The system for keeping peace in America's skies is creaking under the pressure of what airlines and regulators say is an unprecedented proliferation of misbehaviour. The Federal Aviation Administration has received more than 3400 reports of "unruly" passengers this year. But despite launching a "zero-tolerance" enforcement policy in January - amid a rise in conflicts often tied to mask requirements in the air - the agency said that as of mid-July it had "completely closed" just seven cases. The sprawling, multi-tiered system for enforcing regulations and federal laws covering passengers can take years to play out. As travel rebounds, that structure is being strained by confrontations fuelled by alcohol, hostility to mask mandates and small conflicts that careen out of control. One passenger hit a woman holding an infant amid an apparent dispute over a window shade. Another ran through business class and stomped on a flight attendant's foot after the power outlet at her seat wouldn't charge her phone, according to court records.