The Federal Aviation Administration is investigating the circumstances that led a Nassau County police helicopter to fly low above a large crowd last week at Jones Beach in order to disperse the gathering.

State parks and Nassau police had responded to the scene at Jones Beach late Thursday to break up a beach party advertised online.

A Nassau police helicopter flew above the large group, hovering low over the crowd, before circling back as other law enforcement arrived to disperse about 500 mostly high school and college students on the beach.

On Monday, Nassau County Police Det. Lt. Scott Skrynecki said: "We are fully cooperating with the FAA inquiry."

An FAA rule requires that "no pilot may operate an aircraft below an altitude where, if the engine fails, an emergency landing cannot be made without creating an undue hazard to people or property on the surface."

The rule applies to all aircraft, including law enforcement, except for takeoffs and landings.

FAA officials said Monday that all aircraft, including helicopters must maintain a minimum altitude of 1,000 feet over congested areas "above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft."

Aircraft must maintain a minimum of 500 feet over other areas "except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure."

Helicopters can fly at lower elevations, "provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA."

Nassau police said they responded to fighting on the beach that left four people with minor injuries before the crowd dispersed. Police also arrested a Valley Stream man who officers said raised his shirt to show what appeared to be a gun in his waistband. The crowd was cleared by 8 p.m.

Nassau County Executive Bruce Blakeman defended police efforts to break up the gathering.

"We are confident the actions taken by the NCPD aviation helicopter were instrumental in dispersing a large crowd of individuals who were engaged in fighting and other disruptive behaviors, thereby saving our kids from getting hurt," Blakeman said.