A Utah man was charged recently with carrying a weapon on an airplane and assault with a deadly weapon after he held a razor near the throat of the passenger sitting next to him on a Jet Blue flight from New York to Salt Lake City. He eventually surrendered the weapon, and nobody was injured. Still, in September, a passenger punched an American Airlines flight attendant in the back of the head during a flight from Mexico to Los Angeles.

Airline crews are facing far more of these kinds of incidents than before the COVID-19 pandemic. According to the Federal Aviation Administration, in 2019, there were 146 investigations into passenger unruliness on planes. However, as of November 1, there had already been 767 such investigations this year.

Should stopping such people be considered “vigilantism” — a term that conjures up visions of mob violence and lynching? Whatever we call it, few likely would question that under extreme circumstances, it still has a place. The Jet Blue and American incidents are tame compared to the passengers and crew of United Airlines Flight 93 fighting hijackers and causing the plane to crash in western Pennsylvania on Sept. 11, 2001.

There have been many incidents in which the actions of passengers, individually or working together, averted danger during commercial flights.

During a Paris-to-Miami flight, “shoe-bomber” Richard Reid unsuccessfully attempted to detonate explosives hidden in his shoes and was subdued by a flight attendant and a passenger; on a London-to-Washington flight, an apparently psychotic woman became unruly and had to be subdued and handcuffed by other passengers; a Nigerian terrorist tried to ignite an incendiary device as his flight was preparing to land in Detroit; and a flight attendant and two passengers intervened as a Yemeni national, shouting “Allāhu Akbar” (“God is Great”), attempted to break into the cockpit of a Chicago-to-San Francisco flight. In 2018, an agitated passenger on a St. Croix-to-Miami flight became combative after being denied more beer, scuffled with his seatmate, an off-duty policeman, and was arrested by the FBI after the plane landed.

For the millions of us who have begun to fly again, these incidents pose questions of when passengers should intervene and what they should do.

Tommy Hamilton, SWAT team commander for the police force at Dallas-Fort Worth Airport who has worked closely with air marshals, cautions against a rush to vigilantism and urges reliance on the professionals. “Federal air marshals have credentials and will identify themselves as soon as practical,” he said. “It will be easy to see who they are. They will not identify themselves until after someone has identified themselves as a terrorist-hijacker.”

But if no air marshals are aboard (and they are assigned to only about 5 percent of flights), flight attendants and passengers are the first lines of defense. Passengers should obey the directions of the flight crew, but they should be prepared, mentally and physically, to act. Like a basketball player getting ready for a jump ball, or a tennis player awaiting a serve, every able-bodied passenger needs to be ready to move, and to act aggressively, not tentatively.

Experts feel that only rarely will terrorists be able to get firearms or explosives on a plane, and having to rely on “softer” weapons puts them at a disadvantage when confronted by scores of passengers, who have at hand plenty of potential improvised weapons: a hard kick in the knee (easier to administer and more likely to succeed than in the groin, according to law enforcement officials); an elbow in the face or ribs; any sharp object in the eyes; a soda can torn in half, which yields a knife-like edge; a belt or computer cord used as a garrote; an oxygen canister (in one or more of the overhead bins) or metal coffee pot or wine bottle used as a club. (Go for the bridge of the nose or the temple, and swing for the fences: Remember that you’re dealing with a would-be mass murderer.)

Just as we need to be prepared for other rare but serious threats such as muggers or shooters in public places, when we fly, it’s important to maintain situational awareness and have a plan.