RENEWED US Federal Aviation Administration concern about military control of the global-positioning system (GPS) navigational-satellite constellation has been made public just as the GPS is to become the USA's primary means of civil-aviation navigation.

The FAA's disquiet is revealed in a letter to the US Air Force from Larry Stotts, the agency's avionics and navigation systems chief.

In an attempt to play down the matter, the FAA says that the USAF response to the letter is "-very positive", and that this is "-not the last word" on the subject.

GPS is the global navigation- satellite system which, according to White House-approved FAA policy, is to become the prime means of aviation navigation in the USA as soon as possible, with some terrestrial navigation aids already being "de-activated".

The letter reminds the USAF that the FAA will be activating its satellite-based wide-area augmentation system (WAAS) in "late 1998", adding that, "-civil aircraft will begin using the GPS WAAS as their primary means of navigation shortly thereafter".

Stott's letter to the vice-chief of the Air Force Space Command Lt Gen Patrick Caruana calls for "increased joint planning in certain areas of mutual interest".

The areas of emphasis include satellite-constellation sustainment, GPS/WAAS interoperability and co-location of the FAA's Satellite Navigation Center (SNC) with the USAF's equivalent GPS Master Control Station (MCS). The issue of Department of Defense control over GPS has always worried non-US aviation authorities and aircraft operators .

Caruana's letter rejected the co-location proposal out of hand, despite the FAA's offer to share costs. The FAA's SNC is to be at the US Naval Observatory in Washington, and Caruana says that the MCS will be at Vandenberg AFB, California. Caruana's reply confirms, however, that "-we fully intend to sustain the GPS constellation and provide a robust navigational signal to all users".


Source: Flight International