SAS Completes Transatlantic 'Green' Flight

posted: 12 December 2007 01:53 pm ET

: Scandinavian Airlines System has become the first European airline to carry out a fuel-saving 'green' approach on a transatlantic flight, performing a successful continuous descent approach (CDA) with an Airbus A330-300 operating a flight from Newark to Stockholm Arlanda with 260 passengers onboard. SAS is carrying out CDA trials as part of the Atlantic Interoperability Initiative to Reduce Emissions (AIRE), a joint U.S.-Europe project involving airlines, manufacturers and air traffic management service providers. Credit: Scandinavian Airlines System

Scandinavian Airlines (SAS) has become the first European airline to complete a transatlantic flight with a "green" descent profile designed to reduce fuel consumption and CO2 emissions.

On Dec. 8, SAS flight SK904, an Airbus A330-300 from Newark to Stockholm-Arlanda Airport with 260 passengers on board, performed a successful continuous descent approach (CDA) to Arlanda using flight-idle power. For a continuous descent to be possible, air traffic control (ATC) must not require the aircraft to level off and hold at an intermediate altitude during any part of the descent.

"The system is based on arrival punctuality," explained Alain Siebert, head of Scandinavian Airlines' Fuel Cost Saving Initiative. "An optimal trajectory to a specific arrival time is given" by ATC, and then -- taking account of wind speed -- the pilots manage the speed of the aircraft throughout the descent to ensure that it lands at the designated arrival time.

SAS estimates the A330's CDA saved approximately 150 kilograms of fuel and produced 470 kilograms less CO2 than a usual descent and approach would have generated. In performing the trial flight, SAS became the first European airline to demonstrate its commitment to the Atlantic Interoperability Initiative to Reduce Emissions (AIRE).

AIRE is a joint FAA-European Commission initiative involving several airlines and national aviation authorities on both sides of the Atlantic, as well as manufacturers Boeing and Airbus. In addition to SAS, European airlines involved in AIRE are Air France-KLM and Virgin Atlantic Airways, while in the United States Delta Air Lines and UPS are involved.

Lots of coordination involved

Preparations for the CDA involved coordination among the airline, the Swedish state-owned service com LFV, Airbus, and Stockholm-Arlanda Airport, said Siebert. On Dec. 8, coordination between the aircraft and the Norwegian and Swedish ATC providers -- both involved in controlling the descent -- began 60 minutes out from the A330's designated landing time.

Beginning its descent 25 minutes before landing, the A330 descended from a cruise altitude of 38,000 feet using a 30 percent thrust setting until the last 90 seconds of the flight, when air safety regulations required application of power. At an altitude of 2,000 feet the A330's pilots selected an intermediate degree of flap -- the setting used was '3', according to Siebert -- and landed normally at Arlanda.

"The aircraft's flight management system was automatically flying the whole approach routing and the passengers conceived the approach as nothing but smooth and quiet," said Sigmund Lockert, chief pilot of SAS' Airbus A340/A330 fleet, who few as the first officer on the CDA trial.

SAS is conducting additional transatlantic-flight CDA trials on its three A330 weekend flights from Chicago and Newark to Stockholm until the end of January and will restart the trials in late March or in April, said Siebert.

SAS went for 'least efficient phase' first

"From a prioritization perspective, we went for the least efficient phase of the flight first," said Siebert. The descent is "where the lack of predictability costs the most," in terms of extra fuel burn and unnecessary CO2 emissions. The three weekend flights represent Scandinavian Airlines' "present (AIRE-related) traffic program, but our commitment is to broaden this as much as possible," he said.

Next year, SAS intends to build on research carried out by Lufthansa at Munich International Airport into optimizing ground movements, to minimize taxi time between the terminal and the runway after an aircraft is pushed back at departure.

Also, SAS has requested that it be the first airline to put into effect AIRE research led by the Portuguese aviation authority into optimizing the flight-level and airspeed profile of the second phase of an aircraft's climb after takeoff -- the gradual climb to cruise altitude that follows the initial steep climb-out.

"We would be the airline doing it -- we have expressed our wish to have that set up as soon as possible, next year," said Siebert.

He explained that, when an airline is able to reduce the fuel-burn of any phase of a flight, it has a multiplying effect on reducing CO2 emissions. This is because the aircraft needs to carry less fuel to burn just to transport the weight of the fuel used in that phase of the flight.

2009 goal is entire 'green' flight

Scandinavian Airlines' goal under AIRE is to complete an entire transatlantic "green" flight, gate-to-gate, by late 2008 or in early 2009, said Siebert. "We haven't pinpointed yet" the route on which the trial will take place, he added, but at present SAS is contemplating holding the trial on either Seattle-Copenhagen or Newark-Stockholm.

The airline estimates that if it could conduct CDAs on all its SAS International division's long-haul flights, it would save 492 tons of fuel and would reduce its CO2 emissions by 1,550 tons annually.

SAS also has gained extensive experience in conducting CDAs on short-haul flights, flying more than 2,000 CDA approaches with Boeing 737s to Scandinavian airports. When it began the trials, each 737 CDA saved about 100 kilograms of fuel and reduced CO2 emissions by some 315 kilograms. Now, however, SAS is able to save approximately 150 kilograms of fuel per landing and cuts CO2 emissions by some 470 kilograms.

Airlines hope that the future U.S. NextGen and the Single European Sky Air Traffic Management Research (SESAR) airspace management systems will be in place by 2020, allowing all their transatlantic -- and short-haul -- flight profiles and procedures to be considered "green."