Even though they are usually continuously monitored, radio navigation aids need to be regularly checked in flght to make sure that they are radiating correctly. To accomplish this, DCA maintained a fleet of specialised Flight Survey aircraft: initially Douglas DC-3s and later Fokker F.27 Friendships.

During this period, the basic process for checking a navaid was for the survey aircraft to fly a series of pre-determined 'runs' using the aid for guidance. On the ground, Airways Surveyors would track the actual position of the aircraft using a theodolite set up at an accurately known position. While one Surveyor tracked the aircraft, another would use a VHF radio to relay the bearing (azimuth or elevation) to Airways Surveyors aboard the aircraft. The on-board Surveyors could then compare the true position of the aircraft, relayed from the ground, with the position according to the navaid as shown by the on-board instrumentation. These readings could be compared and, if the navaid was radiating incorrectly, the necessary adjustments could be calculated and relayed back to technicians on the ground.

Below: Airways Surveyors checking the new Runway 27 ILS at Melbourne/Tullamarine in about 1970, just before the airport opened. This is undoubtedly a posed photo as the DC-3 survey aircraft is well past the missed approach point and very low!

Above: The same processes continued into the F.27 era, in this case with the radio equipment stowed in a Departmental station wagon.

Left: Every navaid, no matter how remotely sited, needs regular flight checking. In this case a VOR beacon is being checked.