The Federal Aviation Administration is warning 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 that began Tuesday based in Southern California could hurt flight controls for a specific kind of business jet, the FAA warned. But the testing shouldn’t affect commercial airliners, according to experts.

“I think there are safeguards in place,” said John Cox, a former airline pilot and now president of consulting firm Safety Operating Systems.

Pilots and air-traffic controllers will keep an eye on planes within the warning area for any flight abnormalities, he said. But if pilots hear by radio about strange GPS signals in a given area, they could adjust altitude or navigate around the problem as if it were bad weather, he said.