NAVIGATION
Above: Pressure on aviation’s use of the radio spectrum is growing as mobile broadband suppliers look to increase their services
priority so maybe the use of DME will not be
sustainable over the next couple of decades.”
Pressure also comes from adjacent
frequencies. Wireless company Ligado wants
to place powerful transmitters on the ground
in the US as part of a 5G mobile network
that will supersede LTE networks. Ligado,
formerly named LightSquared before
bankruptcy and reorganization, has not been
able to secure access to these frequencies
from the US Government, but has not given
up trying. Goward and Parkinson are
concerned about possible interference with
GPS signals and receivers if the government
grants permission for adjacent frequency
operations.
Parkinson points out that if an eLoran
system was built and used by civil aviation
then the FAA could retire some of its ground
based navaids. And if the US Government,
not the FAA, builds an eLoran system for
overall GPS backup, most experts believe
civil aviation would probably use it along
with a dozen other industries that depend on
GPS for time synchronization or positioning.
Drones ahead
Airliners are not the only air vehicles
expected to be occupying civil airspace in
the years ahead. Drones and air taxis will
depend a lot on GPS and are unlikely to be
equipped with VOR and DME, according to
Parkinson. Advocates for drone delivery
envision thousands of them flying
simultaneously over large urban areas. Air
taxis may also be hopping autonomously
from one skyscraper helipad to another or
directly to a passenger’s back yard in the
suburb. What if GPS goes out in this
scenario?”
You have the problem of navigation and
control of the air vehicle but the second
problem, which is equivalent and totally
unresolved is the air traffic management for
these things,” says Parkinson. “The key in
both cases is GPS and the pertinent question
is, do you have a backup for it?”
Parkinson believes if the US government
gives the go ahead to build an eLoran system
to act as a backup for the GPS system, a GPS/
eLoran computer chip could be developed
for small drones and autonomous air taxis
that would seamlessly feed eLoran data from
the vehicle for air navigation in case GPS
goes down. “Industry is not even going to try
to develop that unless the government
decides to bathe the critical areas with
eLoran signals,” he says.
44 AIR TRAFFIC TECHNOLOGY INTERNATIONAL 2020
Is eLoran likely?
Parkinson believes building an eLoran
system would cost about as much as one GPS
satellite, around US$300 million and that it
would have cost less if the US Government
had not dismantled the Loran C system.
He also believes that eLoran may be about
to happen finally after 15 years of discussion
because of several political developments.
Goward agrees with him.
In Washington, the National Space-Based
Positioning, Navigation, and Timing (PNT)
Advisory Board, which provides advise on
GPS-related policy, has been recommending
that the US government give the go ahead to
build an eLoran system for several years.
The PNT Board comprises of 25 industry,
academic and international GPS experts,
who advise the US government on GPS
policy and programs. They last met in early
June. Former PNT advisory board member
Scott Pace became the executive secretary of
the National Space Council when it was
revived by the Trump administration in
2017. Diana Furchtgott-Roth, the DOT
Deputy Assistant Secretary for Research and
Technology, also supports a GPS backup.
Several US Senators including Ted Cruz also
back the initiative to build a GPS backup.
“Industry is not even going to try to
develop that unless the government
decides to bathe the critical areas with
eLoran signals” Brad Parkinson