Avionics News March 2017 - 21
for a decline in general aviation accidents. Much more
data dispute this contention. Aviation safety authorities
and aviation veterans note the difference between
causation versus correlation. Yes, you can correlate a
decline in general aviation accidents with the iPad era
- but the correlation lacks a causation link necessary to
close that circle.
The rate of general aviation accidents was already
declining - and continues to, in general. But counter to
the popular belief, iPads and other portable and installed
digital devices too often contribute to problems in the
In fact, as you can see in the sidebar, increases in
incidents stemming from cockpit distractions not only
correlates with the iPad era, but investigations provide
the causation link absent from claims of safety gains.
And used without the full understanding of its
limitations can expose an aviator to risks of not seeing
traffic or properly identifying threatening weather - two
of the benefits of equipping with ADS-B In, permanently
mounted and portable alike.
One example rests with the type of ADS-B In
Not one see-all solution
Most stand-alone In systems use receivers tuned for
978 MHz for the Traffic Information Service-Broadcast.
Originally, TIS-B service, derived from transponder
replies to ATC radar, was programmed to see only
"client" aircraft - that is, aircraft equipped with approved
ADS-B Out and ADS-B In. Aircraft carrying ADS-B In
equipment receive data directly from nearby aircraft with
ADS-B Out on the appropriate frequency (1090 MHz
or 978 MHz). Those using only ADS-B In equipment
often received incidental TIS-B information, resulting
in a traffic picture that would not show all the traffic -
because TIS-B information was optimized for a different
"client." The traffic picture, circular in shape, was not
programmed to be seen by ADS-B In-only systems.
Early last year, the FAA started changing TIS-B to
ensure all aircraft using certified ADS-B In systems "see"
But for portable-system users, the choice of an ADS-B
In receiver that sees only one of the two frequencies -
1090 MHz is the other frequency - may not directly see
traffic broadcasting ADS-B Out on 978 MHz. So some In
systems seeing only 1090 MHz won't always detect and
display 978 MHz aircraft, and vice versa.
A system that receives both 978 MHz and 1090 MHz
assures reception from both types of systems. Why two?
When working on the basics of the ADS-B
components, the FAA decided that 978 MHz systems
could be produced less expensively than the Mode
S/1090 MHz Extended Squitter transponders being
adopted in all other countries; so the FAA created a
second option. The Universal Access Transceiver - that
sends and receives ADS-B on 978 MHz - is an option for
aircraft that never fly above Flight Level 180, or 18,000
feet mean sea level, the start of Class A airspace.
The 1090 ES option can be used at all altitudes - and,
as noted, is the standard adopted by all other countries
adopting ADS-B for their traffic-surveillance needs. And
it sees traffic from other 1090 ES Out-equipped aircraft,
as well as traffic relayed from ground stations.
But it's important to note that there can be some
difference between the location of traffic as shown on a
display and its actual position, due to latency in the relay
The weather conundrum:
What you see is not what's there
Weather datalink. Radar images, live - in the cockpit.
Increasingly, that presence stems from the use of a portable
ADS-B In receiver using 978 MHz, with other datalink
options accounting for the balance. FIS-B is not available
via 1090 ES transponders the way TIS-B traffic is.
And it's difficult to question FIS-B's value as a
strategic tool for cross-country flying.
Unlike onboard weather radar, weather datalink lets
pilots see whatever amount of continent they wish - from
zoomed in on the 100 miles ahead or pulled back to see
several states ... even the entire continent.
Also, unlike onboard weather radar, what pilots see
from weather datalink radar images isn't live or real
time. That's why weather datalink providers all warn
against trying to use those radar images for real-time
weather avoidance, services ranging from the FAA's
Flight Information System-Broadcast (delivered via
ADS-B In) or one of the other commercial services. As
the FAA notes, FIS-B is strictly an advisory service and
not a substitute for standard weather briefings or preflight
weather planning. Similarly, the agency notes FIS-B is no
substitute for official weather sources such as air traffic
control, flight service stations, NOAA or DUATS.
The collection and delivery technologies enjoyed some
improvements in recent years, but none good enough to
replace the real-time live images of onboard weather radar.
The technology itself is at the root of those warnings.
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