Investigators from the US National Transportation Safety Board (NTSB) are investigating a 27 March near-miss over San Francisco involving a United Airlines Boeing 777 and a small light aircraft.
The NTSB says that the crew of United flight 889 operating N216UA destined for Beijing was cleared for takeoff from runway 28L at San Francisco International airport to climb to an initial altitude of 3,000ft (915m).
The first officer, who was flying the 777, reported that after the landing gear retracted and the jet was at an altitude of 1,000ft, the tower reported traffic at his 1 o'clock position.
Immediately after the controller's traffic advisory, the 777's traffic collision avoidance system (TCAS) issued an audible traffic alert. The United pilots saw an Aeronca 11AC light high wing aircraft in hard left turn "travelling from their 1 o'clock to 3 o'clock position", says NTSB.
The first officer then pushed the control column to level the aircraft, and both crewmembers only reported seeing the underside of the Aeronca as it passed within an estimated 200ft-300ft (61m-91.5m) within the 777.
The TCAS then issued an "adjust vertical speed alert" followed by a descent alert. The first officer complied and flight 889 continued to Beijing without incident.