Airport Design Editor HelpArticlesWhy are there are Trees on My Runway!

Why are there are Trees on My Runway!

Many airports are out of date or not very well represented.  It is common for folks to want to enhance their local airport.  It is also common that in doing so trees and buildings end up on the new aprons, taxiways and runways.   Sometimes the new areas of the airport are either above or below ground as well. This tutorial looks at the reasons for this and also how to deal with it.  

Note that this tutorial is applicable to FSX and P3D.  Different techniques are needed for FS9.

Getting Started

We are going to use KHUT - Hutchinson Municipal Airport  -  in this tutorial  



Take a careful look at the light brown area (1)   This is called the airport background.  All airports are going to have one of some size or another and cover the effective area of the airport.  Airports in FSX are flat.  It the real world there is pretty much no such thing as a flat airport since they all have to live in the surrounding landscape and truly flattening such a large ares would be impossible and not necessary.  Runways at real world airports will have slopes and even humps and hollows.  This is not the way it is in the  simulator however. The light brown area is called the Airport Background Polygon and it is probably the most important terrain element that you will need.  Things are a bit different in FS9 and that version of the simulator is not covered here.



Airport Background Polys are not created using the same XML source code and compiler as the airport itself.  While we can extract the airport information out of a Bgl file we can't do the same thing for terrain elements and that includes the Airport Background Poly (ABP).  So the stock ABP is not going to appear when we open a stock airport.  There is generally a good way to work out where it is though.  If the airport has a boundary fence (1) then that is most likely to follow the edge of the ABP.  Looks pretty similar doesn't it?

If there is no airport fence or you want to confirm the location of the ABP then you can connect ADE to FSX and move the user aircraft around the ABP in FSX and mark it out in ADE.

Map Out Background Poly via Flight Simulator

First connect ADE to your flight simulator.  Check out this article  if you need to brush up on how to do this

In the simulator slew the user aircraft to a corner or point on the background poly - use the arrow keys to slew

Lock ADE to FS.

Lock ADE to FS.

Click the Lock Button.  This will make sure that the aircraft symbol stays in the center of the ADE display and does not get lost out of view.

Add a Marker

Add a Marker

In ADE select the marker tool

Move the marker cursor over the center of the user aircraft

Left click to add the marker

Repeat this until you have marked out the background poly

Repeat this until you have marked out the background poly

Chances are that your markers will line up accurately with the airport fence.  So if there is a fence then you can safely use that as the boundary of the stock ABP

Save your airport project before going any further

Removing the stock airport background poly

Generally if we are going to work outside the existing area of the airport background poly then we will need a new one and it is probably better to first exclude the stock one.  

Select the Terrain Poly Tool

Now create a small poly - a rough rectangle will do - but make sure it cuts the boundary of the airport background poly

  1. Select Exclude General for the Type
  2. Select Airport Backgrounds for the Tag
  3. Click OK to save the information

Compile the Airport

Make sure that the simulator is not running and compile the airport

Then start the simulator and go the the airport

Oops - buildings and trees all over the airport.  So now we know that the airport background poly is what keeps all the autogen away from the airport

Add back the Airport Background Polygon

Add back the Airport Background Polygon
  1. Select the Terrain Polygon tool
  2. add vertexes for each corner point of the boundary fence or for each marker you added to show the boundary - remember to double click the last point to close the poly
  3. Set the Type to Airport Background
  4. Set the Tag to Flatten Mask Class Map ExcludeAutogen
  5. Save it by clicking OK
  6. Save your work
  7. Compile the airport and open it again in the flight simulator

NOTE:  Make sure the leave the exclusion you made earlier in place to ensure the default ABP is not displayed

The Airport Background Poly is back - the important thing is that this is the one we added and not the stock one so it can be extended or changed to include any new features we want to put outside the stock boundary

Adding new features

I am now going to add some new features outside the existing boundary.  I will add a new apron and some taxiways but we could extend a runway or move one or some existing feature

A simple apron and hangar outside the boundary fence.  And like all good new construction sites the fence (1) stops folks getting in!

Save and compile the airport again (make sure the sim is not running) and then check out how it looks in the simulator

Here is our new facility but it is covered in buildings and some trees here and there.We also need to do something about that fence as well!

