The U.S. Air Force on Wednesday canceled more than a dozen training flights in Britain due to the ash cloud from an Iceland volcano that has disrupted commercial aviation in parts of Europe since Tuesday.

The fighter jet sorties were halted as a safety precaution, said 3rd Air Force spokesman Lt. Col. Dave Honchul. Required missions were flown as scheduled, and there was no impact to flight operations at Ramstein Air Base, the military’s busiest hub in Europe.

Airports in northern Germany, after shuttering early Wednesday, opened again Wednesday afternoon as the ash cloud dissipated and volcanic activity ebbed.

European airspace was expected to return to normal Thursday.