Since it was disclosed late last month that President Bush has directed the Department of Defense to draw up plans for temporarily disabling the U.S. network of GPS satellites during a national crisis to prevent terrorists from using the technology, operators have been seeking more details and clarification of the policy. How U.S. policy would apply to Galileo, Europe’s planned GPS network, is unknown. How such plans would affect air navigation in the U.S. is not entirely clear, but the existing network of ground navaids is sufficient to keep traffic flowing despite aviation’s increasing reliance on GPS.