abit on MSA tonight with my mate and equipment.
Again thank you.
Craig
A huge big thank you or all of those who have taken the time to reply to my post it has been very helpfull, i will print the forum off and do abit on MSA tonight with my mate and equipment.
Again thank you.
Craig
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Definitive answer from FFF, who puts it all very lucidly.
Student~C150: One extra point: choose a particular chart series and stick to it at this stage. Until you have a feel for it all, instinctively, there is no point running the risk of being confused by the assumptions made by differing cartographers and designers. Personally, I'd go for the CAA 1:500000 series, though some FTOs prefer you to use the 1:250000 at your stage of training.
I'd be delighted to go through all the ground stuff with you sometime, but suspect we live too far apart. Nevertheless, if you're ever up this way, you're welcome to PM me to arrange a pint with charts, etc..
Of course, if you get stuck into ground school, you won't need the mentoring. Have you reached a decision on that?
Student~C150: One extra point: choose a particular chart series and stick to it at this stage. Until you have a feel for it all, instinctively, there is no point running the risk of being confused by the assumptions made by differing cartographers and designers. Personally, I'd go for the CAA 1:500000 series, though some FTOs prefer you to use the 1:250000 at your stage of training.
I'd be delighted to go through all the ground stuff with you sometime, but suspect we live too far apart. Nevertheless, if you're ever up this way, you're welcome to PM me to arrange a pint with charts, etc..
Of course, if you get stuck into ground school, you won't need the mentoring. Have you reached a decision on that?
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I usually just use the MEF + 1000, unless I need to fly lower than this to get under controlled airspace, such as London TMA. In that case I'd look a little closer to see if I can get my MSA below the base of the controlled airspace, so I'd never have to climb into it.
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EGTC,
The MSA is not a prohibative altitude when VMC. The idea is to provide a yardstick by which you may more objectively decide that you should not proceed if you find the cloud base is moving below the MSA.
In addition, if you were to inadvertantly find yoursel in IMC, it is the altitude you should climb to if below (to provide a reasonable level of leeway for a somebody whose workload just shot up) or descend to when above (to minimise icing). For those reasons, you should determine the MSA regardless of the airspace you will be travelling in/under/over. Once you are in an IMC situation for which you are not rated, issues such as being in the Class A TMA are a very distant second
I usually just use the MEF + 1000, unless I need to fly lower than this to get under controlled airspace
In addition, if you were to inadvertantly find yoursel in IMC, it is the altitude you should climb to if below (to provide a reasonable level of leeway for a somebody whose workload just shot up) or descend to when above (to minimise icing). For those reasons, you should determine the MSA regardless of the airspace you will be travelling in/under/over. Once you are in an IMC situation for which you are not rated, issues such as being in the Class A TMA are a very distant second
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The other thing is that without accurate navigation, MSA means nothing.
I bet it's a common mistake to carefully work out the MSA for some route, and then change the route. One might change it as a result of getting a transit through some bit of CAS.
If VMC, in England-type flat terrain, it should still be OK because one isn't knowingly going to fly into a hill. But in IMC....
Situational awareness comes into this heavily.
I bet it's a common mistake to carefully work out the MSA for some route, and then change the route. One might change it as a result of getting a transit through some bit of CAS.
If VMC, in England-type flat terrain, it should still be OK because one isn't knowingly going to fly into a hill. But in IMC....
Situational awareness comes into this heavily.
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Watch out for confusion between CAA and Jepp VFR GPS Charts. Former give MEF figures so - as otehrs have explained - you need to add VFR or IFR safety margins. Jepps already include a 1000ft margin.
In my view this lack of standardisation is very unclever as it could lead to a critical misjudgement. Consider coming back from the continent with Jepp charts on a long flight, reverting to CAA charts on entry to UK airspace then encountering low vis/cloudbase and being a bit tired and who knows how it might end.
In my view this lack of standardisation is very unclever as it could lead to a critical misjudgement. Consider coming back from the continent with Jepp charts on a long flight, reverting to CAA charts on entry to UK airspace then encountering low vis/cloudbase and being a bit tired and who knows how it might end.
