However, due to high sensitivities of HLFC toward operational boundary conditions, estimations of its overall benefit are usually afflicted with large uncertainties. Among the critical environmental factors is the degradation of laminarity when flying through clouds at high altitudes. This paper provides an assessment on operational and economical effectiveness of HLFC aircraft with a detailed inclusion of the cloud encounter effect in three steps. First the expected time in cloud (TIC) in a real route network with cloud data given by the European Centre for Medium-Range Weather Forecast is analyzed, yielding an average TIC of 10%. Subsequently, HLFC fuel efficiency with and without considering the cloud effect on mid- to long-range aircraft is dealt with. Results show an average drop of fuel benefit from 12.8 to 12.0% due to clouds. The effectiveness of lateral route optimization to reduce the impact of clouds is investigated in the last analysis. Outcomes show that these mitigation strategies are economically beneficial for few cases only. The overall picture confirms that cloud encounter must not be neglected when assessing aircraft with HLFC.
