Changes to ChartData Due to Removal of DAFIF
from the Public Domain
For years, the US Department of Defense (DoD) has collected
aviation data from countries all around the world and put it into a massive
aviation database that is updated every 28 days. This database, called DAFIF, is primarily for military use but the DoD also produced a non-classified
public version. Over the years, most aviation software has come to rely on
the public DAFIF data to give pilots the official data we need to fly safely.
In November 2004, the DoD announced that,
starting October 1, 2005, DAFIF would be completely withdrawn from the public
due to intellectual property concerns voiced by a few foreign aviation
authorities . This caused a tremendous outcry from pilots, the aviation
industry and AOPA because some of this data, especially airspace information, is
not available from any other public source. In response, the DoD postponed
the cutoff date until October 1, 2006 and created a special US-only version of
DAFIF, called USFIF, which would be available until October 2007.
Using FAA Data as of October 25, 2007
The FAA is clearly the original source for most
US aviation data so it only makes sense, ultimately, that the FAA provide the
data directly rather than via the DoD. They have been working to fill the
US digital data gap that the withdrawal of DAFIF produced. As of this
writing, the FAA provides virtually all of the data required for aviation but
not quite all of it. In particular, Seattle Avionics relied on the very
detailed airspace data from the DoD to draw airspace. This data contained
a wealth of information beyond simple shapes and altitudes. For example,
it included communication names and frequencies, comments about unusual
situations (like some Class D airspace reverting to Class E when the tower is
closed) and so forth. The FAA has chosen to produce most airspace data in
a format that many commercial drawing programs can digest called Shapefile.
As the name implies, a shapefile is a file that describes a shape such as an
airspace. Oddly, especially given the name, shapefiles describe all shapes
as simple point-to-point line segments. The DAFIF data, by contrast, was
richer in that it described complete shapes as series of line-line segments but
also as circles and arcs (think about most Class B, C and D airspace).
While the FAA system of using a large number of points to approximate a circle,
rather than just saying something like "5 NM circle at -119.5w / 49n" works, it
uses more data space so our data files are larger. More importantly, the
FAA data is lacking a number of crucial bits of inflight information such as
contact names and frequencies. Finally, and most troubling, the FAA
shapefile data mentions upper and lower altitudes without reference to whether
the altitudes are MSL or AGL. In most cases, the altitudes are clearly one
or the other so our data processing attempts to interpret the altitude correctly
but there will be many cases where we won't "guess" correctly.
We mentioned that the FAA is using shapefiles
for most airspace. They have stated that they will eventually use
shapefiles for all airspace, but they currently produce shapefiles for just
Class B, C, D and E airspace. They do not produce shapefiles for Class A
or any SUA. This means that we have no current source of Class A airspace
but we do have SUA data because they publish the SUA data in an entirely
different format elsewhere. We process the SUA data from this second
source and merge it with the shapefiles for the primary airspace to produce a
seamless data set. This SUA data is much more complete than what we get
with the shapefiles; it mentions altitudes as AGL or MSL (usually!), includes
contact information, etc.
We have been in contact with the FAA about
these problems and they recognize the issues and are working on solutions but
have no timeframe. In the meantime, please be aware that we are
doing the best we possibly can with incomplete data.
Canadian and Mexican Data
Prior to the DAFIF cutoff on October 1, 2006,
the Department of Defense provided us with current Canadian and Mexican data.
Since that time, we don't have current data but have provided Canadian and
Mexican data that was valid as of that date. As time continues, this data
becomes less and less reliable. Therefore, we plan to drop the old
Canadian and Mexican data entirely from the standard Voyager data set
sometime in 2008.
We clearly recognize the value of this non-US
data, not only for Canadian and Mexican pilots, but also for US pilots who fly
north or south of the border. In keeping, we opened communications with
Nav Canada. In 2006, we visited Nav Canada in Ottawa to try to obtain
information comparable to what was available from the FAA. At the time, we
learned that, unlike the FAA, which is a government agency with a primary
mission to promote aviation safety, Nav Canada is now a privately held company
with profit as a main motivation (conceptually similar to the US Post Office).
During the meeting, Nav Canada told us that some data would be available at some
point and that we should contact them again in a few months. Indeed, since
that time, they have sent us sample data and we are soon to look at what
processing the data entails. We do not know how much Nav Canada will
charge for the data but we have reason to believe it will be in the hundreds of
dollars per pilot per year. When we have reached an agreement with Nav
Canada and have worked out the technical details, we'll make an announcement.
We have not made any provisions to get current
What This Means To You
If you are a US pilot who flies only within the
50 states, Puerto Rico, and the US Virgin Islands. you should not notice any
major difference, in the long run, but should not be surprised to see some data
difference and/or errors for a few data cycles until the FAA fixes the new
If you are a Canadian pilot or a US pilot who visits Canada,
neither Seattle Avionics nor most other aviation companies can provide you with
until Nav Canada provides it to us.