Avionics News February 2017 - 46

GHOSTS IN THE MACHINES
The Federal Aviation Administration recognized a problem with ADS-B In
back in 2013 and moved to resolve the issue. With the availability of nonTSO'd ADS-B Out products, some pilots opted to buy in as a way to increase
their visibility to other aircraft through ADS-B In systems.
The problem: FAA systems didn't recognize or "see" the output from
these ADS-B Out broadcasts due to differences in their digital coding.
In other words, those nonapproved ADS-B Out transmissions - labeled
nonperforming emitters or NPEs - were effectively invisible to other aircraft
and ADS-B ground stations. If controllers could see them at all, it was
because of their Mode C or Mode S transponder squawks.
The FAA decided to modify the TIS-B Target Status logic in its software
to uplink TIS-B messages for ADS-B NPE aircraft with the process due to be
finished in 2016 after rolling out the changes in late 2015. The FAA gave
manufacturers a year to modify their systems to prevent ghosting of some
NPE targets for uncertified ADS-B-In systems.
To get the most out of ADS-B In, the aircraft needs to squawk with an
approved ADS-B Out system of some form. q

REGULATORY LIMITATIONS OF ADS-B IN SERVICES
Aircraft owners should be made to understand the limitations the FAA set
for ADS-B In as a stand-alone function - and the FAA's reminder that both FIS-B
and TIS-B are "advisory only" services. That means a traffic target showing on
TIS-B is not an authorization to deviate from ATC instructions or otherwise act
in violation of the Federal Aviation Regulations. It is a good reminder to talk to
ATC about the observed traffic and ask permission to deviate.
TIS-B is not - repeat not - equivalent to TCAS ... the Traffic Alert and Collision
Avoidance System specifically designed and approved to direct pilots away from
a possible in-flight collision.
So, TIS-B advisories - available on some systems and with some applications
- are just that: advisories. Old-fashioned see-and-avoid still prevails.
Maneuvering to avoid an unseen TIS-B target could result in an airspace
infraction or a separation-standard violation. But avoiding what a pilot sees and
believes is an imminent collision remains the smart move in the minds of most
pilots - and in that regard, the pilot-in-command is always right.
The FAA feels the same about FIS-B. Deviating, without ATC permission, may
help a pilot avoid unwelcome weather and still land the pilot in hot water if
that heading change results in a violation.
Systems that are approved for avoiding weather and traffic remain available
- and standard equipment on many higher-end general aviation aircraft. And
they still cost more than the hull value of many general aviation aircraft.
The FIS-B and TIS-B services available from ADS-B In remain advisory only.
But in the end, it's for the pilot-in-command to decide to make a radio call
and then whether risking a violation by making a heading or altitude change is
a smarter option than a possible conflict. q

avionics news

february

2017

ADS-B IN

Continued from page 45

FIS-B, however, is continuously
broadcast and, for the majority of
pilots, available sitting on the ground.
TIS-B data is transmitted from a
ground station and can be received
on both ADS-B frequencies - 1090
MHz ES or 978 MHz, with the 978
MHz participants rebroadcast on
1090 MHz. The traffic information is
taken from ADS-B Out signals and
radar sensors on ground stations, then
rebroadcast through ADS-B In for
use by equipped aircraft; In-equipped
aircraft can see Out-equipped aircraft
directly, if within the coverage range
of the In receiver.
So, to be clear, it's possible to
have an ADS-B In receiver and see
no traffic because no ADS-B Out
aircraft are operating in the ground
station's service area.
So what do ADS-B In aircraft
get to see? Other traffic, thanks
to TIS-B. And, through FIS-B, a
host of weather and safety of flight
information. These items from
FIS-B come in various forms, some
graphic, some textual, all useful.
Now, 1090 ES ADS-B Out
solutions generally can't receive FIS-B
services because FIS-B is broadcast
on 978 MHz used by universal access
transceivers. But some 1090 ES
ADS-B Out solutions include the
ability to receive 978 MHz to give the
customer access to the FIS-B services.
And what are the FIS-B services?
Rather extensive, actually. FIS-B
currently offers:
* Aviation weather products
such as METARs, TAFs,
winds aloft and NEXRAD
precipitation maps, in both
text and graphics forms.
* Temporary flight restrictions
and status updates for special
use airspace.

Table of Contents for the Digital Edition of Avionics News February 2017