Any flight can be accelerated for additional fuel. Simply open the window of current flights and tap the option Accelerate for X fuel. Then the plane will instantly return from its flight and appear on the runway.
This is a game feature that necessary items for upgrading a Fuel Station to level 3 start dropping after you get the corresponding quest. To get it you need to complete the previous quest that asks to upgrade your Fuel Station to level 2 and get some items. Both tasks are given by the engineer.
To get the destinations under question available you should activate the flight maps that can be received from the chest. This box itself can be obtained for the rocket launch performed with your neighbours from the second launch pad. Please, note that you should take the first place in the rating among the participants.
To use the flying accelerator you need to open the Flights menu in the game (press button with a plane depicted in the lower left corner of the game window and choose the Flights tab). When a plane is in a flight its symbol is shown under the arrow that stands for the way duration. At a certain period of time it is highlighted with a green colour. At this moment you should press the arrow and choose the accelerator.
Open the Flights menu and find the flight you'd like to learn about. Then tap the flight picture in the shape of the post stamp. In the pop up window you will see the information on the number of flights you need to take to get the skill stars.
Open the flight menu (plane icon on the lower toolbar) and you'll see a list of places you can send your planes to. Each flight is suited to a particular type of plane, and no other planes can do it. Furthermore, each flight requires a specific number of passengers (suitcase icon) and fuel (barrel icon), and certain flights require additional items. If you have the right plane, the right number of passengers and fuel, as well as the required items, press the Fly button. Your plane will automatically appear on the right runway. You then need to tap it several more times to fuel it, board it and signal it to take off.