FAA warns airlines of GPS outages due to secret naval tests

The Federal Aviation Administration (FAA) has warned pilots that GPS testing could leave the global-positioning signals ''unreliable or unavailable'' across much of the west for six days in June.

The testing got underway yesterday with its base in Southern California could affect the flight controls of a specific kind of business jet, the FAA warned. But experts point out that the testing should not affect commercial airliners.

''I think there are safeguards in place," said John Cox, a former airline pilot and now president of consulting firm Safety Operating Systems, USA Today reported.

He added that pilots and air-traffic controllers would keep an eye on planes within the warning area for any flight abnormalities. However, if pilots heard about strange GPS signals over radio in a given area, they could adjust altitude or navigate around the problem as if it were bad weather, he said.

''You route around it as if it were thunderstorms," Cox said.

The testing centered at Naval Air Warfare Center Weapons Division based in China Lake, California, could affect aircraft that were 50 feet off the ground up to a height of 40,000 feet above sea level and within hundreds of miles of the base to nearly 550 miles away.

The affected area would be shaped as upside-down layer cake, with the largest layer 40,000 feet high spanning California and Nevada, and stretching across much of Oregon, Idaho, Utah and Arizona.

The FAA has also warned pilots flying the Embraer Phenom 300, one of the world's most popular executive jet aircraft, that the testing could interfere with flight stability controls and added that extra care needed to be taken in the area.

The jamming would happen between 0930 and 1530 Pacific Time and more tests were planned. Further GPS jamming would happen around the same time on 9 June, 21 June, 23 June, 28 June and 30 June, bringing more disruption for travellers.

The US was not the only country carrying out the exercise.  The UK communications regulator Ofcom had issued an advisory that aircraft-based GPS jamming exercises would be held over the  Scottish Hebrides at 0900-1100 and 1300-1500 local time for the entire month of July.