Every once in a while, pictures or videos of airplanes nearly full of passengers appear on social media. That seems to violate advice from public health officials related to social distancing during the coronavirus crisis. Some people have raised the question: How can airplanes still be full when air travel has decreased more than 90 percent from a year ago? In some cases, airlines are creating the crowds. They are canceling flights. Passengers must then crowd onto the few remaining planes. The airlines, however, say that they are taking action to ease passengers’ fears about coronavirus contagion. Some are blocking middle seats or letting passengers pay extra to guarantee an empty seat next to them. They are also starting to require passengers to wear facial coverings.