Avionics News July 2013 - 33

Garmin’s GTS 800 is an active traffic system
with optional ADS-B capability, suitable for
use in piston aircraft.

TCAS has spawned both higherand lower-end versions, and
with the advent of automatic
dependant surveillance-broadcast (ADS-B) technology,
onboard traffic systems are
evolving to deliver new capabilities. For this article, I interviewed
representatives from several manufacturers to
provide practical advice to avionics shops on what
systems to recommend, what should be considered in the
quote process and what technicians need to take into account during onboard traffic awareness/collision avoidance system installation and troubleshooting.
Some notes on terminology: All of the systems considered here are active, meaning they involve interrogation
of other aircraft, either using a transponder or ADS-B
transmitter. While passive systems exist, today they
are all non-technical standard order portable units that
will usually be installed by a pilot without help from an
avionics shop. Having flown with several such systems
in light general aviation aircraft, passive, portable traffic
devices have severe limitations – short range and shadowing by the aircraft structure mean that pilots using
these devices can’t count on them to alert for all threats.
Most portables don’t provide bearing information, so the
pilot can’t even tell what direction to look.
This leaves us with TSO’d active systems, and there
is a distinction between traffic awareness systems and

Honeywell’s
TPA-100 is a
TCAS processor that
requires transponderbased input for collision
avoidance and also accepts ADS-B input for
improved situational awareness.

ADS-B, which offer
a display providing
the pilot with situational
awareness, and TCAS, which
provides traffic alerting for collision
avoidance. There is yet another distinction between the original, Mode C-based
TCAS I and the more-advanced TCAS II. TCAS
II systems exploit the additional data provided by
Mode S to compute relative closure rates and command
a climb or descent to avoid a collision. It’s now required
for U.S. aircraft with more than 30 seats, while TCAS I
is required for aircraft with more than 10 seats.
In addition, several vendors are offering TAS (or
TCAS) in combination with ADS-B. When ADS-B
information is available, it can be used to refine target
location (especially in azimuth), and ADS-B targets can
be detected at greater range. It should be noted, however, that ADS-B can only be used today for situational
awareness. Collision avoidance is still the province of
transponder-based systems.
Now let’s look at what shops and technicians need to
consider before the quote, during the installation and
when troubleshooting becomes necessary.
All of the vendors told us that selecting a system appropriate to the aircraft is critical. Avidyne’s TAS600,
for example, is limited to operations below 18,000 feet;
thus, it is suited only to non-turbocharged piston engine
aircraft. At the other end of the spectrum, RockwellCollins noted that TCAS II systems, whether from them
or competitors, require an aircraft be capable of at least a
1,500 foot per minute change in altitude. While there are
a few passenger aircraft that can’t always climb that fast,
including the fixed-gear, Short 330/360, they are capable
of descending at high rates. But as an engineer told us,
“When an operator inquired about installing TCAS II in
a blimp, we told them no.”
Display compatibility is an issue – while most TCAS
II systems use ARINC 735B, lower-end units may be
proprietary. There also can be compatibility issues with
other pieces of equipment, particularly transponders.
Several manufacturers use approved model list supplemental type certificates to simplify the approval process.
If a particular aircraft isn’t covered, installation may still
Continued on following page
avionics news

•

july

2013

Avionics News July 2013

Table of Contents for the Digital Edition of Avionics News July 2013