Plan-G Questions

[wain 879]

you are quite correct there March, however I wanted to take this route and have a look around the area as I am new flying in that area, didnt want to see just the mountains...

Wayne

[Quickmarch 488]

Trust me, Wayne. I live there. Mountains look only marginally different from the side than they do from the top. If it were me, I'd prefer to be looking down on them. That way when the wx goes sideways, you know where they are and they can't bite. I (we) call them cumulo-granite when viewed from the side.

 

That aside, your scheme of doing an end-run around them works fine. I won't even bring a boat into Tofino from the west (real nasty place and a lee shore) without several backups - the most important is a 180 deg turn.

 

We're quickly getting off-topic. PlanG is a mighty good VFR planner. 

 

PS: I think that there's a bit of mis-direction sent your way with respect to MEF (sorry Brett). The MEF, someone correct me if I'm wrong, is the highest "natural" obstacle within a half degree square on your track. Towers and really tall stuff should be noted on your sectionals.

 

Hah! found it in the PlanG instructions - Quote: MEF (the ninth and last column populated by Plan‐G) stands for the Maximum Elevation Figure, and is the highest point (not including masts, skyscrapers etc.,) in a 0.5o square through which the track passes. UnQuote - see page 64.

[wain 879]

thanks March, the quote is actually on the pages I printed along with the tutorial I printed, but I must have missed that bit.

 

You are correct I think Plan-G is amazing, I use it all the time now if I need a plan...

Wayne

[brett 2,284]

Thanks March for the correction but I got my info from a flight training pdf from the AOPA and I quote a small section;

5. The Maximum Elevation Figure (MEF) represents
the highest elevation, including terrain and other
vertical obstacles (towers, trees, etc.), within a quadrant.
A quadrant on Sectionals is the area bounded by ticked
lines dividing each 30 minutes of latitude and each 30
minutes of longitude. MEF figures are depicted to the
nearest 100' value. The last two digits of the number are
not shown. In this example the MEF represents 12,500'.
MEFs are shown over land masses as well as over open
water areas containing man-made obstacles such as oil
rigs.

 

I know towers and such have their own elevation marking but I am to understand that a maximum number is based on all the elevations within that area, so how do get a definitive answer and would this answer depend on where we live?

[Quickmarch 488]

@ Brett, sorry if I seemed to be criticising your comment. 

 

I was repeating verbatim from the PlanG Manual. As the question relates to PlanG, I thought this info might be the "best fit". As you, and all the rest of us, are aware, the Flight Sim environment doesn't always accurately mirror the RW.

 

(see endless "engineer" jokes elsewhere in this forum)

[wain 879]

I have recently dicided to stop looking at new stuff that can be used in fsx but has different data...because of what March wrote above....

[brett 2,284]

@ Brett, sorry if I seemed to be criticising your comment. 

 

I was repeating verbatim from the PlanG Manual. As the question relates to PlanG, I thought this info might be the "best fit". As you, and all the rest of us, are aware, the Flight Sim environment doesn't always accurately mirror the RW.

 

(see endless "engineer" jokes elsewhere in this forum)

 

March, I would never take anything you say as a criticism, you have always been a gentleman of the highest order (well maybe with a little bit of salty scalawag thrown in ). You were totally correct in your answer to the question as quoted so no apology needed.

 

Let me restate my limited writing skills and try and ask the question, "Why does PlanG use a definition of an aeronautical term that differs from my past understanding of MEF, could it be because Tim decided to encompass differing definitions across world sectional charts."  I don't know.

 

I ask this because I based my response from a US flying school document and from what I generally knew to be the proper understanding of the term. Maybe in Europe they do not include man made items when figuring MEF. Just trying to broaden my horizons.  

 

[Quickmarch 488]

Remember that we are used to North American terminology and (I think) Tim is from the UK. I'd almost bet that the UK version of the term and the N American one differ slightly.

 

Try telling a NA girl that you'll "knock her up in the morning" and see what happens.

[brett 2,284]

Haha, along with a few others that I have been slapped for.

 

You may be right, I will see if I can find something from the UK.

[brett 2,284]

Hmm, it's not in the CAA glossary but I did find something in a CAA SafetySense Leaflet for VFR Flying concerning charts:

d) Identify high ground from the spot
heights and contours and remember
that the highest point en-route is
often the top of an obstruction.
Calculate and note the minimum
altitude you can safely fly each leg.
SSL 5e 3 December 2008
The Maximum Elevation Figures
(MEF) on charts give the elevation of
the highest known (or likely) feature
in each quadrant in hundreds of feet
amsl. These figures provide no safety
margin from the features.
 

I find it odd that MEF was not in the CAA glossary and mentioned in passing in a safety leaflet. I am hoping that a UK pilot or Tim will weigh in, it could be as simple as another term being used in the UK or it was easier to code PlanG with only natural elevations. I did also find something that mentioned obstacles under 299 feet did not count in the equation from the CAA.

 

I don't want to beat a dead horse but I do like to figure some things out.

[Andrew Godden 934]

Brett,

 

This now takes me back to my earliest days as a cartographer and working on aeronautical charts such as the ONC, TPC and JOG(A) series.

 

MEF is an international term and your first definition is the most accurate.  I would debate (and it always has been debated as this was always an issue of contention during production of the charts) whether it takes into account vegetation, as the height of trees varies over time and their height cannot be accurately measured anyway.