Extend the Airport Background Polygon  and move the fence

Extend the Airport Background Polygon  and move the fence
  1. The extended airport background poly
  2. The new fence

Adding or deleting vertexes to an existing vertex based object

Modifying boundary fences and polygon edges will almost certainly need some more vertexes.

Highlight the fence or polygon boundary and move the cursor until the tool tip appears  Ctrl + Left Click will add a new vertex that can now be dragged as desired.  If you want to delete a vertex then select it and hit Delete.  ADE will heal the line.

When you have finished your modifications in ADE:  Save and compile the airport.  Open it again in the flight simulator

And now we can see that the new area has a proper background, there are no trees or buildings in the way and the fence goes around it


In FSX and P3D it is the Airport Background  Polygon that flattens the area and removes and autogen buildings and trees.  We can't load the stock ABP into ADE but it is easy enough to work out where it is and exclude it.  We can then add a new APB and extend it to cover any new features that are outside the stock ABP.



Fine tutor, it is very clear. Thanks a lot.


I have an airport CYBW that has increased the length of one the runways. I increased the length, renamed them to account for magnetic variation and updated all the approaches. But now I can't seem to get rid of the trees that are auto generating on final approach. I have tried following the enclosed instructions without any luck. I know it has to be something I am doing wrong but can't figure out what it is......When I try to remove the stock airport background poly it doesn't work. Nothing changes after I compile. I only have one CYBW file in my addon scenery. I'll add an item to the ADE forum with the file. Not sure what to try next....any suggestions are appreciated.

Kenneth Park

The changes made to my airport area in this easy to follow tutorial could almost be called magical. Before, extended runways and other improvements to the real airport, made it impossible to work with ... this feature not only fixed that but opened the airport up to the addition of major scenery etc extensions.
Simply great programming.

Jon Masterson

You are welcome


Thank you so much for this tutorial. Ive been looking for this for a while.

Jon Masterson

You are welcome


I used this feature to remove trees that were growing in the runway of an airport in a 3rd party scenery scenery package.

I also used ADE to add a couple FSX default log piles and logging truck to the side of the runway…the trees had to have gone somewhere. ;)

Jon Masterson

Thanks Will :)

Daniel Rodriguez

so I cant get the "Tag" and "Type" options in the polygon tool , any help ? and : how do you add a fence ? im doing this cuz the SB0B airport is default and badly done in fs9

Joe Lintzenich

Jon: Great tool. I am a pilot with some computer skills. Could you help? All of the things about the airport polygon work, but at VHHH the airport is surrounded by water. On the north it is a large body and even though I get rid of the stock polygon and draw a new airport polygon to extend to the north where a new runway is going, it seems that the water takes precedence and I only see the part of my polygon that doesn't overlay the water. On the south the water does the same thing but beyond the river the airport polygon can be seen. Don't really need the polygon on the south, only did it to see if I was in fact compiling the new polygon, which it appears that I was. Can you suggest a fix?

Thanks Joe

Jon Masterson

I am pleased that you are enjoying ADE. Terrain Polys are not really my area of expertise. Can I suggest you ask on the support forum at Folks there have a lot more knowledge than me


Thanks alot
It really helped

Harry Karmel

This tutorial really helped, but I have one question. I have just the a scenery for LPPD- Ponta delgada, the azores portugal. I have used the exclusion rectangle to flatten and exclude other unwanted autogen. But being on a island, which is a volcano the a large terrain changes. Therefore in between taxiways there are huge "lumps", as if the taxiway has been dug through the terrain, which of course, is not the case in real life. I have tried isolating these hills with their own rectangle, but it has not worked. Any ideas?
Thanks a lot
Harry Karmel

Jon Masterson


This sounds like an elevation problem. However the best place to get help will be on the Airport Design Editor support forum at Someone there will be able to help


Jean-Pierre Fillion

Hi Jon,

Trees suddenly appears on my airport (CYRJ Roberval).

I am sure that they where not there before.

I dont remember have add a scenery recently.

The scenery is above all sceneries.

I try this page receipe but trees still remains.

You have other clues for me?



Jon Masterson

I think you should ask this on the support forum at It will be easier to resolve there


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