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When a Virgin Atlantic jumbo makes a planned 1 hour and 20 minutes hop from London to Amsterdam later this month it will be one of the most closely analysed flights in aviation history.
The journey, without passengers, could answer the aviation industry's prayers, as it will be powered by a a mix of 20 per cent of a so-far secret biofuel and 80 per cent conventional jet fuel.
Work on converting an aircraft to run on biofuel has been done in earnest for the past three years, and Virgin hopes that biofuel-powered aircraft could be operating commercially within five years - if the fuel works at high altitudes and is compatible with delivery infrastructure.
The planned Virgin flight is not the only entrant in the race to test green fuel - Air New Zealand is part of a separate joint project with Boeing and Rolls Royce to develop an environmentally-friendly alternative.
For all the world's airlines, the test offers hope on two fronts: perception and the bottom line.
An active green movement is scrutinising every gram of polluting carbon dioxide that airliners produce. And it's also about survival, with the high cost of oil already claiming weaker, niche airlines.
International Air Transport Association figures show the spike in fuel charges will add US$14 billion to the industry fuel bill this year, to US$149 billion, based on an average price of US$78 per barrel.
At present air travel contributes 2 per cent to 3 per cent of climate-change gases, but that level is increasing.
The industry is investing in lighter aircraft and new engines that are claimed to be as fuel efficient as a family car, given the number of passengers they carry, but biofuels could minimise dependence on oil.
In Europe in particular airlines are battling green groups which say no matter how fuel efficient planes become, the more air travel, the more pollution.
And while the the impact of carbon emissions is well known, there is uncertainty about the effect on global warming of oxides of nitrogen and vapour trails, known as contrails, at high altitudes.
Virgin has been working with Boeing and General Electric to create hybrid aircraft, similar to the cleaner fuel concept for hybrid cars.
Neither the aircraft nor its engine will need to be modified to use the biofuel.
Virgin will outline what fuel is being used at the time of the test flight, likely to be later this month.
The airline has declined to comment on whether the "green" fuel will be made with algae, something that Boeing is testing, but says the fuel will be sustainable and is a product that will not displace food crops.
Of all airlines, the need to be green is most pressing for Air New Zealand, where fuel costs account for more than half of all expenses on long-haul flights.
Research by the University of Otago released earlier this month showed carbon emissions from visitors' air travel to New Zealand equalled total emissions from the country's coal, gas and oil-fired power generation.
Unlike other airlines, where guaranteed revenue comes from business travellers, Air New Zealand relies on leisure travellers for around two-thirds of its revenue. Many of this group would look for the greenest carrier, or worse still, not come to New Zealand at all.
Air New Zealand chief executive Rob Fyfe has been warning of that risk for the past two years.
"If you're living in Europe you can do a lot of the things you travel to New Zealand to do on your doorstep," he says.
But he sees an opportunity for this country, and by extension, his airline.
"If we ... can stand up and say we as a nation are going to make a difference in terms of climate change, then there's the opportunity to create a point of difference."
This could extend to biofuel development, more sustainable pastoral farming, or work on technology to create clean-burning coal.
"We quite genuinely believe visitors will be attracted to New Zealand in an eco-environmental context and we see that is quite a legitimate and genuine motivation to drive our visitor numbers and tourism here."
Air New Zealand is aiming to becomethe greenest long-haul airline in the world.
The airline uses around eight million barrels of jet fuel a year which costs around 20 per cent more than quoted crude prices, so the economic imperative is strong.
"By maximising our commercial interests we're maximising the environmental benefit - they're totally aligned."
Some have described the green push as a fad, but Fyfe says passengers have told the airline they want to fly on a carrier that demonstrates it is taking an environmentally responsible approach.
"I have no doubt that people will pay a premium to fly in an environmentally considerate way - I think this is a way to create a value-added product or service for our customers."
While the airline is likely to be beaten to the considerable publicity of being first to fly on green gas, he says work on the biofuel project in conjunction with Boeing and Rolls Royce is making good progress.
It is hoped to have an Air New Zealand Boeing 747 airborne with one of its four engines isolated to run on biofuel by the end of the year.
Computer modelling work was being done at Boeing's Seattle base.
Much of the research was concentrated on an oilseed crop, jatropha, a woody plant that can grow on barren, marginal land; and algae, high in oil content and able to grow on sewage ponds and in seawater.
A Nelson-based firm, Aquaflow, which already has algae-based biodiesel for land vehicles in production, says it has been visited by Boeing representatives working on alternative jet-fuel projects.
Fyfe says Air New Zealand will run an engine in a test bed at the airline's Auckland engineering base before flight tests.
While an enthusiast, he is cautious. There were freezing-point problems to overcome - some biofuels gel at extremely low temperatures - and uncertainty about how corrosive alternative fuel is.
"Ultimately you need to have confidence you have a fuel which can use the existing fuel movement infrastructure such as pipelines and tankers. If you have to recreate that infrastructure, the hurdle becomes very high."
Air New Zealand has yet to take the plunge into one visible plank of the airline industry's green push - passengers voluntarily buying carbon credits.
But it aims to follow the trend this year.
"We've found for a lot of people it doesn't really cut the mustard. They sit there and say 'if I fly on this aircraft that creates an emission or carbon footprint, paying money into something doesn't really make my guilt go away'.
