The aviation industry has set ambitious emission reduction targets for 2050. Following the success of electrification in the automotive industry, the potential of hybrid electric propulsion (HEP) has been the subject of many scientific projects. The energy and power of the electric systems that support the aircraft propulsion system are typically applied during the energy-intensive take-off and climb phases of the flight. This results in a considerable mass penalty for the remainder of the mission. An all-electric unmanned aerial vehicle, which decouples from the main aircraft at the cruise altitude and returns the electric propulsive system to the departure airport, could thus allow to limit the environmental footprint of a particular flight. The present study has quantified the potential fuel, energy and emission reductions of an Airbus A320neo assisted by such an auxiliary aircraft. This potential is also compared to a parallel-hybrid A320neo entering into service in 2035. The required modelling and mission evaluations have been performed with the MATLAB-based integrated simulation framework ‘Mission, Aircraft and System Simulation’ (MASS). The mission, aircraft and engine models of this tool, developed at the Royal Netherlands Aerospace Centre (NLR) throughout multiple HEP studies, have been modified. Besides, constraints for engine temperatures and shaft speeds have been applied. For the 3,500 nautical miles (6,482 kilometres) design mission, fuel and energy reductions of about four and two and a half per cent are found respectively. For the 850 nautical miles (1,574.2 kilometres) standard mission, a fuel reduction of about five per cent can be achieved. The overall energy demand increases slightly in comparison with the reference Airbus A320neo. No feasible parallel hybrid-electric design point was identified for these two mission profiles. In order to account for the uncertainty inherent to a preliminary design stage, the impact of multiple model parameter variations is assessed in a design study. In the vast majority of the investigated scenarios, single digit fuel and emissions savings can still be realised with this innovative aircraft architecture. A more detailed aerodynamic analysis and further refinement of the propulsive system model are recommended subjects for subsequent research.