A Malaysia Airlines plane has been missing since Saturday morning. A search is now on to try and find it.
It took off from Kuala Lumpur, the capital city of Malaysia, but contact with the plane was lost during the flight.
It's EXTREMELY rare for a plane to go missing like this.
But when it does the search can be very complicated. Expert Chris Yates explains the technology used in the search and challenges the teams face.
Planes, helicopters and ships from ten countries are all being used as part of the rescue operation.
The planes can fly over large areas of land and sea, looking out for the missing aeroplane.
Helicopters can cover a smaller area so if a closer look is needed somewhere, the helicopter can do this.
Ships are also used. They cover distance slower than planes but are helpful when search teams need to take a closer look at areas of the sea.
A large area is being searched, so the ships can share the task with the planes.
The search team are racing against time - the longer it takes to find a plane the wider the area becomes in which the plane may have drifted in the water.
Without knowing where the plane might be the area being searched is huge so it's taking a long time.
A plane going missing like this is extremely rare. Chris Yates says there are about 4 billion flight tickets sold every year in the world, so an incident like this is extremely rare.