Final answer:
Emergency landing fuel is a reserve fuel carried by aircraft for use in emergencies, which could potentially include high-cetane rating biodiesel. Biodiesel is derived from biological sources and is being explored as a renewable alternative to conventional aviation fuels.
Step-by-step explanation:
Emergency landing fuel refers to a reserve of fuel that an aircraft carries specifically for emergency situations, such as an unexpected need to divert to an alternate airport or to spend additional time in the air due to unforeseen circumstances.
The characteristics of this fuel need to be such that it can be relied upon under different conditions, and it often has a high energy density to maximize the energy available in emergencies without significantly increasing the weight of the aircraft.
In the context of alternative fuels, a substance with a high cetane rating of 56-57, such as certain biodiesel blends, could indeed serve as emergency landing fuel. Biodiesel and other renewable fuels, such as ethanol, are derived from biological sources like algae, sugar, corn, and rapeseed, and they are being considered as potential substitutes for traditional petrochemical aviation fuels.
Moreover, the use of biodiesel as a potential emergency landing fuel in diesel engines may also reduce the additional energy required to manage the fuel's weight and therefore can support aircraft efficiency.