The Singapore Airlines incident this week that left one person dead and dozens injured after hitting turbulence has highlighted the risks that can come when your plane flies through such rough air. Experts say turbulence can be caused by various factors like storms or flying over mountain ranges, but one of the most dangerous is known as "clear-air turbulence" because there's no way to know if you are going to fly into it. As Sean Previl explains, there are ways air travellers can stay safe and it takes one simple step, even if it may seem obvious.