COMBINED GLOBAL-positioning-system (GPS)/Russian Glonass receivers can significantly boost the integrity of real-time satellite-based differential-navigation systems in aircraft, says a UK team which recently completed what are believed to be the world's first flight trials of such a system.
The UK Civil Aviation Authority's Institute of Satellite Navigation (ISN), which performed the tests using a UK Defence Research Agency BAC One-Eleven, found that "-the availability of a large number of satellites-will improve integrity during each phase of flight".
Most civil satellite-navigation systems use signals from the US GPS satellite constellation, the accuracy of which is deliberately degraded for security reasons. Differential GPS (DGPS), meanwhile, introduces ground stations which transmit corrections to the satellite data, and is accurate enough to allow pilots to make precision approaches. The problem is that there may not always be an adequate number of GPS satellites available to allow DGPS to be relied upon as a sole means of navigation.
The combined GPS/Glonass receiver effectively doubles the number of available satellites, with the additional benefit that the Russian Glonass receivers are not degraded.
The ISN experiment found that combined GPS/Glonass availability never fell below ten satellites, while GPS-only availability could fall as low as four.
Most industry experts, believe that absolute integrity can only be achieved, with a minimum of six satellites in operation.
Source: Flight International
