Avionics News April 2015 - 29

Images courtesy of Universal Avionics

The primary components of a future air navigation system are a data-capable cockpit voice recorder, a WAAS/
S-BAS GPS-driven flight management system like Universal's UNS-1Ew, and a communication management
unit like Universal Avionics' UniLink, which routes messages between the FMS keypad and the transmission
system - VHF, satcom or HF - appropriate to the aircraft equipment and location.

nication through VHF when in line-of-sight range of terrestrial
stations and satellite systems, such as Inmarsat or Iridium, when
they are out of VHF range, which is why CPDLC is an integral
part of FANS, or the future air navigation system.
Developed by the International Civil Aviation Organization
in partnership with leading airframe and avionics OEMs in the
1980s, the final datalink plan published in 1993. With no radar
coverage on the trans-Atlantic run, position reports (and the
bubble of safe airspace that surrounded them) determined how
many flights could make the trip. Offering more reliable communications than HF voice, CPDLC conveys position reports as
text messages, and ADS-C (automatic dependent surveillancecontract) makes the datalink reports automatically.
Assessing the wind and weather, every 12 hours the organized
track system determines the roughly half-dozen routes between
Flight Level 350 and 390 that provide the optimum flight and
fuel efficiency. Before CPDLC, these tracks could handle approximately 900 flights a day. Reliable datalink position reports
allowed ATC to shrink the protective airspace bubble, making
room for 500 or so flights each day.
CPDLC is on the NextGen to-do list, but the FAA hasn't yet
published its timeline, said Harpster, but the European Aviation
Safety Agency and ICAO have a number of them. In Europe, the
VHF datalink system is called Datalink 2000+. It is the primary
link in the Single European Sky rule adopted in 2009. There has
been a datalink exemption for some aircraft, he explained, but
operators still need CPDLC to get across the North Atlantic.
As of February 2015, aircraft will need FANS, with 4 nautical
mile RNP, to access any North Atlantic OTS route, and the two

center routes, the most desirable, will have half-tracks. Aircraft
not equipped to FANS standards can still fly outside the OTS
routes - until 2017, when it will be required for all aircraft in
the North Atlantic between FL350 and FL390. In 2020, when the
FAA's ADS-B mandate arrives, all aircraft flying the North Atlantic at or above FL290 must be FANS equipped.
With the increasingly global reach of business jets, FANS is a
growing consideration for operators who cross any ocean. If the
aircraft does not have a satcom system, operators much choose
between Inmarsat and Iridium, according to Harpster. The former
employs geosynchronous satellites whose reach reliably extends
to the 70th parallel, the latter provides global coverage with a
constellation of low-Earth orbit satellites. Like Iridium's satellite
phones, the aviation system is lightweight and small.
Some FANS solutions use a single WAAS/GPS source. "But it
is in the operator's best interest to understand the downfall of such
systems," Harpster said. If the nav goes in-op over the Atlantic, the
aircraft is no longer FANS capable. "It must get out of the OTS
airspace" and fly a parallel path 10 nautical miles away.
Pilots whose single-source nav failed would report their predicament and need to move over with a "free text" CPDLC message.
For nearly all of their routine ATC communications, the pilots
would select the one needed from the menu, according to Carey
Miller, manager of business development for Universal Avionics
Systems Corp. This delivers clear, concise communication that
eliminates one message stepping on another and the ambiguity that
can arise from language barriers or competing accents.
Continued on following page
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Avionics News April 2015

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