I don’t know much about aviation industry, but I have some general advices. You should start thinking about problems users will be able to solve.
Look at whole process of fuel refilling, maybe there are some problems, which are really a pain in the neck. For example, it is really hard to find good fuel transporter? Why not make functionality for searching transporting companies with prices, reviews, etc. Maybe there are some documents needs to be signed for fuel refilling, why not integrate with cloud sign service and give users ability to create and sign this documents in app?