FROM time to time controversies arise as to the respective merits of two, or possibly more, solutions of a certain technical problem. These rage fiercely for a few years and then, usually, one system proves to be demonstrably better, and becomes almost universal. Thus the axial flow compressor is now universal for all but the smallest gas turbine aero‐engines. There is still an active discussion as to whether low‐voltage d.c. will be entirely superseded by 400 cycle a.c. At a recent conference on aircraft icing protection, mentioned in this issue, the relative merits of hot gas and electrical deicing were argued, as was the degree of automatic control which was desirable in a deicing system. In the field of aircraft auxiliary services the lead has for a long time been held by hydraulics, with electrical actuation challenging and pneumatics rather neglected, except for certain specialized applications. In an article in this issue Mr J. Wotton, of Hunting Aircraft, gives the findings of a project study on the possibilities of pneumatics, undertaken with the small twin jet airliner design known as the P 107 in mind.