Transatlantic Flights Becoming Greener by 2010

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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