Probabilistic modelling of LORAN-C for non-precision approaches

Abstract

A mathematical model of the expected position errors encountered from LORAN-C during a non precision approach was formulated. From this, position error ellipses were generated that corresponded to two time difference correction schemes. One involved relaying corrections to the pilot just before he initiated the approach, and the other involved publishing time difference corrections in the instrument approach plates. It was found that the errors associated with both update scenarios were well within FAA AC90-45A accuracy standards for non precision approaches. The former scenario showed a significant improvement over the latter. Flight tests were conducted in a general aviation airplane carrying an equipment test bed designed to take data from a LORAN-C receiver and an ILS localizer receiver. The results of the flight tests show that the LORAN-C had a maximum error (average plus one standard deviation) of 1.276 degrees deviation from the localizer path, and an average error (average plus one standard deviation) of .648 degrees. It is concluded that LORAN-C is a suitable navigation system for non precision approaches and that time difference corrections made every eight weeks in the instrument approach plates will produce acceptable errors.