Experiments in the determination of VOR radial stability

Results of recording VOR course deviation indicator (CDI) position at a fixed point 40 miles from the transmitter are presented. Traces show CDI deflections are frequently greater than one degree; wave interference phenomena and temperature inversion effects are suggested as possible causes for two of four general types of deviations identified (impulse and drift). Many significant CDI deviations for which no causes have been identified have been observed over a nine-month period.