Ageing aircraft not equipped with modern navigation equipment are likely to be allowed to use satellite navigation for basic area navigation (B-RNAV) after the January 1998 deadline for the introduction of B-RNAV in Europe.

A programme of work being carried out by Eurocontrol, and now almost complete, appears likely to establish that aircraft fitted with approved global-positioning-system (GPS) receivers will satisfy the performance criteria for B-RNAV. This will enable older aircraft and smaller general-aviation types to fly the more direct, fuel-saving routes being provided under the flexible-use-of-airspace plan, without their operators spending thousands of dollars on new, highly sophisticated, RNAV equipment. According to Richard Croft, of Eurocontrol's airspace division, the European Joint Aviation Authorities is "accepting the idea" that GPS can fit the bill for many operators - "-but only as a short-term solution to meet forthcoming RNAV requirements", he says.

Up to 20% of European airspace users are threatened with what amounts to expulsion from the B-RNAV air-traffic-services route network if they do not upgrade their avionics to meet the new Eurocontrol standards, which demand a navigation accuracy of 9km (5nm) on either side of the flight-track centreline. The installation of an approved GPS costs around $10,000.

"Tests so far show that there is no reason not to allow the use of GPS, provided that the existing ground-based aids remain for reversionary use," says Croft. Simulation trials has been carried out, in which "live" crews from British Airways have flown B-RNAV routes using GPS. The pilots showed that they were able to continue flying the B-RNAV route with little difficulty, using existing ground-based aids, after the GPS capability was deliberately degraded.

Eurocontrol has also looked at the case of GPS loss on a busy day, when congestion might limit air-traffic controllers' availability to assist aircraft suddenly dependent on radar and other ground-based aids to continue flying B-RNAV routes. "We identified few problems - most aircraft will be able to revert to conventional navigation quite easily," says Croft. Eurocontrol is "absolutely firm" on the B-RNAV deadline, he adds.

Source: Flight International