Is it safe to fly with the threat of COVID-19 all around us? A new study from the Department of Defense shows it’s very hard to contract COVID-19 on an airplane. The researchers observed you would have to sit on the same plane with an infected passenger for 54 straight hours before you inhaled enough viral particles to become infected. While that finding is surprising, in some ways, it makes sense. The ventilation systems on modern airplanes recirculate air through filters that remove particles much quicker than in our homes. And cabin air is continually pressed down, making it difficult for an infected droplet to settle on a surface like an armrest.