THE US FEDERAL Aviation Administration has completed flight-tests to determine the feasibility of Category IIIb automatic landings using the global-positioning system (GPS). Results from flight-tests by E-Systems and Wilcox, in June and April, respectively, are being analysed. The results are expected to be released by September.
The tests will determine which differential-GPS (DGPS) technique the FAA selects for the local-area augmentation system (LAAS), which will increase GPS accuracy, availability and integrity to the levels required for Cat II and III precision approaches.
The Wilcox tests, using a FedEx Boeing 727-200, evaluated a narrow-correlator code-tracking GPS receiver, while the E-Systems tests, using an Israel Aircraft Industries Westwind II, involved more accurate, but more complex, kinematic carrier-phase tracking.
Wilcox believes that the tests "...successfully showed that the DGPS code processing can be used for Cat III precision approaches and landing". E-Systems says that the results from its flight trials "...appear to be promising. It is likely we passed the FAA's test."
The FAA is expected to select a LAAS technology in 1996. The agency is also evaluating a ground-based "pseudolite" (pseudo-satellite) DGPS technique developed by Stanford University which eliminates the need for a ground-to-air datalink to carry the differential corrections.
E-Systems' Montek division and Wilcox Electric are among companies which have responded to a request for proposals for LAAS engineering-support services. This is intended to pre-qualify four teams to compete for future LAAS contracts. The teams had to propose LAAS architectures as the major part of their bids. The award is expected this year.
The FAA plans to provide Cat I capability using the wide-area augmentation system (WAAS), which will broadcast integrity data and differential corrections. Wilcox has been selected to develop the WAAS.
There is widespread scepticism that the WAAS will be operational as planned in 1997 and provide Cat I capability by 1998. Many consider the year 2000 a more likely date.
Source: Flight International
