The Federal Bureau of Investigation (FBI) is reviewing more than 40 cases of unruly passengers on airlines across the country.

The US Federal Aviation Administration (FAA) referred 43 cases of people misbehaving on airplanes to the law enforcement agency during the past year.

The referred cases represent a small portion of airplane mayhem: there have been 1,375 unruly passenger reports made this year alone.

The rate of unruly passengers peaked in 2021 and has since dropped by over 80%, according to FAA data.

The two agencies adopted an information-sharing protocol in 2021 that allows the FAA to refer some cases to the FBI for review.

The partnership aims to ensure that unruly passengers face criminal prosecution when warranted.

During the height of the Covid-19, reports of such incidents surged, reaching a peak in 2021 with nearly 6,000 reports filed. That number included more than 4,000 incidents that involved airlines enforcing mask mandates aboard aircraft.

Since 2021, the FAA has referred more than 310 cases in total to the FBI.

Most incidents this year involved passengers exhibiting aggressive and threatening behaviour towards crew members and other passengers.

Among the referred cases:

• Three incidents where passengers attempted to breach the flight deck
• At least seven incidents where a passenger physically assaulted other passengers or crew members
• At least 13 cases of passengers exhibiting sexually inappropriate behaviour or sexually assaulting crew members or fellow passengers
• Four cases where passengers inappropriately touched or physically assaulted a minor passenger
• Two cases where passengers attempted to open exit doors or breach aircraft doors

The FAA pursues legal enforcement action against passengers who assault, threaten, intimidate or interfere with airline crewmembers.

The violations can carry civil penalties up to $37,000 (€33,200) per charge.

Last year, the FAA imposed $7.5m in fines after handling over 2,000 unruly passenger reports, with 512 investigations initiated.