Mountain effects and the use of radio compasses and radio beacons for piloting aircraft

A report on tests made on the combined use of radio beacons and compasses by observations on board the flight research plane of United Air Lines, between Salt Lake City and Chicago. The theory of d.f. errors to be expected within a few wavelengths of the transmitter is considered carefully, and it is shown that, while these errors are of a similar nature whether the transmitter users a loop or an open aerial system, they are considerably worse for a loop. In particular, rapid changes in indicated direction are to lie expected as a plane passes over a station. These deductions are checked during the flight. On passing over the Rocky Mountains large and variable errors are found, due to reflections of the beacon beam, as was previously observed in the Alps. Some of the deductions are also tested with small-scale apparatus using u.h.f, transmission. The advantages of the beacon-compass combination lie in the greater ease with which a pilot can return to the beacon course after having deviated from it. It is considered improbable that the mountain effect would be reduced by using higher frequencies.