 

In flight planning and planning your minimum cruise altitude, the general idea is you find the highest MEF value on your flight path.  To this you add 100ft for vertical error, then the height of the tallest obstacle in the quadrant / quadrangle (terminology varies, but it means the same thing) or 200ft, whichever is the higher, and then round up to the next 100ft.  You then round up to the appropriate flight level according to the bearing of the flight path and the relevant application of the 'Qandrant Rule' (used in the UK) or the 'Semicircular/Hemispheric Rule' (UK for IFR inside controlled airspace and rest of the world generally).

 

Example - For a VFR flight, the flight path is on a bearing of 069 degrees, the highest MEF is 2³ with a 175ft obstacle.

 

Minimum Cruising Altitude = 2300 (MEF) + 100 (vertical error) + 200 (tallest obstacle or 200ft) = 2600ft then rounded up to the next 100ft = 2700ft then apply the 'Semicircular Rule' = 3500ft

 

The same example for an IFR flight would need to take into account the MSA or LSALT, the definition and rules of which vary more widely by country, to produce a minimum cruising altitude.

 

Some might choose to debate the need to round up to the next 100ft in this instance, but it would only be academic anyway by the time you apply the 'Semicircular Rule' and besides, it provides an extra safety margin.

 

Cheers

Andrew

[Quickmarch 488]

I learn something everyday.

 

In Canada, I was taught to add 500 ft to the highest elevation along the flight path (or 1000 ft if the flight direction called for it). I don't recall what we called it in the dim and distant past, but "bugger factor" (sometimes spelled with an F)  comes to mind. This, of course, provided you stayed under 10,000 ft.

 

Thanks for the clarification, Andrew.

[Andrew Godden 934]

I learn something everyday.

 

In Canada, I was taught to add 500 ft to the highest elevation along the flight path (or 1000 ft if the flight direction called for it). I don't recall what we called it in the dim and distant past, but "bugger factor" (sometimes spelled with an F)  comes to mind. This, of course, provided you stayed under 10,000 ft.

 

Thanks for the clarification, Andrew.

 

March,

 

I'm sure slight variations exist from country to country in the way it's taught, particularly with the view to an added safety factor, or a quick, sure way without having to do all the individual additions - just as long as you didn't have an obstacle over 500ft. 

 

You might call my example a "from first principles" calculation, and I know that applying a general rule of 500ft will result in the same answer 99.9% of the time.    I always did like the tedium and ad naseum of "from first principles" though. 

 

Cheers

Andrew

[Tim_A 996]

Within Plan-G, MEF figures only include terrain. Obstacles are not included because that would be dependant on whatever scenery you have installed, and Plan-G has no way to examine all your scenery models and work out their heights. This obviously differs from the real world, where such features are included. (in the UK, the CAA charts only include features 300ft or taller, which is where the "MEF + 300" figure comes from.)

 

 

For comparison, this is the statement on a UK half-mil VFR chart:

MAXIMUM ELEVATION FIGURES (MEF)

Maximum Elevation Figures are shown in quadrangles bounded by graticule lines for every half degree of latitude and longitude. MEFs are represented in thousands and hundreds of feet above mean sea level. Each MEF is based on information available concerning the highest known feature in each quadrangle, including terrain and obstacles and allowing for unknown features. NB THIS IS NOT A SAFETY ALTITUDE.

 

Now, regarding suggested altitudes. This comes from memory, since it's a long time since I looked at it in detail.

 

For VFR flights, Plan-G starts with a base altitude of MEF + 1000 ft. For IFR flight, the base altitude is MEF + 3000. Then 1000 ft is added for every 20 minutes of flight time. This is then rounded up to the next cruise altitude (odd-thousands heading east, even thousands heading west. In some countries (Italy, New Zealand), the rule is applied North-South.  The UK uses a quadrantal rule rather than hemispherical. VFR flight altitudes are only rounded up once they get above 3000ft AGL (above MEF).

BTW, I don't think there's a rule about 1000ft per 20 minutes, it's just a sensible number that gets used a lot round here.

 

Since your flight plan was heading west, my gut feeling is that you should have been offered 10000 ft, or 10500 VFR. I'll have to look into that tonight when I get home.

 

[brett 2,284]

Ok, this explains a lot. I had already read some of what Andrew posted while looking for my quotes but you always explain things so well. So thanks for that.

 

As March simply stated, the original question from Wayne pertains to PlanG and I appreciate Tim's post as well. It explains something that I always wondered when building long flights as to why the MEF can be so high over a relatively low elevation terrain/obstacle situation.

 

I for one love when a thread evolves like this, I just wish I was smart enough to understand it all.

 

To think before this I always thought MEF was simply a figure based on the tallest elevation around the area where shown on the sectional chart for VFR flying and I would add 300'-500' above that for a "safe flying altitude", after all, I can see where I am going. Boy was I wrong.

 

PlanG rocks, thanks Tim.

   

 

 

[wain 879]

thanks to all who posted and thanks to Tim for explaining how it works in PLAN-G, I have learned a fair bit here and now understand why the altitude was given.

 

Agree with Brett to about PLAN-G..

 

Wayne

[Tim_A 996]

Still haven't looked at why the plan gave you the altitude it did - it's over 38 degrees in my "office" (that's 100+F in old money). I'm sure you'll understand if i wait till the weather breaks!

[wain 879]

Yeah I know what you mean with the heat.. just not used to it in Blighty....

I am wondering if it may have something to do with not having a profile set up for the Titan yet...is there like a default if no profile is loaded?

Wayne