January-February 2022 - 19

operations - such as emergency rescue and police
aircraft - by interfering with radar altimeters.
During a webinar held the evening of Jan. 13,
HAI's Director of Government Affairs, John Shea;
Seth Frick, radar systems engineer, Honeywell
Aerospace; and Nick Kefalas, a Lockheed Martin
technology fellow at Sikorsky Aircraft Corp.,
addressed the potential disruptions of 5G's rollout.
Frick stated that Honeywell has been conducting
" substantial testing " on all of the altimeters models
they produce to discover what 5G's impact will be.
" The behaviors we observe in the laboratory setting
do vary by model to model. But generally, we've
observed everything you can imagine, " Frick said.
Some of the behaviors recorded have been
altimeters " becoming noisy, " putting out altitude
misreadings of plus or minus 50 to 100 feet. Other
disruptions have been more severe, with altimeters
giving no reading at all or giving erroneous readings
of hundreds and thousands of feet off true altitude.
Compounding the issues, sometimes the altimeters
do not recognize that the information they are displaying
is wrong and provide no warning to pilots.
Frick noted that in real-world scenarios, they
expect things to be more dynamic than can be
represented in the laboratory.
" There's going to be a range of different impacts, "
5G services may result
in the grounding of
emergency rescue
helicopters.
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he continued. " Our conclusion has been, based on our
testing, that there's not really any kind of failure mode
that we could safely rule out. You could have detected
faults, loss of function. You could have undetected
erroneous output, which could constitute hazardously
misleading information depending on how that
altitude output data is used onboard the aircraft. "
There are two primary modes of interference that
are of concern. Frick said they are referred to as front
door and back door coupling. As he explains, 5G
networks put out high-powered signals in their own
frequency band, separate from the altimeter band.
However, the altimeters don't have perfect filtering
for these bands built into them, meaning they pick
up some of the 5G network's signals regardless.
Frick continued that 5G networks will also leak
out much lower levels of interference directly into
the altimeter band. He said that the former, the highpowered
signals, appear right now to be what causes
the most altimeter disruptions.
One solution is to increase an altimeter's filtering.
However, retrofitting altimeters to filter the 5G
signals is a process that can take anywhere from six
months to a year. And not all models will be able to
be retrofitted and will need to be replaced.
In the meantime, the FAA is offering the same guidance
to rotorcraft operators as they are to those of
their fixed-wing brethren - guidance based on protection
zones around 5G towers and airports. These
zones are two nautical miles out from an airport's
runway threshold. If a 5G tower's signal crosses into
these protection zones, a pilot will need an alternative
method of compliance (AMOC) to land.
Yet, this guidance is of little help to heliport operators,
which do not yet have similar guidelines, or
rescue operations that may be flying and landing in
unconventional areas to complete their missions.
" The NOTAMs that were released today cover
both airspace procedure and aerodromes. If you are,
say, in the New York Metropolitan Area where you
have JFK on the south of the island and LaGuardia
on the north, there may be zones within that area
that you may have to drop below certain altitude,
or there will be an altitude of a 'no-go' zone, " said
Kefalas. " We have seen information that shows that
the lower you get, the better your performance is. So,
all that will have to be weighted in the way operations
are conducted going forward. "
Kefalas continued that the situation with the
towers is fluid. As more and more 5G towers come
online, these protection zones will shrink as towers
intrude on them. To help combat this, the FAA is
working on a plan with the Federal Communications
Commission (FCC) to have them deliver a report
every three months of where new towers are being
brought online.
The FAA will use this information, along with the
testing of altimeters, to build a database of where
it is safe for aircraft to operate, depending on the
equipment they have. This process would continue
into the foreseeable future as the 5G network grows.
" That's going to be an ongoing and dynamic process, "
Kefalas said. " They are doing this [5G] rollout
in phases, so every three months, we will be getting
additional towers. So these assessments from the
FAA against these databases will be ongoing, at
least for the foreseeable future until we stabilize
the number of towers popping up, which at some
point, I would expect that the AMOCs to be more
under control and not needing to be coming out at
that frequency. "
Editor's Note: On January 28, the FAA, Verizon and
AT&T reached an agreement to continue the 5G rollout.
Read more at https://www.aviationpros.com/
21254948 and visit AviationPros.com for the latest 5G
developments.
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January-February 2022

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