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ADS-B is a major step in the direction of free flight.
While ADS-B shows great promise for both air-to-air
and air-to-ground surveillance, current aircraft transponders will continue to support surveillance operations in
the NAS for the foreseeable future. If enough users
equip with ADS-B avionics, the FAA will install a
compatible ADS ground system to provide more accurate surveillance information to ATC compared to
radar-based surveillance.
In the United States, two different data links have been
adopted for use with ADS-B: 1090 MHz Extended
Squitter (1090 ES) and the Universal Access Transceiver
(UAT). The 1090 ES link is intended for aircraft that primarily operate at FL180 and above, whereas the UAT
link is intended for use by aircraft that primarily operate
at 18,000 feet and below. From a pilot's standpoint, the
two links operate similarly and both support ADS-B and
TIS-B. The UAT link additionally supports Flight
Information Service-Broadcast (FIS-B) at any altitude
when within ground based transmitter (GBT) coverage.
FIS-B is the weather information component, and
provides displays of graphical and textual weather
information. Areas of approved use for the UAT
include the United States (including oceanic airspace
where air traffic services are provided), Guam, Puerto
Rico, American Samoa, and the U.S. Virgin Islands.
The UAT is approved for both air and airport surface
use. ADS-B broadcast over the 1090 MHz data link
has been approved for global use.
REDUCING VERTICAL SEPARATION
Current vertical separation minima (2,000 feet) were
created more than 40 years ago when altimeters were
not very accurate above FL 290. With better flight and
navigation instruments, vertical separation has been
safely reduced to 1,000 feet in most parts of the world,
except Africa and China.
RVSM airspace has already been implemented over the
Atlantic and Pacific Oceans, South China Sea, Australia,
Europe, the Middle East and Asia south of the
Himalayas. Domestic RVSM (DRVSM) in the United
States was implemented in January 2005 when FL 300,
320, 340, 360, 380, and 400 were added to the existing
structure. To fly at any of the flight levels from FL 290
to FL 410, aircraft and operator must be RVSMapproved. [Figure 6-10]
REDUCING HORIZONTAL SEPARATION
The current oceanic air traffic control system uses filed
flight plans and position reports to track an aircraft’s
progress and ensure separation. Pilots send position
reports by high frequency (HF) radio through a private
radio service that then relays the messages to the air traffic control system. Position reports are made at intervals
of approximately one hour. HF radio communication is
subject to interference and disruption. Further delay is
added as radio operators relay messages between pilots
and controllers. These deficiencies in communications
and surveillance have necessitated larger horizontal separation minimums when flying over the ocean out of
radar range.
As a result of improved navigational capabilities made
possible by technologies such as GPS and CPDLC, both
lateral and longitudinal oceanic horizontal separation
standards are being reduced. Oceanic lateral separation
standards were reduced from 100 to 50 NM in the
Northern and Central Pacific regions in 1998 and in the
Central East Pacific in 2000. The FAA plans to extend
the 50 NM separation standard to the South Pacific.
Because flight times along the South Pacific routes often
exceed 15 hours, the fuel and time savings resulting
from more airplanes flying closer to the ideal wind route
in this region are expected to be substantial. Separation
standards of 30 NM are already undergoing operational
trials in parts of South Pacific airspace for properly
authorized airplanes and operators.
DIRECT ROUTING
Based on preliminary evaluations, FAA research has evidenced tremendous potential for the airlines to benefit
from expected routing initiatives. Specifically, direct
routing or “Free Flight” is the most promising for reducing total flight time and distance as well as minimizing
congestion on heavily traveled airways. Traditionally,
6-11
pilots fly fixed routes that often are less direct due to
their dependence on ground-based NAVAIDs. Through
Free Flight, the FAA hopes to increase the capacity, efficiency, and safety of the NAS to meet growing demand
as well as enhance the controller’s productivity. The aviation industry, particularly the airlines, is seeking to
shorten flight times and reduce fuel consumption.
According to the FAA’s preliminary estimates, the benefits to the flying public and the aviation industry could
　
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