Q&A: Why some planes are crowded even with air travel down

Every once in a while, social media lights up with photos or video from flights that are nearly full, with passengers clearly violating advice from public health officials about social distancing during the coronavirus pandemic.

That raises the question: How can planes still be full when air travel is down more than 90% from a year ago?

In some cases, airlines are creating the crowds by canceling other flights and packing passengers on the few remaining planes. Carriers say, however, 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.

Here are some questions and answers about flying during the coronavirus pandemic.

HOW MANY PEOPLE ARE STILL FLYING?

The number of people traveling on airlines is scraping along at levels not seen in decades, and there are only about 17 passengers on the average domestic flight. But that’s just an average.

The number of people passing through airport security checkpoints has been rising since mid-April, but it is still down 93% from a year ago. The Transportation Security Administration screened 163,692 people on Monday, compared with nearly 2.5 million on the comparable day a year ago.

SO WHY ARE SOME FLIGHTS FULL?

Partly it is due to the high number of canceled flights.

“On routes where there used to be scores of flights between the different carriers, now there may be two or three,” says Robert Mann, a former airline executive and now a consultant in the New York area.

Airlines slash their flight schedules, and then they cancel even more flights in the last few days before departure. That can force passengers who were...