The search continues for an aeroplane that has been missing since 8 March.
The plane was flying from Kuala Lumpur, in Malaysia, to China's capital, Beijing when contact was lost.
All week authorities have been searching for it, but no one yet knows exactly what happened. People are puzzled because it is extremely rare for something like this to happen
One thing we do know is that Flight MH370 left Kuala Lumpur International Airport on Friday afternoon (British time), and was due to arrive in Beijing six hours later.
The last contact air traffic controllers had with the plane was about an hour into the flight when it reached the boundary between Malaysia and Vietnam.
Authorities think it's unlikely that anyone survived and teams from around the world, including 42 ships and 39 aircrafts, are searching the sea for the plane.
Early search efforts focussed on waters between Malaysia and Vietnam, but it was expanded to an area off Malaysia's west coast after Malaysian authorities reported that the plane could have turned back.
On Wednesday, the search was widened again, to the Andaman Sea.
A search this scale is very difficult because the teams have hundreds of square miles to cover and there are differing reports about the plane's last location.
Doubts have been raised about how the search was carried out at first, and lots of different theories have been put forward about what may have happened to the plane.
For now, it remains a mystery.
An incident like this is extremely rare, if you're upset about anything you've seen in the news, take a look at our guide.