The operation of helicopters in all weathers is an essential development if full advantage is to be taken of this class of vertical take-off aircraft. Helicopters must operate in weather minima at least as low as the current fixed-wing limits of 300 yards visibility and 300 ft. cloudbase, and should approach the limits approached by surface transport which continues to operate down to visibilities of the order of 10 to 20 yards. Present experience suggests that it should be possible to conduct regular operations down to 200 yards visibility and 200 ft. cloudbase provided the necessary aids are available. As experience is gained, these limits might be reduced to 150 yards and 150 ft. However, as the pilot needs time to change over to visual guidance before landing, it does not seem likely that these limits could be much reduced before the development and acceptance by civil operators of either completely automatic landing or some radical new landing aid.