A United Airlines B-777 jetliner came dangerously close to striking a small aircraft over San Francisco on Saturday, with the two planes coming an estimated 200 to 300 feet from each other, according to federal officials who launched an investigation into the incident Tuesday.
The planes came so close that a collision avoidance system sounded, and both pilots of the larger aircraft later reported they could only see the underside of the Cessna 182, a small, single engine aircraft.
The National Transportation Safety Board launched an investigation Tuesday, but said it was too early to suggest whether either aircraft, or air traffic controllers, or some person or factor was to blame.
The NTSB said it learned of the incident because of a three-week-old rule that requires airlines to report to the NTSB any time a plane takes action to avoid a collision because of an alert.
In this circumstance, United Airlines Flight 889 was departing San Francisco International Airport at about 11:15 a.m. Pacific time on a flight to Beijing, China. It was carrying 251 passengers and a crew of 17.
The first officer, who was flying the aircraft, reported the plane was at an altitude of about 1,100 feet when an air traffic controller reported a plane at his 1 o'clock position, the NTSB said. Immediately following the controller's warning, the planes traffic collision avoidance system - or TCAS - issued an audible warning.
The pilots saw the Cessna in a hard left turn traveling from their 1 o'clock to 3 o'clock position.
The first officer of the United plane pushed the control column forward to level the jetliner, and both pilots reported seeing the belly of the Cessna as it passed within 200 to 300 feet of them.
The NTSB said it is sending investigator Scott Dunham to San Francisco to begin the investigation.