In July Airbus released its vision of what a passenger jet will look like in 2050 - a graceful, spaceship-like vessel brandishing long, slim wings, semi-embedded engines and a U-shaped tail - but the planemaker says that around 9 million tonnes of fuel and 28 million tonnes of CO2 emissions could be saved every year in Europe and the US by optimising aircraft systems, shaving 13 minutes off journeys and saving passengers over 5 million hours of flight time a year.

"We can do things to make the aircraft more efficient... more eco-efficient, but in order to meet the targets that we've set ourselves in the long-term we have to have a more holistic approach," says Andy Gordon, Airbus's director of strategic marketing and analysis.

Air traffic control technology, however, is some way behind airplane technology, with multiple organisations around the planet managing the Air Traffic Management ATM.L systems. Two programmes, NEXTGEN in the U.S. and SESAR in Europe, are currently in operation to evolve the ATM system. Deployment is scheduled for 2014.

Though the aviation industry as a whole has reduced fuel burn and emissions by 70 percent in the last 30 years, the total number of passenger aircraft is predicted to double from a current crop of around 15,550 to 32,550 by 2031 according to the latest forecast by Airbus, the world's largest manufacturer of such jets.

With a sky chock-full of planes, the aviation industry has set a target for carbon neutral growth by 2020; in 2050, emissions should be halved compared to 2005 levels.

FLIGHTS OF FANCY

The latest instalment of "The Future by Airbus", a mammoth sustainable aviation exercise, is tagged "Smarter Skies" and focuses on forward-thinking concepts which, if implemented, would reduce excess waste in time, fuel and emissions.

One is the sci-fi suggestion of "free flight", where intelligent aircraft rather than air-traffic controllers select the most efficient and eco-friendly routes. High-frequency routes would benefit from bird-like formations of aircraft that seek to alleviate drag reduction.

Tests with Airbus's A400M military aircraft have, according to Andy Gordon, shown that there are significant benefits to bird-formation flight patterns, where craft can fly as much as one kilometre apart.

Another concept is already in a test phase: The TaxiBot is an electric tug that tows an aircraft from gate to runway, allowing engines to be switched off sooner for fuel and emissions savings.

Environmental groups, though happy for the industry to be focusing on sustainability issues, say technical tweaks are by no means enough.

Keith Allott, head of climate change for WWF UK points out that projections on the rapid growth of emissions, and wider climate impacts, already have these kind of improvements factored in.

"Technical improvements to aircraft efficiency are welcome, but they are no way enough to get global emissions levelling out let alone decline."

"We must also be realistic about the rate of penetration of new technologies," Allott adds. "There is a long life span of existing stock in the world's aviation fleet."

PLANES DON'T POLLUTE, PEOPLE DO

The only real way to reduce emissions, thinks Allott, is for people to decide against buying into a model of unrestrained growth, and make a choice whether they need to fly quite so much.

In July, Airbus released the results of a 10,000-strong survey, the second in two years, to quantify public perception of air travel's future. It found that over 60 percent of people worldwide want to fly more by 2050, though almost all - 96 percent - believe aircraft need to be more environmentally efficient.

Another emission-reduction option is biofuel. One of Airbus' concepts is a renewably powered acceleration technique which could allow steeper climb from much shorter runways than are in use today, and the use of sustainable biofuels and alternative energy sources like hydrogen or solar power.

Allott does see some strong theoretical proposals for biofuel to play a role, but warns that there will never be enough to go around in a world where everyone wants to fly all the time.

"As we begin to run out of readily available fossil fuels," he told Reuters, "we just don't think there's enough bio energy available to fulfil unrestrained growth in aviation."

(Editing by Mark Kolmar)

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