Yes, there's algae on the plane. Why do you ask?

The economics of air travel were signficantly affected by the September 11th attack, but one thing has remained constant both before and after September 11 - you need fuel to make the planes run. BusinessWeek quoted from a Spiegel Online interview:

[T]he oil price has changed rapidly. But it has done that many times before and it will continue to do so. Even today, the highest operating expense for an airline is fuel. It remains a priority to find a way to mitigate that situation.

The interviewee, who is from Boeing, then talks about biofuels.

That is why Boeing is trying to open up this avenue of alternative fuel. It can help that situation while having a better environmental performance at the same time....

The first test flight was in February 2008. But more recently, in December 2008 and in January 2009, there were three test flights in quick succession with a higher blend of biofuel and better performance. We have already achieved quite a bit in terms of technical understanding and technical qualification.

The Spiegel Online interviewer then asked a critical question which needs to be asked of any plant-based alternative fuel source:

How do you plan to ensure that the crops needed for biofuel production do not endanger food production or contribute to deforestation?

The Boeing rep spoke of "sustainability criteria" and "avation-specific discussions."

But then the Spiegel Online rep got into the "how big is it" discussion.

[L]et us talk about algae. How big do these cultures need to be?

Boeing's response:

The optimists say, to supply the entire world with aviation fuel, you would perhaps need an area of the size of Belgium. We still need quite a bit of research and development work to really determine whether that is possible. So far, we are very pleasantly surprised by the innovation and the progress.

Let me clarify that they were just discussing an area the SIZE of Belgium - they WEREN'T talking about covering Belgium itself in algae.

However, Ariel Schwartz at FastCompany notes that you don't have to use exotic fuels to save money:

Air India, the country's national airline, has saved $9.26 million over six months with simple energy-saving techniques.

The airline has cut contingency fuel from 5% to 3% and decreased aircraft weight by reducing the amount of water, the weight of food carts, and the magazines on board....Air India also now flies in a straight line at optimal altitudes and speed, practices a "continuous descent" approach during landing, uses a single engine during taxiing, and derives pre-flight power from sources on the ground.

And they didn't need a Belgium-size fuel "plant" to do it.

And, as BusinessWeek notes, biofuels prices are volatile themselves. But, as the Riverside Press-Enterprise notes, there are more entrants into the market.