Airports in Northern Ireland and parts of Scotland were closed on Monday because of more volcanic ash cloud from the Icelandic volcano Eyjafjallajokull.
Heathrow and Gatwick airports were shut but have now been reopened.
The people who monitor flights are keeping a close eye on things in case the cloud changes direction again.
The volcano caused six days of travel chaos in April, and again last week which has caused huge travel problems for hundreds of thousands of Brits.
At the moment the no fly zone over the UK is affecting airports including Belfast City, Londonderry, Kirkwall and Stornoway.
Transport experts around Europe have been meeting to discuss ways to avoid the problems caused by the cloud last month.
There are worries that the volcano will keep erupting for a long time, and more trouble could be on the way.