Pilot's Guide to Avionics 2013-2014 - 62

ADS-B CIRCA 2013

Continued from page 61

“As it’s been, I could never seem to scrape together
the $6,000 or $7,000 cost of installing one of the better
CAS systems. But, I can afford a 1090ES solution and
a stand-alone 978 receiver to work with the display in
my all-in-one box.”
As for the cost of the second box? Well, he’s getting
a nice trade-in value from his old datalink receiver that’s
largely offsetting the cost of the 1090ES transponder
and installation and connecting it to his WAAS GPS for
position source.
“The 978 receiver is inexpensive enough that it will
be covered by about 18 months of savings from the
subscription service I’m cancelling.”
He could be a poster pilot for the FAA’s entire philosophy of a two-tiered ADS-B solution.
With tomorrow’s transponders becoming available
today, ADS-B gaining traction – both Out and In – let’s
look at the developments in the technology.
There are shortcomings, though. For example, if no
ADS-B Out aircraft are in range of a ground station,
a nearby aircraft with ADS-B In only may not see any
traffic, since ground stations work on-demand – such
as when an ADS-B-participating aircraft is in range to
wake up the station.

ISSUE TWO:
CONFUSION ABOUT THE OPTIONS
Then, there’s deciding what form of ADS-B Out solution to pick. Some solutions have the vulnerability of being
brought down with a critical single-failure-point.
Owners must understand that ADS-B Out works through
three components under the 1090ES option: a TSO-145approved position source – WAAS GPS is the most popular – a TSO-C166b-approved Mode S transponder using
the 1090 MHz frequency spectrum of transponders and
with extended squitter and a TSO-C10b-approved altitude
source, either a stand-alone encoder or one integral to the
transponder, as we’re seeing more of today.
Now, let the encoder fail. Such a failure could leave an
aircraft grounded and its people stranded because the aircraft is unable to enter controlled airspace – ADS-B won’t
be getting an altitude squawk.
Similarly, let the position source or the 1090ES transponder fail and you’re out; or the mere loss of the extended squitter due to antenna or cabling problems lock
you out of airspace where ADS-B Out is required.
All-in-one solutions like Garmin’s GDL90 978UAT
and those from NavWorx take a simpler approach to the
components-based approach, with the Out transmitter
and position source and altitude source all integral to the
same box.

Loss of the box’s functions similarly impacts your airspace access. But with only one component, many avionics technicians believe the chances of losing one of three
components are higher than the chances of losing the entire 978UAT.
Of course, another option exists – using a 978 transmitter, separate 978 receiver, separate position source and
separate encoder. But the more-economical, more-affordable-for-most-pilots choice will be the UAT and its related
antenna.

ISSUE THREE: THE TRANSPONDER:
IS ONE STILL NEEDED POST ADS-B OUT?
One other frustrating complication stares at operators who need to replace a transponder: what to install?
A transponder remains a requirement; the 1090ES
ADS-B Out solution covers that requirement – but not
the other, 978 UAT.
Why does the FAA want people to continue using and
buying transponders?
A regular flying companion of mine owns a businessturbine aircraft and has zero interest in 978 – or a 1090
Mode S transponder that can receive traffic.
Unfortunately for the rest of aviation, the collisionavoidance system of thousands of aircraft need transponder squawk to work with the TCAS system, the
CAS system, and be seen by some radar outside their
control.
For aircraft owners unlikely to invest in ADS-B In, a
1090ES Mode S transponder can underpin the solution
and simultaneously satisfy the FAA’s requirement to
keep a functioning Mode C transponder in the aircraft.
While it can’t deliver the FIS-B benefits of ADS-B In
and 978 UAT, it can provide a traffic input to work with
collision-avoidance systems.
Some CAS systems can receive the ADS-B In TIS-B
info, adding depth to traffic-avoidance capabilities.
Avidyne’s Series 600 CAS systems can deliver the
traffic datalink of FIS-B; the company’s new AXP340
1090ES transponder can serve as the Out link for ADSB and fulfill the FAA’s transponder requirement.
ADS-B In support allows properly equipped Series
600 TAS to receive ADS-B information from 1090ESequipped ADS-B Out aircraft, as well as display traffic
information from in-range Mode A, C and S transponders. The range for receiving ADS-B information is
larger than can be used for active traffic interrogations,
increasing the effective range of the TAS for ADS-B In.
The ADS-B position also will be used to enhance the
accuracy of the bearing and range to a target.
The Avidyne Series 600 TAS also receives the ADSB Out traffic’s data strip – heading, navigation track,
Continued on page 64…

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Pilot's Guide to Avionics 2013-2014

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