On Sunday, Greece's sky was closed. A strange noise stopped planes. This was a big problem. The people in charge said it was new. Loud noise made talking hard.
Controllers needed to talk. They acted fast. They kept planes safe. The problem started in the morning. It was a busy day for travel.
They did not find the noise's cause. People think it was a machine. Air traffic in Athens was less. Planes could not talk well.
So, flights changed paths. They did not fly over Greece. Flights took longer. Many people were late.
Experts looked for the noise. Teams checked machines. Talking was bad. So, fewer planes could fly.
Many flights were late. Some planes went back. Some flights went to other places. Many flights were very late. Travel was late all night.
Plane safety was okay. They used other ways. Later, more planes could fly. Flights started to be normal. They will find out why.