A proposal of a precise distance measuring system which counts the number of phase cycles of a radio wave transmitted by an airplane employed for flight test. The objective of the study is to analyze the accuracy of the measurement of the distance between the ground station and the plane which usually flies quite closely to the station and at low altitude.

The system employs two crystal oscillators having a stability of about 10^-10 per hour, one at the station, the other in a plane and they are synchronized each other. Therefore, the distance is measured by counting phase cycle of the radio wave, purely sinusoidal one in 30MHz band.

Since the multipath phenomenon is the most important factor for the range determination accuracy, the influence is studied and evaluated.

The received signal is cross correlated with the synchronized signal, the output of synchronized oscillator.

The study indicates an error less than 0.1% can be expected for the system even in the worst circumference.

One of the most important things in carrying out a flight experiment on navigation is to determine the aircraft position accurately and keep her track continuously.

This report describes needs of aircraft positioning methods in the first part and then presents technical data obtained by use of TACAN signals, both on the ground and in the air.

In the first section, a thought was given to the fact of received signals composed of rapidly and slowly fluctuating radiated signals, and a method to discriminate these two.

In the following section, an antenna design is described with data obtained on the ground.

Then, an aircraft positioning method using the antenna and TACAN signals is stated.

A radio navigation overall performance is governed by its signal qualities in the air between aircraft and the ground station.

And the data obtained thusfar clearly show this fact.

However, we could not prove this theoretically yet.

An Evaluation test on the navigation accuracy of an RNAV (Area Navigation) system, using the Lock-heed L-1011, was carried out by the Electronic Navigation Research Institute in collaboration with All Nippon Airways and the Japan Civil Aviation Bureau in November 1974. This paper deals with the method and the result of this flight test on the evidence of traces obtained with the automatic photographic radar recorder set up on the CRT display of the airport surveillance radar at Tokyo International Airport.

The cross track errors of the aircraft are calculated as a measure of the navigation accuracy on the basis of the data taken by the method mentioned above and we compared them with the FAA RNAV criterion, Advisory Circular AC90-45A. The result with some assumptions shows that the cross track errors are within the tolerance mentioned above.