Joint Authorities for Rulemaking of Unmanned Systems (JARUS), ECTL_ATM CONOPS, Doc. JAR-DEL-SEC-01, First edition, Draft, 26/06/2017.
 International Civil Aviation Organization (ICAO), Safety management manual, Doc. 9854_AN/458, Montreal (Canada), 2013.
 European Aviation Safety Agency (EASA), Notice for Proposed Amendment (NPA), 2017.
 International Civil Aviation Organization (ICAO), Global air management operational concept, Doc. 10019_AN/474, Montreal (Canada), First edition, 2005.
 https://www.nasa.gov/centers/ames/greenspace/ green-aviation.html, accessed on 19/10/2017.
 EUROCONTROL Experimental Center, GAES project: potential benefits of fuel cell. Usage in the aviation context, EEC/SEE/2006/004, European Organisation for the Safety of Air Navigation EUROCONTROL, 2006.
 J. Sliwinski, A. Gardi, M. Marino, R. Sabatini, Hybrid-electric propulsion integration in unmanned aircraft, Energy, 2017.
 N. Sammes, Fuel cell technology reaching towards commercialization, Springer, 2006.
 K. P. Valavanis, G. J. Vachtsevanos, Handbook of Unmanned Aerial Vehicles, Springer, 2015.
 https://en.wikipedia.org/wiki/Unmanned_aerial _vehicle, accessed on the 27/10/2017.
 M. Colucci, Electric propulsion for sports use (Propulsione elettrica per uso sportive), Master Degree thesis, Politecnico di Torino, 2013.
 S. Leutenegger, C. Hürzeler, A. K. Stowers, K. Alexis, M. W. Achtelik, D. Lentink, P. Y. Oh, R. Siegwart, Flying robots, Springer handbook of robotics, Springer, 2016, pp. 623-670.
 SAE international, Innovative all-electric motor glider project, 2012. http://papers.sae.org/2013- 01-2114/
 J. Höflinger, P. Hofmann, Thermal management of a fuel cell range-extended electric vehicle, Springer, 2017. DOI 10.1007/978-3-658-19224- 2_7
 J. Töpler, J. Lehmann, Hydrogen and fuel cell technologies and market perspectives, Springer, 2016. DOI 10.1007/978-3-662-44972-1
 P. Osenar, J. Sisco, C. Reid, Advanced propulsion for small Unmanned Aerial Vehicles, The role of fuel cell based energy systems for commercial UAVs, BALLARD WHITE PAPER, 2017.
 D. Verstraete, A. Gong, D. D. C. Lu, J. L. Palmer, Experimental investigation of the role of the battery in the AeroStack hybrid, fuelcell- based propulsion system for small unmanned aircraft systems, International Journal of Hydrogen Energy, Vol.40, No.3, 2015, pp. 1598-1606.