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Obstacle Data - Frequently Asked Questions

Terms - Words and Phrases We Use

Does a structure's AGL (height Above Ground Level) include anything on top of that structure?
Yes. Always include the tallest structure/appurtenance (i.e. antenna, light, lightning rod for towers; penthouse, helipad, flagpole, electrical/air conditioning equipment, etc. for buildings) on top of a structure when determining the AGL.

What is the difference between the Weekly Construction Notice and the Daily DOF Change File?
The Weekly Construction Notices and the Daily DOF Change Files do show the same change information for the 56-day DOF and the Daily DOF respectively, but they are in different formats and on different schedules because they are used by different users.

Do Added files always refer to new construction?
Not always. Added files could be either newly constructed obstacles or existing obstacles that were not previously in our database.

Power lines are categorized as Catenaries and the data for these objects contains a single coordinate. How should we figure out the path of the power lines based on that data?
The catenary is the highest point in the sag above ground between transmission towers. No directional data is included. You would have to identify the related transmission towers in the Digital Obstacle File (DOF) to determine the direction. You could also check the related Sectional Aeronautical Chart to see if the transmission lines are plotted.

Products - Digital and Physical Products

Why is the Daily Change File (zipped or unzipped) blank on Monday mornings?
The Daily Change File is blank on Monday mornings because there are no changes to the DOF on weekends or holidays. We are currently working on adding a message to the file to explain this, which we hope will help avoid confusion/frustration.

Do you have data for Restricted Operating Zones (ROZs)?
We do not maintain ROZ data.

Do you have a catalog or other distribution list of Sectional Charts?
For information on Sectional Charts and other FAA products, please review the items in the Aeronautical Information Services Products Catalog.

Is it possible to obtain your data as an Excel or .csv file?
No, it is only available as a text file at this time.

Procedures - How We Do Our Job

Why don't you remove a structure from your database when the OE/AAA case has been terminated?
When an OE/AAA case is terminated, the associated structure is not necessarily dismantled. A termination means that a planned project/scenario (i.e. height change, frequency change, new construction, dismantlement, etc.) has been cancelled.

Why is this structure listed in your database when it was dismantled ten years ago?
Dismantled structures (denoted as "D" in our database) are kept as historical records. However, if a dismantled structure was not reported, it remains as "Constructed" (or "C") in our database.

Are Dismantled and Removed obstacles removed from the 56-day DOF or the Daily DOF?
Both of these statuses are included on the 56-day Change File (CHG.dat) and the Daily DOF Change Files. "Dismantled" files are kept in the DOF and the DDOF for historical purposes, while "Removed" files are removed from both.

Why does the Quantity field sometimes show a number larger than "1" (more than one obstacle)? Does this mean the file includes multiple points?
The number in that column is normally "1" unless there are obstacles grouped very close together. In the past, they were treated as "arrays" and there could be anywhere from 2-9 obstacles in an array. The coordinates for an array were the center point of the grouped obstacles. We no longer enter obstacles as "arrays," but there are still some in the database. As we evaluate these, we will break them up into individual obstacles with their own Lat/Long, AGL and AMSL. We only put "single point" features in our database. At this time, we don't have the capability to input linear features or polygons.

When during the construction process is a structure added to the DOF?
When the aeronautical study is received from the Obstacle Evaluation Group as a new structure Under Construction or Completed to its greatest height, our analysts will verify the data. Upon verification the case will be assigned a file number (ORS identifier), forwarded to a Quality Control Specialist for review, and entered in to the ORS/DOF database. The DOF is refreshed every day at 11:46pm for all approved data files that were entered for that day.


Where would I find standard FAA obstruction symbols?
All of FAA's obstruction symbol explanations are in the Aeronautical Chart User's Guide, which is available as a large (23 MB) downloadable PDF file.

Does the JDATE in the DOF reference the number of elapsed days since the beginning of the 4-digit year (ex. 2012145 = 145th day since the start of the 2012 year)?
Yes. To convert to and from Jdates, try this Julian Date Calculator.

Can you advise your customers of important changes by email?
For any significant changes, please subscribe to the Safety Alerts and Charting Notices webpage.

If you have specific questions, please see Aeronautical Inquiries.

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