It is increasingly clear that breaking aviation’s dependence on fossil fuels to achieve the ambitious objective now being set by some governments for achieving carbon-free flying as early as 2040 will involve several technological stepping stones. In the short term, one of these is sustainable aviation fuel (SAF) in which, to varying degrees, the oil content is reduced in a switch to so-called biofuels. Electric propulsion—either based on a hybrid system that still includes some kind of turbine engine in the powertrain or all-electric using just batteries—is another. But few experts would claim that any of these approaches are some kind of Holy Grail of sustainable flight.
Let’s start with batteries. Although they offer an excellent way to reduce emissions, the energy cost is not the same as that associated with traditional jet fuel. Furthermore, because of energy density challenges, the range just isn’t there for most commercial air transport operations.
