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in order to focus on just one, to be taken
forward as the new global standard.
Navigation
Navigation, almost as old as communication,
has developed from simple
Non Directional Beacons (NDBs) and
Direction Finding (DF) equipment to VHF
Omnidirectional Ranging (VOR) with DME
to provide guidance to pilots along air
routes and provide positioning data to
support Area Navigation Capability. For
landing, ILS has been the guidance aid
used to enable low visibility procedures
down to Cat III over the past 50 years.
With the advent of Global Navigation by
Satellite Systems (GNSS) initiated by the
USA Global Positioning System (GPS),
we now have the ability with a single navigation
source of operating globally to an
accuracy of a few metres. This source,
aided by space-based augmentations,
provides accuracy and availability capable
of supporting approach down to Cat I,
and with GPS augmented by Ground-
Based Augmentation (GBAS) it is capable
of supporting low-visibility procedures.
Focus
10
Global CNS
The cornerstone of the next
generation抯 ATM infrastructure
Central to all future navigation applications
is the use of an on-board Area
Navigation RNAV system. The need to
ensure the compatibility of the airborne
system requirements has led to the
coordinated development of initial RNAV
standards with compatible JAA and
FAA specifications. More recently this
has led to the joint development of the
Performance Based Navigation (PBN)
concept under the auspices of ICAO.
Whilst the PBN concept has been
designed around existing standards, it
is now turning its attention to the need
for new standards for RNAV system
capability to support the longer-term 4D
RNAV or business trajectories as they
are known in SESAR. Although a full
4D system with negotiated contracts
as identified in SESAR and Next Gen
are still some way off, it is not desirable
(nor practicable) to maintain Precision
RNAV for what could be in excess of 15
years without gaining benefit from some
simpler initial steps to enable support to
continuous decent approaches and also
to make use of the required time of arrival
capability. As a result, EUROCONTROL
and FAA are working to support the ICAO
RNPSORSG3 activities indentifying an
interim capability, aimed at providing this
step towards the full SESAR/NextGen
capability in the 2015-17 (i.e. IP2) period.
Surveillance
Finally surveillance, the new kid on the
block, only introduced around 1945,
is used to allow controllers to 搒ee?
the aircraft and ensure that they are
flying where they should. The most
basic surveillance is called Primary
Radar, where large pulses of energy are
bounced off the aircraft抯 fuselage, the
reflections are detected and the position
plotted. Modern systems use a transponder
which is located in the aircraft.
Secondary Surveillance Radar (SSR) uses
such a transponder to connect to information
sources on the aircraft to provide
altitude and identity information. SSR
Mode S, the latest SSR development,
also allows the provision of other parameters,
including aircraft identity (e.g. AFR
106) and selected altitude, a very useful
parameter to avoid safety issues caused
by level busts.
Automatic Dependent Surveillance ?
Broadcast (ADS-B) is a recent surveillance
development. This differs from SSR
radars in that the aircraft determines its
own position and transmits that position
to the ground and to other aircraft. The
position, based on GPS, is transmitted as
latitude and longitude enabling a display
of traffic to the air traffic controllers on the
ground and to pilots in other aircraft, if
fitted with suitable ADS-B equipment.
The ADS-B Air Ground Surveillance application
standards are being produced
through the Requirements Focus Group
(RFG), comprising EUROCONTROL, FAA,
EUROCAE4, RTCA5, Australia, Canada
and Japan. This international collaborative
effort is working extremely well. The
RFG is also working on the air-air applications
for airborne situational awareness,
spacing and separation. These
applications are key to the success of
SESAR and NextGen and hence need
to continue to be developed in the same
spirit of international cooperation and
dedication.
Finally multilateration (MLAT), used at
airports and Wide Area Multilateration
(WAM), used in en-route and TMAs to
compute the position of the aircraft using
data from a number of separate, omnidirectional
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Skyway Magazine Autumn 2008(6)
