When my Cessna taildragger was built
the VOR was still on the drawing board.
The military’s TACAN stations with associated DME had yet to be deployed. Inertial
navigation was a mere dream, and some
were figuring out how to use Doppler techniques to measure drift angle on long-range
over-water flights. In 1945 the four-course
range and fan markers were still the staple
for IFR navigation.
Now VOR/DME is scheduled to be
phased out, expensive inertial nav systems are supplemental, fan markers have
all but disappeared, and Doppler preceded Loran A and C into history’s
dustbin. Even ILS installations are
headed for the chopping block, but the
ADF and NDB live on. Why?
ADF FOR WORLD TRAVEL
The interesting, even surprising, fact
about ADF receivers is that few new
piston airplanes have them, but virtually
all new jets do. The reason for that lies
beyond the borders of the United States.
Most other countries still require ADF
receivers for IFR flying, so turbine airplanes with their longer range and typical
international operations have ADFs while
piston airplanes intended for domestic
U.S. flight usually don’t.
Here in the U.S. the GPS navigators
have eliminated the need for an ADF
receiver. There may still be an NDB
instrument approach that does not have a
GPS “overlay,” but that won’t be true
much longer. The FAA is creating new
GPS approaches by the hundreds, and the
easiest approaches to create are when
there is already an approach to a runway
because the terrain and other necessary
course and altitude clearance survey data
If you have WAAS (wide area augmentation system) GPS navigators,
you don’t even need VOR/ILS receivers
to fly IFR because the FAA has approved
a WAAS navigator as primary. With
WAAS even your IFR alternate
airport—if one is required based on
weather forecasts—only needs to have
a GPS approach.
THE POLITICS OF GPS
So why are we dragging around ADF
receivers to fly in the rest of the world?
After all, the “G” in GPS stands for global,
and the system works just as well in any
country outside the U.S. as it does here. The
primary reason that ADFs and NDBs live on
is political, not technological.
GPS is a creation of the U.S. military
under the control of the Air Force. The
original name of the system was Navstar,
and from the outset it was designed as a
global weapon. GPS cannot, of course,
directly damage an enemy, but it makes it
possible to guide an aircraft, missile, drone,
ship, vehicle, and even an infantryman with
incredible precision. The Air Force did not
originally intend for civilians to use GPS
and certainly never wanted pilots to rely on
it. The FAA obliged and ignored GPS for
many years while it threw money into MLS
(microwave landing system) and expanded
Loran C coverage.
The interesting, even
surprising, fact about ADF
receivers is that few new
piston airplanes have them,
but virtually all new jets do.
But the GPS signal was there for anyone
to receive. The Air Force threatened to turn
the signal off at any time without warning
for security reasons. The Air Force also had
what it called SA for selective availability.
The military intentionally degraded the
accuracy of the “free” GPS signal by randomly “dithering,” as they called it, the
signal. Only military GPS receivers with the
secret codes could get the SA with its accuracy we now all use.
Despite the Air Force warnings entrepreneurs designed, built, and sold GPS
receivers to the public. There had been
nothing like GPS before that could pinpoint your location anywhere in the world,
guide you to any destination, and show
your track and velocity along the way. The