Originally Posted by Ghoulish

Since no system is perfectly efficient in converting energy, aviation biofuel cuts net carbon emissions by 80% (per an EU white paper)

Very conservatively burning at a likely minimum of 2x, the inefficiency of low capacity small business only aircraft easily bumps that to 3x per passenger mile vs the most efficient commercial aircraft in service. It's probably much worse, 4 engines are going to be less efficient than 2 no matter what.

So 40% lower emissions at best thanks to fuel gluttony.

But there's a much larger problem.

Sustainable aircraft fuel costs 8x more than conventional fuels!. With major taxpayer subsidizes. Yes, economies of scale should bring that down, but increasing demand will likely outpace the glacial pace of refinery construction. Many airlines are promising to increase the use from 1% to 5% in coming years, straining capacity, keeping prices high.