Flying beyond our means – air travel and the environment

Box 2 | Flying smarter

Improving aviation to make it more eco-friendly can take several approaches. The main ones include finding a viable alternative fuel to kerosene; improving plane and engine designs; and adapting air traffic management practices.

Cleaner fuels

Two of the main advantages of kerosene are that it is energy rich (important when a plane has to carry its fuel long distances) and doesn't readily freeze at the low temperatures of cruising altitudes (less than -40ºC). Unless an easily produced fuel with similar properties is developed, kerosene is expected to remain the main jet fuel for decades to come. Testing of biofuels produced from coconuts, Jatropha, algae and other sources is underway but the technology needs further development. Nevertheless, biofuels for aviation can be produced through several processes: fermentation, transesterification and the Fischer-Tropsch process used by Germany in World War II to overcome oil shortages.

Biofuels are divided into two categories: first and second generation biofuels.

First generation biofuels are those that are currently being produced commercially using existing technology. These fuels are produced from crops such as corn, wheat, sugar cane and oilseed crops. But there's increasing concern that first generation biofuels take up valuable land and resources needed to grow food.

Second generation biofuels, on the other hand, rely on promising technologies that are currently being developed for commercial use. They can be made from waste biomass – such as leftover food crop materials including straw or even woodchips. Weeds and dedicated woody energy crops can also be used.

Some commercial airlines are promoting their use of biofuels made from crops that don't compete with food production such as Jatropha, babassu and algae. Air New Zealand for instance, is testing a Boeing 747-400 with one of the plane's four engines running on Jatropha oil. Jatropha plants can be grown on non-arable land and its seeds contain up to 40 per cent oil. But to get commercial yields, Jatropha is sometimes grown on more productive land with the addition of fertilisers and water. In Australia Jatropha curcas has been banned from importation due to its classification as a potential weed.

On the other side of the world, a Dutch airline is trying a different biofuel – made from algae – to fully power its Fokker F-50 planes by 2010. Algae are a promising example of a second generation feedstock for fuel that can be made using ponds of seawater. But further development of the technology is needed, and large areas would have to be set aside to grow the algae.

Although the technology is improving, current biofuels can be limited in their greenhouse gas savings, and can require huge areas of land to grow the biomass. According to one estimate, it would take some 1.4 million square kilometres – more than twice the size of France – to produce enough Jatropha oil to power the world's planes for a year.

New technology

When a two-seater motor-glider with a 16-metre wingspan and propeller took to the skies south of Madrid in April 2008, it represented a new era in aircraft design – one that produced zero carbon dioxide emissions.

Developed by Boeing and several international partners, the Fuel Cell Demonstrator Airplane climbed to over 300 metres powered by hydrogen fuel cells and lithium-ion batteries.

It then cruised at 100 kilometres an hour for a total of 20 minutes, powered only by the fuel cells that converted hydrogen into electricity and heat with the only exhaust being water. But as a greenhouse gas, the emission of larger amounts of water into the atmosphere is of concern. At what point in the future such planes could become a commercial reality is unclear and whether this technology will ever be suitable for large heavy passenger-carrying planes.

Better designs

Many airlines are looking at more efficient plane design to reduce fuel consumption including lighter composite materials, more efficient wings with less drag, and even using continuous welds in place of rivets to hold planes together.

Qantas calls the latest addition to its fleet, the Airbus A380 super jumbo, the 'jolly green giant'. Qantas claims the giant plane has 50 per cent more floorspace than a 747, is 25 per cent more fuel efficient than other large jets, and will need fewer flights than other airlines to move the same number of people.

KLM and others are using vertical 'winglets' at the end of plane wings to improve aerodynamics and claim it can reduce carbon emissions by up to three per cent.

But good ideas take time to take to the air. A general rule of thumb is that new designs might take 10 years to develop, and a further 10 to construct and phase in. Moreover, a given new design will have a certain production lifetime and a subsequent retirement phase. Which means there could be a lag of up to 40 years in which older-style planes would still be used.

Changing flying habits

The International Air Transport Association, the body that represents some 230 airlines, suggests that aviation's effect on climate change could be addressed through combined air traffic systems, shortening routes, better fuel management practices, and improving air navigation. In Australia, such measures are already being looked at.

In 2007, Airservices Australia, which is responsible for air traffic control, initiated a range of ways to reduce greenhouse gas emissions from aviation. These include:

  • better management of aircraft on the ground, with engines off or at reduced power, before departure

  • better prediction and management of aircraft delays and arrivals, rather than see planes waste fuel circling an airport in a holding pattern, and

  • allowing continuous descent approaches that let planes descend at low power, saving as much as 400 kilograms of fuel per arrival.

Research conducted through the University of NSW has already shown a substantial reduction in aircraft noise and emissions by adapting flight paths of aircraft.

Boxes
Box 1. What aviation emissions do
Box 3. Saving our skies – what can we do?

Related sites
Biofuels in Australia – an overview of issues and prospects
(Rural Industries Research and Development Corporation, Australia)
Biomass – the growing energy resource (Nova: Science in the news, Australian Academy of Science)
Aircraft emissions (Airservices Australia)
Building a greener future(International Air Transport Association, IATA )
Fact sheet: Alternative fuels (International Air Transport Association, IATA ) (Note: the classification of biofuels in this fact sheet differs from the above classification)

External sites are not endorsed by the Australian Academy of Science.
Posted February 2009.