Thousands of travellers have had their flights cancelled because of a huge ash cloud from an erupting volcano in Iceland.
About 500 flights didn't take off across Europe on Tuesday - mainly in Scotland and north-east England in the UK.
There were fears that the ash could get caught in plane engines.
Weather experts can't tell how badly the cloud from the Grimsvotn volcano will affect flights on Wednesday.
Forecasters said changing wind patterns made it hard to predict the exact path of the cloud precisely.
Even President Barack Obama flew to London from the Republic of Ireland earlier than planned to avoid it.
Barcelona football players may also head to London on Tuesday to avoid missing Saturday's Champions League final.
The Grimsvotn volcano began erupting on Saturday with ash rising up to 20km in the air.
Lots of people are facing a long wait to see when flights their will take off
Last year, ash clouds from the Eyjafjallajokull volcano caused chaos for air travellers for a week.
The cloud disrupts aircraft travel because the ash can clog up and damage jet engines when it gets inside. It can also melt and block the ventilation holes, which means the engines can overheat and stop working.
Even though the ash is very fine, it can also damage the windscreen of an aeroplane.
For most people, the ash will not be dangerous at all, but sometimes fine ash can be bad for people who have breathing difficulties like asthma or lung diseases.
This map shows where the ash cloud is expected to travel