Avionics News April 2018 - 48

PASSING THE TEST

Continued from page 47

antenna from the aircraft's nose. And does the aircraft
have a squat switch? To make sure everyone is on the
same page, Hill said DMFS works with a standardized
configuration sheet.
Aircraft owners can contribute to the problem when
they acquire a new N-number, according to Hill. If the
owner does not have an avionics tech program update
the flight ID and ICAO address, the chances that the
aircraft will not make it through the filter increases,
which negates the value of an ADS-B investment.
In the ADS-B filter's Federal Register notice, the
FAA said three years of ADS-B monitoring revealed a
number of aircraft with nonperforming equipment, and
their transmission of bad data to ATC and other ADS-Bequipped aircraft make them a potential safety hazard.
In addition to incorrect ICAO addresses and flight
IDs, bad data includes unassigned/invalid ICAO
addresses. The FAA said at least once a day, the system
identifies an aircraft transmitting an ICAO code that
should never be used, "000000" or "FFFFFF."
In "Getting it Right: What you need to know about
ADS-B installation errors," a March/April 2017 Safety
Briefing article, the FAA said roughly one-in-five
ADS-B Out installs suffer from performance and/or data
problems, most of them GA aircraft. Other installation
issues included missing barometric pressure altitude;
missing Mode 3/A code; the wrong emitter category;
and aircraft position errors.
"In the grand scheme of things, most GA airplanes I
see pass," Hill said. "I do see a few that don't, usually
because of their emitter category (which denotes aircraft
size based on weight). More often than not, it is the
heavy iron that has issues. They have complied with the
ADS-B puzzle, but they have some wrong pieces."
When connected to a GDL 39R portable ADS-B
receiver, an iPad with a Pilot app lets Garmin dealers
look at all the ADS-B categories, Hill added. He uses it
to scan every aircraft that comes into the shop. Looking
at two aircraft then flying over Des Moines, he said a
UPS airplane, descending from 34,675 feet at 523 knots,
was not Mode 3A compliant, "but that's the only thing
he's missing in his data set."
According to its emitter code, the other was a small
48

avionics news

april

2018

(15,500 to 75,000 pounds) aircraft at 41,000 feet. "Its
MOPS (operating software) is not compliant; it's the old
Version 1 instead of Version 2. Mach velocity has failed;
estimated position error has failed; it's not outputting
latitude and longitude; and he's not transmitting his
Mode A code, which is a requirement. This guy is not
compliant," Hill said. "He's gonna get filtered."
The parameters that integrate the equipment that make
up an ADS-B system are vastly different, Hill noted.
They vary by aircraft type, Part 23, Part 25, amateurbuilt experimental, and rotorcraft, and they depend
on the equipment involved, 1090 ES, a Universal
Access Transceiver, or both. Considered a dual system,
technicians must program each of them with the same
ICAO address and flight ID to avoid another ADS-B
error.
Configuring an ADS-B system to the aircraft it
represents is standard, Hill said. Like anything that
involves a computer, it's garbage in, garbage out.
Accuracy begins by sourcing the necessary information
from the FAA aircraft registry and the appropriate
documents provided by the avionics manufacturer, and
the aircraft's approved flight manual.
Checks and balances are essential. After installation,
an FAA ADS-B Focus Team installation policy memo
says an ADS-B Out system must verify that it complies
with both the system configuration and equipment
performance requirements of 14 CFR 91.227. This
includes a number of programming parameters,
including the aircraft-specific ICAO code address,
emitter category and various components of navigational
accuracy.
The memo gives avionics repair stations two
acceptable methods of verifying compliance. The first is
Ramp Test Equipment, which reads and displays all the
ADS-B parameters. The FAA "strongly encourages" that
technicians connect ground test equipment directly to
the ADS-B system being tested (or use the appropriate
antenna coupling/shielding equipment) "to preclude
signal propagation into local airspace."
An Operational Flight (Evaluation) and PAPR request
is the other accepted method. A PAPR has two sections.
The Operation Summary gives the reported and assigned
ICAO code, N-number, when the flight started, ended,
its duration, and the percentage of that time the aircraft
was a TIS-B client.

Table of Contents for the Digital Edition of Avionics News April 2018