Increasing trend of air traffic leads to the congested airspace and overwhelmed air navigation service providers. New procedures and technology are implemented every day, but with rigorous testing. Simulations are a part of that testing, but every simulation is as good as its model. Within the traineeship in Eurocontrol, the current Base of Aircraft Data Family 4 (BADA 4) is analysed and searched for the possible improvements in the segment of the piston propeller powered aircraft. The model for these aircraft isn’t as good as it could be, and at this point it is necessary to improve it due to the fact that the number of general aviation aircraft (mostly piston powered) is increasing. During research and validation of the initial model it was determined that some improvements need to take place in engine power modelling alongside with the propeller efficiency modelling. Cruise data as a primary source for drag polar coefficients and vertical speed conversion to the rate of climb were introduced. With all of these corrections, or improvements, correct performance data was reproduced to resemble the performance data published in the aircraft’s manual. At a certain point to gain an insight into the published performance data, and to gain some additional data, two flight tests took place. As a result of flight tests, the published data was confirmed throughout usage of different data reduction methods. In conclusion, certain improvements were established, and proposed to the Eurocontrol team. Implementation of these improvements into the Eurocontrol BADA 4 tool will be done by Eurocontrol team at a certain point, if they determine that these proposed changes do bring a necessary improvement their model.