The US National Transportation Safety Board (NTSB) says it is investigating an operational error that resulted in two American Airlines jets coming within a half-mile of each other horizontally as they approached parallel runways at the Chicago O'Hare International Airport in visual weather conditions on the afternoon of 1 June.

Due to an "air traffic control oversight", NTSB says Flight 879, an MD-82, while being vectored overshot the final approach course for runway 28 and continued northbound, "conflicting" with Flight 93, a Boeing 767 on final approach to runway 27L.

"According to preliminary Federal Aviation Administration data, lateral separation decreased to 0.35 nautical mile (1.2km) and vertical separation was 0 feet before the conflict was resolved," says the NSTB, adding that there were no injuries or damages reported.

Weather conditions were good at the time of the incident, with a cloud ceiling of 1,676m (5,500ft) and visibility of 8.7nm (10mi), says the NTSB.

Source: Air Transport Intelligence news