When you see National Geography/ discovery MAYDAY programs, there are surprising facts about plane crashes.
We think that planes have backup systems. If one system does not work, then other will work. For example, if one engine fails, still pilots can use second one or if both fails, they can glide the plane to a suitable landing site.
However this is not always correct. There are critical parts in plane where there are no backups. For example, there are two parts at end of the plane, so that pilots use them to move up and down. If this part fails( indeed it happened in the past , they are frozen), the plane is doomed. This is a reality.