Flights into the Dallas area are being forced to take older, cumbersome routes and a runway at Dallas-Fort Worth International Airport has been closed after aviation authorities said GPS signals there aren’t reliable.

The Federal Aviation Administration said in an emailed statement Oct. 18 it’s investigating the possible jamming of the global-positioning system that aircraft increasingly use to guide them on more efficient routes and to runways. So far, the agency has found “no evidence of intentional interference,” it said.

American Airlines Group Inc., the primary carrier at DFW, said the GPS issue is not affecting its operations. Southwest Airlines Co., which flies from Love Field, didn’t immediately comment.

Despite the lack of flight disruptions, the GPS problem demonstrates the risks of widespread reliance on weak radio signals from space used for everything from timing stock trades to guiding jetliners.