Fewer passengers became unruly on commercial flights last year but more of those incidents involved serious behavior problems such as fighting or threatening passengers and crew members, an airline trade group said.
The International Air Transport Association categorizes the incidents on a scale of 1 to 4, ranging in severity from a passenger who does not comply with safety procedures to one who attacks the cockpit crew.
The overall number of unruly passenger reports decreased slightly more than 9 percent to 9,837 last year from 2015, the trade group said. Most of those cases, 87 percent, were considered the least severe, or level 1 incidents, the report said.
But the share of incidents considered level two cases _ involving "physical aggression to others and damage to aircraft" _ rose last year to 12 percent, up from 11 percent in 2015, the trade group reported.
Also, the number of cases in which the cabin crew had to restrain a passenger rose 169 last year from 113 in 2015.
Alcohol played a role in a third of the level 2incidents, the report said.
The trade group said most of the drinking took place at airport bars and restaurants or in the plane without the knowledge of the crew. The trade group urged bar and restaurant operators to train employees to avoid serving too much booze to passengers who are about to board planes.
It also called on more countries to ratify an agreement to impose harsher punishments on misbehaving passengers.
"Too often those accused of unruly and disruptive behavior are often released without charge," the report said.
