Pilot's Guide to Avionics 2015-16 Edition - 69
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.
isn't so equipped, and " all of the sudden, it's a pretty
The unknown on the stand-alone WAAS/GPS-ADS-B
system, said Harpster, was the FAA. " Would it be
comfortable disabling a unit's intended function" and
replacing that capability with a separate stand-alone
unit? Apparently so. Gulfstream just certified the Garmin
solution on its G150 and G200, said Harpster. Another
challenge, he continued, is the system's teething pains.
" The FAA says 20 percent of all ADS-B installs are not
done correctly; when seen on ATC screens, airplanes
are disappearing or jumping to parallel routes 3 to 5
miles away, and then jumping back."
The downside of the stand-alone ADS-B solution,
added Loso, is its WAAS/GPS engine serves only the
transponder. That works for ADS-B, but it does not
open the door to LPV instrument approaches, which are
supplanting the ILS at airports nationwide, and tighter RNP
tolerances, which open the door to optimized flight paths.
If ADS-B is NextGen Phase I, controller-pilot datalink
communication is Phase II, Loso continued. It is a digital
communication through VHF when in line-of-sight range
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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 surveillance-contract) 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
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