Climate change requires the reduction of energy consumption in transport and the associated fuel consumption, and emission of pollutants into the atmosphere. This issue is particularly relevant to air transport. Referring to the current legislative actions aimed at reducing the negative impact of air transport on the environment, the paper describes the possibilities of reducing energy consumption and related emissions. The Boeing 737 aircraft equipped with Snecma CFM 56C engines was adopted for the research. The research problem focused on determining a cruising trajectory characterized by the shortest cruising time and the lowest energy consumption by the aircraft during the flight between two selected European airports in given meteorological conditions. In the analysis, the Dijsktra’s algorithm was applied and built-in MATLAB functions were used. Based on the studied case, it was shown that it was possible to reduce both energy consumption and CO2 emissions by 10%. The novelty of the research described in the paper is the use of the energy approach and tying the energy parameters of the aircraft to the flight duration and pollutants emission in the cruise phase.