Federal Aviation Administration and National Transportation Safety Board personnel arrived in Honolulu on Thursday to investigate a near midair collision involving two commercial jetliners.

On April 25 an eastbound United Airlines Boeing 757 received an automated alert to avoid a westbound US Airways Boeing 757 about 200 miles northeast of Kona, the FAA said.

The planes were separated by eight miles laterally when the United crew responded to the Traffic Alert and Collision Avoidance System. On the next radar update 12 seconds later, the planes were separated by 5.3 miles laterally and 800 feet vertically, which was as close as they got to each other, according to preliminary radar data.

The required separation in that airspace is either five miles laterally or 1,000 feet vertically, according to the FAA.