Stackless flights trim transatlantic carbon output

Scandinavian Airlines (SAS) has demonstrated the kind of incremental environmental benefits that can arise when new technology is applied to an existing business with the aim of reducing emissions.

On 8 December this year, SAS completed a flight from New York to Sweden that followed a so-called "green approach" flightpath to Stockholm’s Arlanda Airport. Rather than cruising at normal speed across the Atlantic and then joining a stack of aircraft awaiting landing permission near its destination, the Airbus A330-300 followed an Advanced Continuous Descent Approach (ACDA) profile.

Under ACDA, the aircraft's computerised systems exchange data with ground-based air traffic control computers. The two co-operate to adjust the speed of the incoming aircraft so that it arrives at the airport exactly in time for its landing slot.

"The approach carried out at Arlanda today was in fact very easy for us pilots," said the flight's first officer in a statement. "The engines were running at idle power from our cruise altitude, until the final stage of the approach. The aircraft's flight management system was automatically flying the whole approach routing and the passengers [perceived] the approach as nothing but smooth and quiet."

ACDA minimises engine power during the cruise and aims to eliminate waste during stacking. It can also cut noise in the vicinity of the airport. SAS said that the single Airbus flight, carrying 260 passengers, saved about 150kg of aircraft fuel and 470kg of CO2 emissions by optimising its approach.

SAS did not say what percentage saving this represented, but a fully-fuelled A330-300 carries 69,000kg of fuel, implying that the economy increment is less than one percent. However, given that there will be more than a quarter of a million transatlantic flights this year, the cumulative financial and CO2 savings of ACDA would clearly prove substantial.

Also, SAS's trial was conducted during an off-peak flight, and thus is likely to represent the miniumum fuel savings possible. Flights arriving at busier times are much more likely to spend time in holding-pattern stacks.

As well as the recent transatlantic trial, SAS has also carried out over 2,000 ACDA flights within Sweden.

The ACDA experiment is a part of the Atlantic Interoperability Initiative to Reduce Emissions (AIRE), a joint programme kicked off by the European Commission and US Federal Aviation Administration in June this year.