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High Wing Drifter,
I do understand. But by trying to keep my MSA below controlled airspace, even if I do need to climb up to it after accidentally going into IMC, then I won't bust anyones zone. Having said that, if in IFR conditions accidentally it may be safer in controlled airspace where they can see you on radar along with all other aircraft.
I do understand. But by trying to keep my MSA below controlled airspace, even if I do need to climb up to it after accidentally going into IMC, then I won't bust anyones zone. Having said that, if in IFR conditions accidentally it may be safer in controlled airspace where they can see you on radar along with all other aircraft.
There is no such thing as MSA when VFR! You avoid obstacles visually.
MSA for IFR is in Rules of the Air Rule 39
Minimum height
29 Without prejudice to the provisions of rule 5, in order to comply with the Instrument
Flight Rules an aircraft shall not fly at a height of less than 1000 feet above the highest
obstacle within a distance of 5 nautical miles of the aircraft unless:
(a) it is necessary for the aircraft to do so in order to take off or land;
(b) the aircraft is flying on a route notified for the purposes of this rule;
(c) the aircraft has been otherwise authorised by the competent authority; or
(d) the aircraft is flying at an altitude not exceeding 3000 feet above mean sea level
and remains clear of cloud and in sight of the surface.
How you get that off your map is up to you!
MSA for IFR is in Rules of the Air Rule 39
Minimum height
29 Without prejudice to the provisions of rule 5, in order to comply with the Instrument
Flight Rules an aircraft shall not fly at a height of less than 1000 feet above the highest
obstacle within a distance of 5 nautical miles of the aircraft unless:
(a) it is necessary for the aircraft to do so in order to take off or land;
(b) the aircraft is flying on a route notified for the purposes of this rule;
(c) the aircraft has been otherwise authorised by the competent authority; or
(d) the aircraft is flying at an altitude not exceeding 3000 feet above mean sea level
and remains clear of cloud and in sight of the surface.
How you get that off your map is up to you!
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Right on Whopity,
MSA is only applicable once you have at least done your IMC appreciation, but as a low timer you want to stay good VFR ie minimum risk of inadvertent IMC. Once you get to MSA, it might be prudent to consider quadrantal rules even if you below transition altitude and then it gets really complicated.
MSA is only applicable once you have at least done your IMC appreciation, but as a low timer you want to stay good VFR ie minimum risk of inadvertent IMC. Once you get to MSA, it might be prudent to consider quadrantal rules even if you below transition altitude and then it gets really complicated.
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It would probably do you more good to understand and memorise the law relating to low flying, flying over congested areas and large groups of people. I don't really think that MSA is appropriate for VFR, but the previous items ALWAYS apply, except...
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It is absolutely correct to say that there is no requirement to calculate an MSA for VFR. But it is globally accepted as best practice to do so, both as metric for deteriorating conditions and as significant work load reducer and general life preserver should you find yourself in IMC.
As far as any students reading this are concerned, your examiner will ask you how you calculated your MSA, so don't let individual comments (however potentially valid) persuade you not to bother
Make sure you are familiar will all theSafety Sense leaflets. In relation to this discussion SSL05
As far as any students reading this are concerned, your examiner will ask you how you calculated your MSA, so don't let individual comments (however potentially valid) persuade you not to bother
Make sure you are familiar will all theSafety Sense leaflets. In relation to this discussion SSL05
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When I did my skills test, the examiner did expect me to calculate a saftey altitude. He asked how I calculated it. I havd calculated it just as IO540 described above
The examiner commented that he was delighted, because he wouldn't have found the MEL (from the grid on the chart) +1000 to be acceptable.
dp
I think the answer that is expected from a PPL is that one draws the track line on the chart, and looks 5nm either side of it, take the highest obstacle found, add 1000ft to it, round the answer up to the next 100ft, and that becomes the MSA for that entire leg of the route.
dp