Aviation Forum / General / Soaring / September 2008

Last December I reported in this forum that I was starting a project
to extract airspace information from the National Airspace Resource
Files (NASR) published by the National Flight Data Center, and to
translate that information into file formats commonly used in the
sport aviation community (such as OpenAir .txt and Tim Newport-
Peace .sua formats).  I embarked on this effort because of the
withdrawal from publication of the Digital Aviation Flight Information
File (DAFIF), which for years had been the main free source of
airspace data used by US sport aviators.

I am pleased to announce that this project has finally come to
fruition.  I anticipate that there might be some questions about it,
so I am taking the opportunity in advance to answer some of them here.

Question 1:

How does this data compare to translations based on the National
Flight Database (NFD), such as those available by subscription on the
JustSoar website?

Answer:

The arcs and lines that make up airspace boundaries are specified
explicitly in the NFD data.  By contrast, the NASR data comprises only
lists of points along the airspace boundaries.  It is, however,
possible from those lists to compute estimations of actual boundary
positions by fitting arcs and lines to them.  In my translation the
computation is done such that the estimated boundary lies within about
300 ft. (.05 NM) of the points given in the NASR data.  This is the
expected error of the translation process.

The question of the accuracy of the NASR data itself deserves some
comment.  The FAA recently initiated a project to publish and re-
verify airspace data in the NASR using a new file format (GIS
shapefiles).  In July, this project was completed for airspace classes
B, C, and D, and the “not for navigation” designation that had
previously been applied to those shapefiles was removed.

The shapefile project for special use airspace, including Restricted
and Prohibited airspace, Alert Areas, and MOAs, is just getting
started..  SUA data is currently published in the NASR using an older,
much less precise format that has been in use for years.  I have
found, corrected, and reported the most obvious errors in the SUA
data.  Some of these have been as much as a mile or so.

Generally speaking, I think the NASR data compares favorably to the
old DAFIF files, although there may be some exceptions.

Question 2:

Why use the NASR data at all?  Isn’t the NFD data adequate?

Answer:

Unlike the NFD data, the NASR subscription is free of charge, and
comes without a restrictive license agreement.  My translations are
also free of charge, and may be freely copied and redistributed.

Question 3:

Where can I get your translations made from the NASR files?

Answer:

The files for the next charting cycle, effective September 25, are now
available in the Special Use Airspace section of the Worldwide
Turnpoint Exchange.

Lynn Alley
“2KA”

PS for programmers:  I have made the source code for the programs that
produce the NASR translations freely available in a public domain
SourceForge project called “Air2”, in the SVN repository.  You may use
it for any purpose you wish.  Obtaining and installing the required
libraries and languages is fairly involved, and shouldn’t be
undertaken casually.  Expect to spend days.