Numerical techniques have become very practical and effective in dynamic simulation for large systems. However, till date, computational modelling of fuel in auxiliary fuel tank during aircraft fuselage section crashworthiness remains a challenge to solve. Previously, four different fluid modelling techniques, namely, Lagrange, Euler, Arbitrary Lagrange Euler (ALE) and Smoothed hydrodynamics particle (SPH) have been investigated to represent fluid in different applications ranging from marine science to rotorcraft fuel tank crashworthiness. However, for a full-scale aircraft fuselage section with auxiliary fuel tank, fluid modelling has not been yet reported. Therefore, in this current research, a commercial explicit dynamic code Autodyn is adopted to solve Fluid-structure interaction (FSI) problems numerically on a standalone civil aircraft type fuel tank with four different fluid models, respectively, i.e. Lagrange, Euler, Arbitrary Lagrange Euler and Smoothed Hydrodynamics Particle. Virtual drop tests are conducted with a vertical impact velocity of 7 m/s to investigate the most suitable fluid model, which can be further utilized to represent fuel inside an auxiliary fuel tank in a fuselage section to study the crashworthiness. After studying the structural deformation, von Mises stress, equivalent plastic strain, absorbed internal energy, fluid sloshing events and computational time duration due to the adoption of different fluid models, it is found that Lagrange fluid model with the node erosion algorithm setup suits best to the fuel. In the second part of the research, crashworthiness of a full-scale fuselage section with auxiliary fuel tank considering fluid as Lagrange model and fluid as distributed mass is investigated. Results are compared with the available experimental and numerical outcomes and it is found that, modeling the fluid inside of an auxiliary fuel tank is crucial to capture the appropriate plastic deformation of the fuselage section; however, presence of fluid does not affect the acceleration responses of the cabin floor.