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Before ICAO's CNS/ATM system has even reached implementation, there are warning signs that it could be saddled with a compromise patchwork of systems because it does not have the flexibility to adapt significant advances in technology that have emerged since the plan was approved in 1991.

As a result, periphery technology such at TCAS (the US traffic collision and avoidance system) and ACAS (the more generic aircraft collision and avoidance system) -is being tagged onto the formally defined CNS/ATM as something of an afterthought.

It is, acknowledges Air Navigation Bureau Director William Fromme, a somewhat back-to-front approach, especially when there is already a system available which inherently incorporates virtually all the elements of the CNS/ATM system, which are currently being developed on a piecemeal individual basis.

That system is the GPS transponder developed by Swedish scientist Hakan Lans, whose past credits include the computer mouse and colour computer graphics. Lans believes that his system can replace all existing ground-based navaids, as well as providing a data link, a precision approach capability, and collision avoidance in the air and on the ground. By relying on the fourth dimension - time - as its foundation, the GPS transponder also has the potential to operate as a satellite back-up system, allowing the global network to continue functioning - albeit with reduced levels of accuracy - in the unlikely event of a total satellite failure.

Fromrne acknowledges that the Swedish system "is technically an extremely interesting proposal" but suggests ft may be ahead of its time.

"The Swedish GPS transponder/TDMA (self-organising time division multiplex) is essentially an ATC system - much more than a simple communications system," Fromme told ATC NEWS. "But it is a departure from what was endorsed at the 10th Air Navigation Conference In 1991. I'm sure that Sweden is surprised and probably disappointed that there hasn’t be more enthusiasm in the rest of the industry for what is doing. But this is new technology and maybe it takes longer for new technology to win acceptance. After all. it was 1988 when the Future Air Navigation System (FANS) was first proposed to ICAO, that was seven year ago. It has been four years since the 10th Air Navigation Conference and look how long it has taken us to got this far." The Swedish system uses GPS time referencing which Fromme says "is more accurate than any other time referencing global system that is available." The more accurate the time reference, the more efficient the use of the frequency spectrum. It allows for a great deal of information to be channelled into the system at the same time very efficiently.

"It is a little bit back to front to patch systems like TCAS into the system as they emerge, but the reality in that we already have TCAS specifications; we don't yet have any for the GPS transponder. However, when we move on to ACAS III or TCAS IV, which use the GPS for horizontal separation monitoring, then it is going to be difficult to answer the question why we are doing it this way when we already have a GPS transponder that does ACAS plus a great deal more. I'm glad I'm not going to have answer that question myself."

Fromme steps down from his eight year term in office as head of the Air Navigation Bureau In August this year.