At present the rate of failure of a weather radar set is of the order of 1 failure in 50 sector flights. Probably the most reliable unit of the equipment is the scanner, which is fortunate because it is the most difficult unit to locate in an aircraft by virtue of its size and the need for uninterrupted forward scanning. With its present size the installation of two scanners is not feasible. In a piston-engined aircraft a radar failure when confronted by prolonged turbulent cloud conditions means no loss of aircraft range due to the adoption of optimum turbulence airspeed. The serviceability rate afforded by a single equipment is, therefore, acceptable since speed is not critical to performance. In a jet the inability to pick a way around turbulent cells if the radar fails, necessitates, by the adoption of optimum turbulence airspeed and altitude, a considerable shortening of range. It may be that in a supersonic aircraft, an unserviceable weather radar will make the flight abortive, since the ability to become supersonic will depend on smooth flying conditions.

The choice of airspeed and altitude have a far more critical effect on economy of operation throughout the flight of turbo-jet aircraft than with the piston-engined type. The method of operating piston-engined aircraft for maximum range is well known, though it is normally only used on very long stages when fuel is critical; generally constant-power or constant-airspeed cruising, which result in a small penalty of fuel or payload, are preferred. The choice of operating height is also fairly wide within certain obvious limits. With jet aircraft, however, airspeed and operating height become critical and variations from economic operation reduce the payload or range considerably. The preparation of the flight plan, involving the choice of cruising altitude and speed, therefore becomes of major importance to the jet operator and navigator. The guidance of the aircraft's flight path in the vertical plane, in other words, takes on a new significance and affects the navigator's task both in planning and in flight.

The Nauticator is a vectorial computer for the solution of spherical trigonometrical problems, designed by Captain Leiv Jernæs of the Royal Norwegian Navy, who is at present captain of the training ship M.S. Sjöveien, Oslo. The instrument has been designed particularly for the rapid reduction of astronomical sights, and the calculation of great-circle tracks, distances and vertices. It has been sent to the Institute to assess its value, and this note will discuss its value to the air navigator.