AOPA Pilot Magazine - February 2017 - 82

P&E

82 |

ADS-B

recommendations that air/ground determination be more sophisticated than
simply a groundspeed value. For example,
some Garmin products use a reference
altitude and other data to determine air/
ground status, said Bill Stone, Garmin's
senior business development manager. But
because of a ground station limitation, they
still sometimes get flagged for errors in that
determination.
"What they now call the ADS-B
Performance Monitor doesn't have a lot
of data to work with," Stone explained. It
uses a 25-knot groundspeed value for the
determination, and specifically excludes
rotorcraft. "It seems to be a zero-tolerance
monitor. What's in the aircraft is generally
more robust.
"If you're in your Aeronca Champ on
approach with a 30-knot headwind, you
could be approaching stationary," Stone
said. "There are quite a few challenges
out there."
If the air/ground determination-
or anything else reported by the ADS-B

Performance Monitor-fails 100 percent
of the time, something is wrong, probably with hardware setup or configuration,
Stone explained. But a failure rate of 1 to
2 percent is a nuisance failure, and paying
special attention to the flight profile can
help to avoid them. "If you have a 1 or 2 percent failure rate-and that's where most of
these air/ground failures are-[the FAA's]
offering to process them manually."
Stone related the story of a Piper
Cherokee's owner who failed the air/
ground portion of the test three times at one
airport in the southeastern United States-
and when he flew a test flight at another
airport, the airplane passed on the first try.
"The FAA understands and appreciates the
challenges, and is considering making some
changes to the monitor," Stone said.
To minimize the chances of nuisance
failures, he suggests the following steps.
"Probably the overarching thing is to take
your time," Stone added.
1. Move the aircraft clear of any hangars
or other obstructions before starting, so it

has a clear view of the GPS satellite constellation. Starting between hangar rows
can complicate satellite acquisition.
2. Wait at least two minutes after powering up the avionics before moving
the aircraft, to assure that the GPS has
acquired enough satellites.
3. Taxi slowly to the runway (the "brisk
walk" from our student pilot manuals).
4. Take off, climb, and perform some normal maneuvers-not abruptly, just nice
and easy. (Do not perform aerobatics on
a validation flight. Yes, it's been tried.)
If you are also seeking to qualify for the
rebate, make sure you fly for more than
30 minutes in FAR 91.225 rule airspace,
where ADS-B will be required in 2020.
5. After a normal pattern and landing,
come to a complete stop on the runway.
Then, taxi slowly to the ramp or your hangar and shut down.
Stone said his team is seeing improvements in ADS-B validation testing, and
he believes that pilot patience has been
a big help.

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Copyright 2016 Aspen Avionics Inc. "Aspen Avionics," "Evolution Flight Display System," "Connected Panel," and the Aspen Avionics
aircraft logo are trademarks of Aspen Avionics Inc. All rights reserved. U.S. Patent No. 8,085,168, and additional patents pending.

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Table of Contents for the Digital Edition of AOPA Pilot Magazine - February 2017