A military helicopter crossed in front of a United Airlines flight from San Francisco to Santa Ana, California, as the plane was coming in to land at John Wayne Airport in Santa Ana. The incident occurred around 8:40 p.m. local time on Tuesday. The pilots were advised by the Sikorsky Black Hawk helicopter during final approach and received a traffic alert, which they responded to by leveling the aircraft. The two aircraft were separated by 525 feet vertically and only 1,422.43 feet or 0.27 miles when the helicopter crossed into the United plane. The California National Guard confirmed that the helicopter was returning from a routine training mission and landed safely. The Federal Aviation Administration is investigating whether a new measure to suspend the use of visual separation between airplanes and helicopters was applied.