Heathrow's Terminal 3 suffered a whole host of IT glitches yesterday, which delayed up to 6,000 passengers.
The software glitch meant that all information about incoming and outcoming flights failed to display on the terminal's computer screens, resulting in passengers being prevented from entering the building.
Although the IT glitch only lasted for an hour, it did mean that the world's biggest airport had to cancel two flights and delay many more.
It also meant that checking-in was slower than normal and that some bags were actually put on the wrong flight.
Heathrow has been plagued with IT problems ever since it opened Terminal 5. The problems at the new terminal were so bad that the company had to launch an advertising campaign that used up-to-date images of the terminal functioning properly to prove to customers that all is working as it should.