Minimum Safe Altitude

[night hawk 150]

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

[scubawasp]

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.

[Mariner9]

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 :ok:

[High Wing Drifter]

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'.

[IO540]

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).

[Mariner9]

IO's right, but I seem to recall for the nav written examsyou have to remember the additional 300' uncharted obstacle clearance

[FlyingForFun]

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
---------------

[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]

[night hawk 150]

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

[DRJAD]

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?

[EGTC]

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.

[High Wing Drifter]

EGTC,
I usually just use the MEF + 1000, unless I need to fly lower than this to get under controlled airspace
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 :uhoh:

[IO540]

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.

[windy1]

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.

[EGTC]

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.

[High Wing Drifter]

EGTC,
Fair enough old chap. I think I somehow managed to read your view as meaning you wanted to stay above MSA at all times :=

[Whopity]

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!

[Droopystop]

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.

[Piltdown Man]

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...

[High Wing Drifter]

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 :ok:

Make sure you are familiar will all theSafety Sense (http://www.caa.co.uk/application.aspx?categoryid=33&pagetype=65&applicationid=11&mode=list&type=sercat&id=21) leaflets. In relation to this discussion SSL05 (http://www.caa.co.uk/application.aspx?categoryid=33&pagetype=65&applicationid=11&mode=detail&id=1159)

[dublinpilot]

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

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.

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

[Pronto]

Just one thing to add. I was taught the same method as Dublinpilot (but using 10 nm either side of track, not 5). I saw mention a few years ago that when calculating MSA in mountainous areas, you should use the highest elevation within 10 nm of your track plus at least 2,000 feet.

I appreciate that this is entirely irrelevant over the Suffolk alps, but for those venturing into Wales, Cumbria or the Highlands it may be very relevant.

P

[slim_slag]

People appear to be mixing MEA (Minimum Enroute Altitude) up with MSA (meaning Minimum Safe Altitude, not Minimum Sector Altitude).

Minimum Safe Altitude, relating to VFR, is something like

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:

(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.

(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.

(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

Minimum Enroute Altitude, which is includes the concept of a 'designated mountainous area' is an IFR thing, but one should certainly have this calculation in mind when flying VFR X-country, maybe flying at or above this altitude would mean you were obeying (a) above, and you would impress an examiner with your airmanship. I also thought mountainous areas were a bit higher than found in the UK, if talking about flying over them.

[bookworm]

People appear to be mixing MEA (Minimum Enroute Altitude) up with MSA (meaning Minimum Safe Altitude, not Minimum Sector Altitude).

I think that's because the US has a rather more rigorous set of definitions for minimum altitudes, with MEAs, MRAs, MOCAs, MORAs etc. The "1000 ft above the highest obstacle within 5 nm" that comes from the UK's Rule 29 doesn't really have an equivalent label.

[slim_slag]

bookworm, Student~C150~Ipswich is a student pilot, we are talking VFR here.

[bookworm]

Student~C150~Ipswich is a student pilot, we are talking VFR here

and he also seems to be based in the UK, so is likely to need to know the UK situation, not the US rule that you quote.

The point is that there's a difference in the labelling: 91.119, which you quote (and incidentally applies to both VFR and IFR), has an equivalent in the UK, Rule 5. But the altitudes described in Rule 5 are not termed Minimum Safe Altitudes in the legislation, and are not usually referred to as such by UK pilots.

Thus in the UK, Minimum Safe Altitude is open to interpretation -- it's not something that can be "mixed up".

[slim_slag]

Well spotted bookworm! I did indeed quote from a FAR. As you correctly point out, "Minimum Safe Altitude" is not defined in the UK for VFR flight, and is open to interpretation. In these cases I find it useful to see how others do it, and hopefully the interpretation I posted is something like what Student~C150~Ipswich is looking for to answer his question - which was what is 'Minimum Safe Altitude'

Rule 29 which you cited is not really open to intepretation, it clearly doesn't apply to VFR flight. In my opinion it is there purely there to guarantee some degree of obstacle clearence when you are in the clouds. When VFR cross country your obstacle clearance is assured by visual means. Sometimes I have been VFR 100ft AGL in designated mountainous areas (real ones) and felt very 'safe'. Other times I've been 5000ft AGL and having to constantly search for places to land, and these have been few and far between.

Talking of learning from others. The UK has a 'glide clear' regulation which doesn't exist in the FAA rulebook. It would be churlish of me to say 'this UK rule doesn't apply to me' when I am flying above US cities. Knowing the 'UK situation' makes me a safer pilot, I believe.

[bookworm]

Rule 29 which you cited is not really open to intepretation, it clearly doesn't apply to VFR flight.

I agree, though it is Rule 29 minimum altitudes that UK pilots regularly refer to as "MSA". You also make a good point regarding the difference between legal minima and the practical interpretation of safe.

[Whopity]

The attached paragraph comes from the CAA Chief Flight Examiner and was promulgated to the Industry in Training Com 1/2004
http://www.caa.co.uk/docs/33/1_2004.PDF

1. VFR OPERATION AT MINIMUM LEVEL
When teaching Navigation, it is reasonable to teach students to plan a minimum altitude for each VFR leg that ensures compliance with Rule 5 (Rules of the Air Regulations 1996) and NOTAMS; if the cloud base lowers forcing the pilot to descend from his cruising level towards this planned minimum altitude in order to remain in VMC, he now has a yardstick to help him decide when to turn back. If the weather appears to be deteriorating further he should turn away (early) because on his plan, further descent on this track is unlikely to be an option. The problem is that FIs are calling this minimum altitude “MSA” or “Safety Altitude”. This is not acceptable; MSA and Safety Altitude are IFR safety minima. It is essential that FIs teach the correct meaning of these terms, how they are calculated, and avoid confusion with any VFR minimum altitude.

[High Wing Drifter]

Whopity,
The problem is that FIs are calling this minimum altitude “MSA” or “Safety Altitude”. This is not acceptable
Cast your eye up to my post referencing Safety Sense 5 and have a read. This just goes to show that the CAA is populated by a bunch of people with much opinions and little correlation of terminology.

FWIW and personally, I don't think it pays to be overly retentive about the use of the wording MSA. It is clear, it says what it is and people know what it means. Getting caught up in purely symantec difficulties is just confusing everybody.

[BigEndBob]

Perhaps Caa should create a new term " Minimum cruise altitude".

I always taught 10nm either side of track, highest hill plus 300 feet, plus 500 feet or highest structure above that, plus 500 feet to determine a minimum exceptable cruise altitude should the cloud base drop. Also use this as a go/no go on cloud base forecast.

Draw three parallel lines onto a sheet of acetate, each 10nm apart and use as a overlay when flight planning.

Using the MEF can also be a bit restrictive should there be a high obstruction in the "corner of the box".