The photo above shows the Laser Tracker airways survey equipment set up at Cairns, Qld., for an inspection of the Instrument Landing System (ILS). This equipment was introduced in 1997 for use with Airservices Australia's new Astra VH-FIS and Super King Air VH-FIX.

The entire system comprises, from left to right: a differential GPS antenna for correcting GPS position errors; several datalink antennas to up- and down-link data between the tracker and the aircraft; the Laser Tracker itself on the tripod with hand terminal resting at base; and boxes containing the datalink electronics.

The Laser Tracker is a form of theodolite which locks on to and tracks a laser reflector on the belly of the aircraft. The relative position of the aircraft from the tracker can thus be accurately determined.

This system is completely automated and does not require a surveyor on the ground once set up, thus providing considerable manpower and cost savings. Unlike the previously-used Optical Tracker, the system is capable of tracking in elevation and azimuth simultaneously, also providing savings in the number of runs to calibrate an ILS.

Also, the Laser Tracker is only used for the calibration of ILS, T-VASIS and PAPI - all other navigation aids are calibrated using GPS position reference data alone.