In maritime shipboard operations, the typical `skid-type' landing gear of unmanned aircraft systems constrain mechanical securing and traversing options, and present complex ship-helicopter interface behaviour which must be characterized. The planar case of a dynamic interface package named SRAMSS (Skid-equipped Rotary-wing Aircraft Manoeuvring and Securing Simulation) has been developed. SRAMSS models the aircraft as a mass-coupled rigid airframe and flexible landing gear by integration of dynamic finite element modelling into Kane's method. Oriented ship-aircraft contact dynamics is modelled by a Separation Axis Theorem algorithm. Aerodynamic drag, and rotor blade element models complete the modelling of the embarked aircraft. Verification of SRAMSS confirms the proper implementation of the included models. Preliminary validation of the rotor model against published data indicates the need for refinement. Nevertheless, this work verifies a suitable system formulation methodology for a state-of-the-art fully-spatial dynamic interface simulation package for skid-equipped rotary-wing aircraft.