ATLANTA (AP) — Delta Air Lines said Thursday that it has completed upgrading its fleet to protect key equipment against interference from 5G wireless signals, plugging a hole that could have disrupted flights during low visibility.

The airline said all its planes in active use now have radio altimeters that are protected against interference.

“This means no Delta aircraft will be subject to additional weather-driven constraints,” a Delta spokesman said.

In late June, 190 of Delta's roughly 900 planes lacked the upgraded altimeters. Those devices use radio signals to precisely measure the height of a plane above the ground.

The issue forced Delta to consider rerouting those planes to avoid low-visibility situations while it waited for new parts from a supplier, although the airline said Thursday that it got through summer without notable problems with altimeters.

Transportation Secretary Pete Buttigieg pushed airlines to retrofit planes before the summer travel season, and most did. Among the largest U.S. carriers, only Atlanta-based Delta missed a July 1 deadline to upgrade all altimeters before AT&T, Verizon and other wireless carriers boosted the power of their C-Band, 5G signals. Flight disruptions, which some had expressed concern about, didn’t materialize, however.

Some aviation experts and the Federal Aviation Administration believe that C-Band signals are too close to frequencies used by radio altimeters. The Federal Communications Commission, which granted 5G licenses to the wireless companies, has said there is no risk of interference.