PHOTOGRAPHS BY LANNON HARLEY
FLYING OPERATIONS
How far can GPS go?
Pilots will be able to use satellite technology instead of traditional distance
measuring equipment (DME) when new rules come into effect in November.
Brad van Wely
HE AIRSERVICES’ SIGNS mounted
on fences near Canberra Airport warn
passers-by to be on the look out for
the endangered species of legless lizards that
make their home beneath the aerodrome’s
navigational facilities.
While the future of the lizard is still uncertain, much of the aging technology now
used for navigation by pilots is destined to
become extinct in favour of the Global
Navigational Satellite System (GNSS).
Australia has been a world leader in the
T
use of GNSS and first approved the use of
the Global Positioning System (GPS) for
instrument flight rules (IFR) en-route navigation in 1994.
A number of GNSS approvals, including
GPS non-precision approaches, have
followed since, and two more are about to
be released. From 28 November this year,
Australian IFR and night visual flight rules
pilots will be able to obtain additional operational flexibility from GPS.
The latest rule changes have been made
possible following the US Government’s
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decision to discontinue selective availability
in GPS from May 2000. This essentially
means that errors of up to 100m deliberately programmed into the technology for
defence reasons by the US military are no
no longer present.
Many of the first generation Technical
Standard Order-C129 GPS receivers were
“hard-wired”to assume selective availability
was on. However, later models, and those
built to the new TSO-C145/146 standards,
can now accurately plot position to within
the wingspan of the aircraft.
FLYING OPERATIONS
Navaids (clockwise from top): Dual GPS units, NDB facility, VOR facility, GPS at work in the cockpit
From a financial standpoint, the latest IFR
GPS receiver now costs about the same as a
new IFR ADF (automatic direction finder).
That trend is set to be maintained, as the
competitive GPS receiver market continues
to drive down the price of the IFR standard
equipment, while the demand for ADF is
now largely limited to Australia, Africa and
parts of Asia, meaning lower production
and higher unit costs.
The end result will be a positive one for
operators who will be able to purchase GPS
receivers for much less than today’s price tag
of about $7,000. This saving is likely to sway
many operators towards the new technology as the combined costs of buying
DME (distance measuring equipment) and
ADF components could turn out to be
much higher in coming years than
switching to GPS.
When changes to the Aeronautical Information Publication (AIP) come into effect
from this November, Australian IFR pilots
whose equipment meets TSO-C129 standards or the equivalent will be able to use
their GPS instead of DME for standard
instrument departures, standard arrival
routes and designated instrument
approaches.
New approach: Airservices Australia has
begun the task of progressively updating
instrument approach landing charts to
show which procedures are suitable for GPS
instead of DME, including details of the
appropriate GPS reference point.
As with the introduction of any new rules,
pilots planning to use these new approvals
should review the requirements carefully
and contact CASA or their flight training
organisation if they are in doubt.
IFR benefits to be gained from GPS in lieu
of DME approvals will include the ability to
fly precision approaches to some of the
instrument landing system runways not
supported by marker beacons, and many of
the runway-aligned “/DME” approaches.
Runway-aligned approaches often have a
lower minimum descent altitude than a
circling approach to the same aerodrome,
providing significant operational benefits
under the new rules.
The aerodrome at Albury on the
NSW/Victoria border is just one of many
where pilots will notice a dramatic difference to the applicable approach minima. At
present, there is a VOR (very high frequency
omnidirectional range) only approach and
two VOR/DME approaches. The VOR
approach has a minima some 850ft higher
than the runway 25 VOR/DME straight-in
approach but aircraft not fitted with DME
are not presently able to conduct the
runway-aligned approaches.
When the cloud is low, pilots of aircraft
without a serviceable DME (and all pilots
when the DME ground equipment is not
FLIGHT SAFETY AUSTRALIA, SEPTEMBER-OCTOBER 2002 < 33
FLYING OPERATIONS
operational) have less likelihood of
becoming visual below the cloudbase.
Once the Albury IAL charts have been reissued, the option to use GPS instead of
DME on the runway-aligned approaches
will be available.
Dividends: The single biggest benefit from
the new rules will be safety related. The
avoidance of circling approaches is
expected to reduce the amount of highworkload flying at low altitude often associated with controlled flight into terrain
(CFIT).
CFIT is singled out annually by both the
International Civil Aviation Organization
(ICAO) and the International Air Transport Association (IATA) as the single
biggest cause of aviation accidents around
the world. In its ongoing studies into the
problem, IATA estimates runway-aligned
or straight-in approaches are about 25
times safer than the “circle-to-land” procedure.
In Australia, CFIT accidents accounted
for 19 aircraft accidents in the five years to
the end of 2001. A large reduction in the
number of circling approaches conducted,
and more approaches that position aircraft
lower and closer to the landing threshold,
should improve this statistic.
Night VFR pilots will have the advantage
of being able to use the TSO-C129 standard GPS as an alternative to the ADF or
VOR in satisfying navaid requirements.
The new rules will permit them to safely
fly to a “non-aid” aerodrome without the
mandatory navaid alternate within one
hour flight time. Operators of Night VFR
aircraft will also now have the option to
“
The avoidance of
circling approaches is
expected to reduce the
amount of high workload
flying at low altitude often
associated with controlled
flight into terrain.
”
replace their trusty ADF with a modern
GPS receiver capable of greater accuracy.
Pilots unfamiliar with how their GPS
units can now be used need not worry as
the CASA will release an advisory publication providing guidelines for using satellite
navigation. An amendment to CASA’s
Flight Crew Licensing delegate’s handbook
will also be added to support the changes.
IFR and night VFR pilots should ensure
that their GPS databases are current to
meet the accuracy and integrity requirements of the new GPS operations. In the
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past the cost of the database amendment
service has been quite high, but annual
subscriptions for the necessary upgrades
can now be purchased online at a considerably lower price.
Forward to the future: The latest GPS
regulatory changes probably represent the
full extent of the approvals possible for the
TSO-C129 standard equipment. As the
C129 cannot be used for sole means GPS
navigation, CASA advises operators to
carefully research the potential for upgrade
of the C129 equipment prior to purchase,
and possibly even consider holding out for
the new TSO-C145 and TSO-C146 standards currently being slated for operational
approval by CASA.
The two new standards are expected to
be on the market in 2003 and contain a
wide variety of improvements, including
fault detection and exclusion, a better
receiver autonomous integrity monitoring
algorithm, a more standardised humanmachine interface and the ability to use
geostationary satellite GNSS augmentation.
Other GNSS developments in the
pipeline include the SCAT-1 precision
GPS approach on Norfolk Island, the
Burnett Basin automatic dependent
surveillance – broadcast trial, GPS
approaches with vertical guidance, the
introduction of ground based augmentation system precision approaches at
Sydney and support for Airservices’ experimental ground-based regional augmentation system.
While safety continues to be the paramount driver for the GPS reform package,
the aviation community is also likely to
benefit operationally and financially from
further GNSS approvals.
A cost-benefit study undertaken by
Booz-Allen and Hamilton in 1997
predicted large financial benefits for the
Australian aviation industry once a GNSS
augmentation program to support “sole
means” en-route, non-precision approach
and precision approach capabilities was
introduced.
CASA is now involved in an update to
that study as part of a review of Australia’s
future navigation infrastructure.