According to media reports, the Beijing-bound United Airlines Flight 889 had just taken off and was at 1,100 feet when the tower alerted the pilots that another plane was in the same airspace. The crew reported seeing the Aeronca 11AC bank hard left and head towards UA Boeing 777 at great speed.
As a result of the air traffic controller's warning, the Boeing collision avoidance system - called a TCAS alert - kicked in and issued an audible alarm – "Traffic! Traffic!"
The alarm system instructed the pilots to adjust their vertical speed and descend. The first officer complied and the small aircraft passed overhead. "The planes were 300 feet apart vertically and 1,500 feet apart horizontally," reported ABC News. "Rules dictate that at that phase in flight planes should maintain a distance of 1,000 feet vertically and three miles horizontally."
Flight 889 was able to continue on to Beijing without further incident.
The National Transportation Safety Board has begun an investigation into the near-collision.