Report shows satellites are blockable

WASHINGTON - The satellite system that the Federal Aviation Administration is counting on to help planes arrive on time can be blocked or jammed, a new government report says.

The report by the Transportation Department's Volpe National Transportation Systems Center said that the signal from the satellites, known as GPS or Global Positioning System, could be blocked by buildings or interference from other transmissions.

In addition, the signals could be jammed or the satellites could be attacked, though the report calls the last scenario "highly unlikely."

The report warned: "As GPS further penetrates into the civil infrastructure, it becomes a tempting target that could be exploited by individuals, groups or countries hostile to the United States."

The use of the satellites is part of the FAA's $11.5 billion plan to allow more planes to land, take off and fly from place to place.