Modern aeroplanes are for the most part 'flown' by autoflight computers. These computers can take over when the plane is just 30 metres off the ground, maintain whatever speed and height is tapped into the flight management system, and land the aircraft automatically. But when autoflight computers experience situations they haven't been programmed to handle – sudden structural damage to the aircraft, or extreme weather – they can throw back responsibility to the pilot, who may become confused over the level of control they have. The confusion is made worse by flight deck computers overloading pilots with a blizzard of alerts. This is when crashes are most likely to happen.