I was examining FAA's legacy files, which contain information for various airspace elements, and I noticed that there is a field in the airport layout file called "Controlling Object", for both base and reciprocal ends of the runway.

Some of its properties:

  • Controlling object description
  • Controlling object marked/lighted
  • FAA CFR Part 77 runway category
  • Controlling obstacle clearance slope
  • Controlling object height above runway
  • Controlling object distance from runway end
  • Controlling object centerline offset.

It seems that it's an obstacle near the airport, but I can not tell why it is more important than the others. Does it lead to the most adverse situation, as far as aircraft's climb gradient is concerned? Does also the term "Controlling Obstacle" exist?

Could someone point me in the right direction?


'Controlling object' is, as far as I can tell, the old term for 'controlling obstacle'.

From the TERPS manual (Appendix B):

Controlling Obstacle. The obstacle on which the design of a procedure or establishment of a minimum altitude or angle is based on. See also Order 8260.19, Flight Procedures and Airspace.

Controlling object is mentioned as a field in the Public Use Airport Runways database:

Attribute_Label: BE_CTL_OBJ
Description of the controlling object at the base end of the runway
(e.g., trees, bldg, fence, none).
Attribute_Definition_Source: FAA

And as you can see, it can be trees, a building, and so on.

  • 2
    $\begingroup$ I believe that it’s actually the most critical obstacle, i.e. the one that drives climb gradients or minima etc. as high as they are. Your TERPS excerpt kind of confirms that it’s the critical one („The obstacle on which [...] is based on.“). $\endgroup$ – Cpt Reynolds Jun 20 '19 at 7:57
  • $\begingroup$ Thank you this was really helpful, however could you clarify, if it's something you have knowledge of, how many controlling obstacles the design of a procedure has to take into consideration? I am asking because from TERPS it seems like there is one controlling obstacle (near the airport), but on the other hand Obstacle Clearance Areas are designed for each leg separately, at least in recent PBN manuals such as 8260.58A, which means that it would stand to reason to have as many controlling obstacles as the legs of the procedure. $\endgroup$ – Vector Zita Jun 20 '19 at 15:31
  • $\begingroup$ @VectorZita: I don't know, but I'll try and look into it. $\endgroup$ – ymb1 Jun 20 '19 at 21:18
  • $\begingroup$ @ymb1 Thank you, I really appreciate the effort. I believe it is very important to be clarified how many controlling obstacles exist per flight procedure (one near the airport, one for each leg etc.). $\endgroup$ – Vector Zita Jun 24 '19 at 13:38
  • $\begingroup$ @VectorZita: Check page 2-35 of 8260.19H (PDF page 69). I'm still not 100% sure, but based on paragraphs c. and d. (before 2-11-5), for RNP it is per-leg/segment basis, for non-RNP multiple controlling obstacles are evaluated and based on that the most applicable is used. $\endgroup$ – ymb1 Jun 24 '19 at 15:37

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