I'm standing on the concourse watching an Alaska Airlines 737 jet landing in poor weather at Washington DC's Reagan National Airport.
Flight four from Seattle is "greener" than others that touch down here.
It's engines are powered, in part, by a sustainable biofuel. Twenty per cent is used cooking oil, 80 per cent traditional aviation fuel.
Alaska's CEO Bill Ayer, says: "The engine operates exactly the same. All of the parameters, everything that we measure technically about engine performance is identical."
Alaska Airlines says if all its aircraft were powered this way for one year it'd be like taking 64,000 cars off the road.
Other carriers are testing green fuels too.
Earlier this month United Airlines flew the first US commercial flight from Houston to Chicago on a biofuel made from algae.
In June the giant US plane maker Boeing flew a commercial jet plane across the Atlantic using a plant-based biofuel.
So, airlines are giving green fuel a go but it can be expensive: The biofuel made from used cooking oil costs Alaska Airlines six times more than normal jet fuel. After three weeks flight four will go back to using regular aviation fuel and a company spokesperson says there are no immediate plans to try again.
Meanwhile, the European Union is forcing Europe's airlines to go green.
There's no such mandate in the US - though obviously airlines wishing to fly to Europe will have to fall in line.
In the US, the military has taken a lead in pushing for greener aviation, but high costs and insufficient supplies are a drag.
Joanne Ivancic advocates for biofuel technology through her website Advanced Biofuels USA.
"First we need to bring down the cost of the technology and the feed stock so that these airlines can afford to buy this fuel. The second thing is we need the policy to say this is really important."
Aviation analysts like Washington DC-based Peter Goelz say a perception among many Americans that global warming isn't real also holds back green aviation development.
"The global warming deniers, of which there are a significant portion particularly in the Republican party, are going to have to accept the fact that the rest of the world already accepts that global warming is occurring and that we can do something about it."
Were that to change, he says, significant investment in green aviation from the US government would most likely follow - even in these dark economic times.
Until then initiatives like Alaska's are likely to generate good publicity, but make only a fraction of a difference to the environment.