Welcome Guest. Sign in or Signup

3 Answers

Controlling obstruction

Asked by: 4095 views
General Aviation

What is a controlling obstruction? It's mentioned in the AFD. I did try to find it in the FAR AIM but no luck! Is it measured from MSL or AGL.?

3 Answers



  1. John D Collins on Aug 29, 2014

    In the context of the AFD, it is a word such as Trees or Tower. It is an indication of what obstacles or terrain feature are of note. I am sure there is a specific criteria, but I don’t know it offhand. IFR departure procedures provide more detailed information such as the distance from the departure threshold, height above ground, and distance off the runway centerline.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  2. Russ Roslewski on Sep 02, 2014

    Controlling obstruction, in the IFR approach and departure world, is quite simply the obstruction that results in the highest minimum descent altitude, decision altitude, or (for departures) the highest required climb rate or ceiling/visibility.

    Think of it this way – you’re coming in to land at an airport, and there is a 50-ft tree at 1/4 mile final. You notice there is also a 40-ft tree at 1/2 mile final. That 40-ft tree is pretty much irrelevant – it’s the 50-ft tree you need to worry about, if you make it over the 50-ft tree you will of necessity have made it over the 40-ft tree. Same theory for departures – a lower obstacle that is farther away is less of a concern.

    But it’s not always just the taller obstacle. For departures, clearly a 50-ft tree 1/4 mile from the departure end of the runway is a concern, whereas a 200-ft tree 3 miles from the departure end is not.

    In the A/FD, it will simply say something like “tree”, with no height data. If you want or need more specific information, you’ll need to refer to the instrument departure for that airport, which will list any pertinent obstructions.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  3. psequeira on Sep 12, 2014

    Thank you John and Russ

    0 Votes Thumb up 0 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.