"As a consequence these voluntary offset schemes have been spectacularly unsuccessful - maybe 1 or 2 per cent of passengers contribute," Fyfe says.
"We will introduce an offset scheme if that's what passengers want - but we're looking to do something cleverer - can we allow our people to invest in something that has a more tangible benefit that they can relate to."
This could be the creation of a forest or conservation estate.
"We would give you the opportunity to donate funds and visit that estate as part of your visit to New Zealand."
But it's incremental work that is already making a difference for Air New Zealand.
In a decision that "wasn't universally popular", footrests have been taken from the economy section of transpacific 747s, saving a tonne in weight and about 500 litres of fuel on an Auckland-Los Angeles flight.
Cockpit paperwork is now in electronic form, engines more regularly washed with a citrus-based cleaner are up to 3 per cent more efficient, and agreements with Chinese and Russian authorities have shaved 30 minutes off flights over those countries.
And then there's the new planes. Boeing's next airliner, the 787 of which Air New Zealand has eight on order, is expected to use 20 per cent less fuel and be 60 per cent quieter than the 767 model it replaces.
Cathay Pacific announced a voluntary carbon offset scheme late last year where passengers are effectively supporting a Chinese wind farm. The airline's New Zealand manager, David Figgins, says emissions are a fact of life, but it was impossible to restrict aviation.
"Originally, fuel saving was driven by economics before the issue of global warming raised its head, but now it's becoming the issue of how we keep this thing going in the meantime."
Pacific Blue allows travellers to voluntarily offset flights from 50c per domestic sector and from $3 per international sector, to support a Palmerston North renewable energy project where landfill methane gas is captured and used to generate electricity.
Board of Airlines Representatives director Stewart Milne says carbon mitigation programmes with the associated feel good factor just encourage more to fly.
"No matter how efficient planes are, how many trees are planted per sector there's no escaping the fact aviation pollutes and will continue to do so."
What passengers think
Eloise Gibson samples views at Auckland Airport on aviation going green
KERRY KAKAHI
Age: 33
Nationality: New Zealander
Travelling to Thailand for a holiday
Do you worry about the environmental damage planes do?
I haven't actually thought about it that much. I've thought about environmental damage for other things but not that.
Would you pay a carbon offset charge?
I'm not sure. It depends on how much of a difference it was. If it was an extra $20 it wouldn't make much difference but if it was an extra 10 per cent it would, especially on a long-haul flight.
Would you pay more to fly on a biofuel powered plane?
Again, it would depend on how much it was in comparison to a normal flight.
AMBER SHERGIS
Age: 22
Nationality: Australian
Travelling to Perth for a holiday
Do you worry about the environmental damage planes do?
No.
Would you pay a carbon offset charge?
Honestly I don't think planting trees to offset carbon emissions makes enough difference to the planet. I think it's more a way to get people to pay yet another charge. There are more significant initiatives they could embark on and that goes for other companies too. They could look at providing more recycle bins, printing tickets on recycled paper, using more solar power and being more energy efficient.
Would you pay more to fly on a biofuel powered plane?
It would depend where I was travelling to. On a short flight I could afford to pay a bit more but, if it was a long one, the extra might make it too expensive.
BILL BENT
Age: 64
Nationality: New Zealander
Travelling to Vanuatu for a holiday
Do you worry about the environmental damage planes do?
I haven't thought about it.
Would you pay a carbon offset charge?
I'm not convinced the money would go where they said it did.
Would you pay more to fly on a biofuel powered plane?
I'm concerned with the pollution of the planet but I don't think biofuel is the answer. The moment they shift edible crops like corn to biofuel, it affects poor people because it puts up the cost of basic food crops. I think it's politically expedient to talk about it at the moment but it's crazy to start cutting down trees for land to grow biofuel.
ELIZABETH TRUNZER
Nationality: Canadian
Travelling from Canada for a holiday
Do you worry about the environmental damage planes do?
Yes. But I don't think planes are always the problem. I worry more about the culture we have now where people just throw things away, which I've noticed is not the case in New Zealand. Everyone picks up after themselves, it's clean. The way we live now, I think flying is a necessary evil. It's difficult to swim from Canada.
Would you pay a carbon offset charge?
No.
Would you pay more to fly on a biofuel powered plane?
No, because I don't think it's necessary. I think the airline companies should do it themselves. It's like the oil industry, banks and other companies are all making mega-bucks and they want the little guy to pay for it.
JOEL COLLINS
Age: 19
Nationality: New Zealander
Travelling to Perth to study.
Do you worry about the environmental damage planes do?
It hasn't crossed my mind.
Would you pay a carbon offset charge?
I suppose so. I don't know.
Would you pay more to fly on a biofuel powered plane?
I'd rather save my money.
MIKE AND ANGIE CHANNON
Age: Both 55.
Nationality: English.
Travelling from England for a holiday.
Do you worry about the environmental damage planes do?
Mike: Yes. With the number of planes these days and the number of travellers, we just worry about transport emissions in general. But when you live in the UK and you've wanted to come to New Zealand all your life there aren't too many other ways to get there! I don't run a car now, that's how I justify it.
Would you pay a carbon offset charge?
Mike: I'm pretty sure once it gets established you'll have to find a way of offsetting your travel. I'd prefer private companies to collect it than the Government.
Angie: I think most of it would end up going on administration.
Would you pay more to fly on biofuel-powered plane?
Mike: It depends how much more it cost.
