A recent
flight demonstration of a new procedure permitting altitude changes at cruise
levels in oceanic airspace should soon allow airliners to burn
less fuel and reduce
carbon dioxide emissions on transatlantic flights.
The
Airbus-led CRISTAL ITP test, which involved two Airbus widebody jets — one
operating a scheduled passenger flight — cruising west over the ocean south of
Iceland, was very successful, said Airbus executives Stephane Marche and Thomas
Fixy. Marche is project leader for CRISTAL ITP, while Fixy is Airbus'
Multi-Program Manager and oversees a variety of programs that include CRISTAL
ITP.
"From
operational perspectives, there was good acceptance (of the results of the
test) by controllers and pilots," said Fixy and Marche. "We believe
we can achieve a timely implementation of this procedure ... We are quite
optimistic it will be implemented around 2010 operationally over the North Atlantic."
At present,
airliners cruising over the world's oceans are generally unable to change
altitude to improve their flying efficiency or take advantage of favorable
winds. This is because oceanic airspace beyond a certain distance from land
cannot be controlled by radar, which has limited range.
Consequently,
controllers and pilots rely on "in trail" procedures to maintain safe
distances between aircraft cruising at the same altitudes. These distances are
maintained by ensuring that each aircraft at a particular flight level on a
given track is flying in the same direction, that each is cruising at the same
speed, and that all aircraft are at least 10 minutes' cruising time apart from
each other. The 10-minute time interval equates to about 80 nautical miles at
commercial-jet cruise speeds.
Changes in
cruise altitude which cannot be monitored by radar aren't generally allowed
because they could compromise the minimum specified in-trail separation between
aircraft.
However, in
late March the partners in CRISTAL ITP (the 'ITP' standing for 'In-Trail
Procedure') used satellite-navigation-based Automatic
Dependent Surveillance—Broadcast (ADS-B) technology to demonstrate safe
cruise-altitude changes in oceanic airspace. ADS-B is now being developed
internationally to replace radar as the world's primary method of air traffic
control (ATC) worldwide by the early 2020s.
Test was
radar-monitored
The
airspace in which the demonstration took place was close enough to Iceland that
the two aircraft involved were radar-monitored by controllers at Iceland's ATC
provider Isavia at all times during the test, and so safe separation between
them could be ensured, said Marche and Fixy. Isavia and the UK ATC provider
NATS are partners in CRISTAL ITP, as are Airbus, SAS, and Eurocontrol CASCADE,
the program coordinating the planned implementation of ADS-B throughout the EU
by 2015.
One of the
two jets, a Scandinavian
Airlines Airbus A330 cruising at flight level 310 (a standard pressure
altitude of 31,000 feet) on a passenger flight to North America, acted as a
reference aircraft for the demonstration. The A330 was fitted with the 'ADS-B
Out,' GPS-derived, position-broadcasting technology already certified for all
modern Airbus jets. This jet didn't change altitude and constantly broadcast
its position and altitude to the controllers in Iceland and in the UK who were monitoring the demonstration.
The other
jet, Airbus' own A340-600 test aircraft, was fitted with new 'ADS-B In'
technology that allows pilots of aircraft to see the positions and altitudes of
all other aircraft in the area. ADS-B In receives direct positional information
from aircraft using ADS-B Out and also can allow an aircraft to receive Traffic
Information Services—Broadcast (TIS-B) data on aircraft positions and altitudes
broadcast by ATC providers.
As a
result, the pilots of the Airbus test A340 could assess the distance between it
and the SAS aircraft at all times during the test and request controller
clearance for altitude changes when the aircraft were at safe distances.
Demonstration
involved four steps
The
demonstration involved four separate steps. In the first, the A340 climbed from
flight level 290 to flight level 320 from a position ahead of the SAS A330. In
step two, the A340, still ahead of the A330, descended again to 29,000 feet.
Then the
A340 performed an orbit maneuver at that altitude to let the SAS A330 pass by
2,000 feet above the Airbus test jet. From the A340's new position behind and
below the A330, step three involved it ascending to flight level 330. Step four
was a descent from flight level 330 back to flight level 290, still behind the
SAS aircraft.
Airbus is
now analyzing the CRISTAL ITP ADS-B data from its flight-test A340, comparing
it with the data obtained during the test from the Isavia radar at Reykjavik
and with simulations run at the NATS Shanwick oceanic ATC simulator in linkage
with Airbus' own ATC simulator.
However, it
is clear that during the demonstration the two aircraft never came closer to
each other at the same altitude than 25 miles, said Fixy and Marche.
Separation
safely reduced
Also, the
data suggest that when operational the CRISTAL ITP procedure will be precise
enough that controllers will be able to reduce horizontal-separation distances
between cruising jets to 10 nautical miles as they change altitudes, allowing a
great deal of operational flexibility.
Airbus
fuel-burn data suggest CRISTAL ITP would produce a 170-kilogram average fuel
saving on a transatlantic flight for an aircraft the size of an A340-600. For
aircraft now constrained by ATC requirements to fly 2,000 feet below their
optimal cruise altitudes, the saving could reach 760 kilograms, said Marche and Fixy. And the larger the aircraft, the larger the saving — A380s or 747s would
save more fuel than A340s.
On average
some 400 commercial jets fly westbound over the North Atlantic every day and
some 300 fly eastbound, according to Airbus; at these traffic rates, CRISTAL
ITP could produce a total fuel saving of some 120,000 kilograms a day.
Even though
the FAA isn't mandating ADS-B for all U.S. airspace until 2020, transatlantic
flights will start seeing flight-efficiency benefits from its use much sooner
than that. ADS-B is being introduced in remote, less densely trafficked
airspace first. It is already in use for half of Australia's airspace, and is
being introduced over Hudson Bay in November.
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