Honeywell believes that a failure to approve the global positioning system (GPS) for sole means use because of concerns over jamming will not harm the long-term market prospects for its satellite landing system (SLS).

The company says improved versions of the SLS, now under development, will overcome problems with signal interference and will be capable of improving the accuracy and availability of GPS over a wider area, possibly allowing its approval for sole-means use.

The company achieved a milestone in the protracted development of its SLS on 21 September, when Continental Airlines completed the first commercial flights to use a certificated differential GPS (DGPS) landing system.

Continental flight 9980, using a Boeing MD-83, performed DGPS precision approaches at New York Newark and Minneapolis St Paul airports, which are equipped with Honeywell/Pelorus SLS-2000 ground stations.

Both units are so-called "private-use" Special Category I systems approved for Continental only. The MD-83 is the airline's sole DGPS-approved aircraft, and will be used for in-service evaluation.

Honeywell is developing an improved "public-use" Category I SLS, or local area augmentation system (LAAS), scheduled to be certificated in 1999. This will be followed by a next-generation Cat I LAAS with improved accuracy, which will form the basis of a Cat 3 all-weather DGPS landing system.

Company officials believe it will be "seven to 10 years" before the SLS/LAAS is ready to replace the instrument landing system (ILS). GPS has come under fire because of the ease with which the low-power satellite signals can be jammed, but the officials argue that ILS signals can be easily "spoofed" - which is potentially more dangerous, they say - and that has not prevented the system becoming the international standard.

Source: Flight International