Airspace Management

The reason Australia acquired two DME systems in the first place dates back to World War 2. Following successful development of military DME systems, the flourishing post-war commercial air transport industry saw a need for improved navigation aids. DME was discussed at the Montreal Provisional International Civil Aviation Organisation (PICAO) conference in 1947. The conference decided to recommend a 1000MHz DME as an international standard but member nations were left free to develop their own systems for internal use.

Australia queried the wisdom of standardising on a complex 1000MHz system and by the end of 1947 Amalgamated Wireless Australasia (AWA) had already started developing a 200MHz DME system in conjunction with the then Department of Civil Aviation (DCA) and CSIRO. In 1949, DCA awarded a contract for the supply of 95 dual beacon DMEs to AWA. By 1953 the world’s first commercial DME was operating. Unfortunately, AWA at the time did not look beyond its own shores in terms of offering the new technology to the rest of the world. Their focus was only on developing a system for Australia.

Meanwhile, DME research in the rest of the world was slow at first with the UK working on a similar 200MHz system in the early 1950s, but it did not enjoy commercial success. At around the same time, the US started work on a DME system to operate in the 950 to 1215MHz frequency range. This development led to the system we now know as the ICAO DME system or DME-N (N for Narrow Band).

Because of Australia’s unique system, aircraft operating in Australia requiring DME had to be retrofitted with DME-A avionics, also supplied by AWA. As international air transport expanded, more ICAO systems were put on line, requiring some Australian commercial aircraft to be fit with the DME-A as well as the new ICAO, or 1000MHz system. Australian international airports had to install DME beacons to cater for visiting foreign aircraft. So between the early 1960s, when the ICAO system came into being, and now, most Australian airports handling large commercial aircraft required both types of DME beacons and most Australian commercial aircraft carried two sets of DME receivers.

AWA ceased manufacturing DME-A in the late 60s due partly to the increasing use of the DME-N and commercial airlines not wanting the inconvenience of carrying duplicate avionics systems. In 1978, AWA started development on international DME and by 1985 had installed the first system at the privately owned airport at Argyle, Western Australia.

But the main motivation to abandon the 200MHz DME system was due to a 1991 Act of Parliament. The Spectrum Management Agency, which is responsible for allocating frequencies in the already congested airbands, effectively said they wanted aviation radio navigation broadcasting to vacate the 200MHz band. This was to make way for expansion of TV broadcasting frequency allocations.

The Agency, in its proposed Australian Radio Frequency Spectrum Plan of December 1994 said, “The allocation of the aeronautical radio navigation service will remain until existing services are transferred to other aeronautical bands. This transfer is to be completed by December 31 1995.”

The CAA points out that this exercise is not a case of reducing services or a cost cutting measure. “There was a legitimate reason why we had to free up the 200MHz band,” according to Noel Mara, Manager of the DME Transition Project. “It was out of the CAA’s hands.”

It seems a case of bad timing that the DME-A’s are withdrawn before GPS becomes fully operational. The CAA has started to address the problem by installing 30 DME-N beacons at some regional airports previously served by DME-A. However, some operators without DME-N avionics will find themselves operating into airports where there are only DME-N beacons or no beacons at all.

In a yet to be published circulation to pilots, the CAA forecast that DME-N is planned internationally to coexist with GPS as a navigation aid well into the next century.