By Adam Hunt
The VHF-AM radios that we all use in our aircraft have remained pretty much
unchanged since the late 1940s, but it looks like change is coming, mandated by
the FAA south of the border.
The major reason for changing VHF-AM aeronautical radios is frequency
congestion. When VHF was first introduced into aviation use there were 90
channels available at 100 KHz separation. Splitting the frequencies and
extending the band allotted to aviation took that number to 360 channels at 50
kHz spacing by the 1960s and then 720 channels at 25 kHz spacing in the 1970s.
Finally in the 1980s a few more frequencies were added at the top of the band
bringing the number available to the current 760 channels at 25 kHz spacing. The
problem is that in many places, especially in the U.S. and Europe, there is a
shortage of frequencies available to handle the need.
The U.S. uses more than 10,000 frequencies for ATC alone and that means that
many frequencies are shared. Due to VHF-AM’s limited range, stations far apart
can use the same frequency without interfering, but as the need has grown it has
become impossible to prevent interference. There just aren’t enough frequencies
to go around.
The European solution has been to slice the frequencies once again and create
three channels where there were one – going to 8.33 kHz spacing and creating
2,280 possible channels. The experience has been mixed with such tight spacing
as some adjacent frequencies overlap and interfere with close frequencies,
mostly due to the limitations of the radio transmitters used.
The FAA has recently made the decision to go a different route under a project
name of Nexcom (Next Generation Communications). This solution will leave the
spacing at 25 kHz but switch from analog to digital radio and include a data
link capability. Under Nexcom, being tested right now in the U.S., four digital
channels share each frequency at a spacing of 25 kHz. The result, in theory,
should be clearer communication with less interference, better security and a
total of 3,040 possible channels available.
The downside is that digital radios only work with other digital radios and that
means that all the existing radios will all be obsolete eventually.
The FAA has not proposed a hard implementation date for switching, but instead
plans to bring about a gradual changeover starting in 2009 to be complete
sometime after 2015. It is very likely that those dates will slip, too, as they
usually do in projects of this size and scope.
The FAA plan includes introducing the digital air-to-ground service in the
high-level airspace (above 18,000 feet) first and then gradually introduce it to
lower altitudes. That means high-flying aircraft will need both old and new
radios for a while during the change-over.
The FAA also plans to equip their ground stations with new dual digital/analog
radios during the transition so that analog radio-equipped aircraft will still
be able to talk to terminal, ground, FSS and tower, at least until the end of
the transition period.
To ensure that the new radios are available the FAA has been funding radio
development projects by radio manufacturers Avidyne, Collins and Honeywell.
Testing of the first units was carried out in Florida in 2003 with voice and
data link. The main small aircraft radio manufacturer of the three, Avidyne,
expects to have their first digital radio available commercially by the summer
of 2004.
The FAA intends to introduce changes to the FARs in 2005 to start to bring in
the new digital radios by the planned program commencement date of 2009.
So why should Canadian pilots who don’t fly to the U.S. care about this? The
main reason is that our radio system will be changing too, like it or not. One
factor is that U.S. aircraft will soon be equipped with only the new digital
radios and will not be able to communicate with our aircraft or ground stations
if we don’t switch. The second factor is that once the U.S. starts switching,
the radio manufacturers, located predominantly in the U.S. and Japan, will stop
making the old analog radios. So, we have no choice in adopting the new U.S.
standard.
Nav Canada is already well along in the planning process to switch over to new
radios. Their new generation of radios is already on order and will be
introduced over the next eight years. These new multi-function radios will work
with both the current analog radio system, both 8.33 and 25 kHz spacing and
Nexcom digital and will be adaptable for VHF digital link, covering all the
proposed combinations in both the European and FAA plans.
Transport Canada is also involved in planning for the changeover to the new
digital radios and is regularly communicating with the FAA on its plans. Even
though the FAA is committed to the Nexcom project at this point there are still
many technical and political hurdles to overcome before the first systems are
used operationally.
Transport Canada have indicated that there have been interference issues on
installations on large transport aircraft and that installations on some light
aircraft types may be very difficult. There are many other technical issues that
may yet result in large-scale changes to the proposed radios and how they work.
There are political hurdles as well. Despite the fact that the FAA is committed
to Nexcom at this point some airline associations, along with many U.S. airlines
are opposed to the adoption of the system. European opposition is expected as
well, since they are committed to a different system at 8.33 KHz spacing.
ICAO has not yet considered the implications of changing the world’s
aeronautical radio system and that body may yet make totally different
recommendations to nations about the world standard for aeronautical
communications.
There are also hurdles to be overcome if digital radio is to be introduced in
Canada. One of these is that aircraft with digital radios and aircraft with
analog radios will not be able to talk to each other.
The incompatibilities between the digital and analog radios may be partly
mitigated by the Nav Canada plan to have all their ground stations (tower,
ground, ATIS, terminal, centre, FSS, etc) dual-equipped, but that means that at
Canadian uncontrolled aerodromes there may be aircraft on the same frequency
that can’t talk to each other.
The clear solution is that there will have to be a “hard change-over date” when
the MF and ATF frequencies across the country will be designated “digital” and
anyone who still has the old radios will be NORDO. All indications are that that
date will be well into the future. TC officials have indicated that they don’t
expect a mandatory changeover in Canada until at least 2024, so our current
analog radios should be good for some time.
Regional aviation agreements between the U.S. and Canada will require the FAA to
provide services to Canadian aircraft in analog radio format until Canada has
completed a changeover to digital radio, too. That should keep Canadians from
being shut out of the U.S. airspace, should the U.S. changeover ahead of Canada.
COPA will be monitoring the developments in digital VHF-AM aeronautical radio
and Nexcom and will keep COPA members informed as the situation progresses.