Tuesday, March 30, 2010

Anatomy of a near disaster

The National Transportation Safety Board revealed today that a small plane and a commercial jetliner nearly collided over San Francisco on Saturday.

The NTSB release says:

At about 11:15 a.m. PDT on March 27, the crew of United Airlines Flight 889, a B777-222 (N216UA) destined for Beijing, China, carrying 251 passengers and a crew of 17,
was cleared to takeoff from San Francisco International Airport (SFO) on runway 28L and climb to an initial altitude of 3,000 feet. The first officer, who was flying the aircraft, reported that after the landing gear was retracted and the jet was at an altitude of about 1,100 feet, the tower controller reported traffic at his 1 o'clock position.

Immediately following the controller's advisory, the airplane's traffic collision avoidance system (TCAS) issued an audible alert of "TRAFFIC TRAFFIC." The pilots saw a light high wing airplane, an Aeronca 11AC (N9270E), in a hard left turn traveling from their 1 o'clock to 3 o'clock position. The first officer pushed the control column forward to level the airplane. Both crew members reported seeing only the underside of the Aeronca as it
passed to within an estimated 200-300 feet of the 777.

TCAS then issued an "ADJUST VERTICAL SPEED" alert, followed by a "DESCEND, DESCEND" alert. The first officer complied and the flight continued to Beijing without further incident.

The next time someone tells you that commercial airline pilots are glorified bus drivers, remind them of this scenario.

Given the estimated speed of both aircraft, disaster was literally just one second away.

It recalls one of the most tragic air disasters in the country, when a small plane collided with a jetliner over San Diego many years ago.


What happened? Almost certainly this will come down on the small airplane pilot and an air traffic controller. No airplane is allowed within about 5 miles of an airport like San Francisco (and also Minneapolis-St. Paul, where the no-fly zone extends to the ground near the High Bridge in St. Paul) unless they've been given clearance to enter and are under the guidance of a controller.

I've found the actual tape of the incident. In this tape, the tower controller in San Francisco clears the United flight for takeoff and tells the smaller plane to be looking for traffic. The smaller plane reports he has the Boeing 777 in site, and he is told to pass behind the jet. The controller then tells the pilot of the 777 that the small plane is "no factor."

She's not happy.

"That set off the TCAS," she says, which is the collision warning system.


  1. wow...unbelieveable. sounds like the FAA needs come down pretty hard on some folks here.

    thanks for sharing.

  2. Last year my wife and I were flying home from Florida at 9500' using flight following. The controller called traffic, "Nxxx, traffic 5 miles 10,000' a 737 opposite direction". I responded with traffic in sight and turned on all my lights (it was daytime). Apparently the 737 didn't see me and his TCAS was making noise, so he made a abrupt altitude change and started bitching at the controller. The controller responded that under VFR conditions, if one aircraft calls traffic in sight, 500' seperation is legal. The 737 passed directly over me. It was quite a sight. So even though the SF event made the news, since both aircraft were talking to the controller and the one aircraft saw the other, I'm not sure this is such a newsworthy event. Not desirable of course. If my encounter had been picked up by one of the websites that monitor ATC transmissions, maybe I could have made foxnews for no reason other than a faux near disaster.


  3. Keep in mind, though, it didn't become a news story because some news org uncovered it and blew it out of proportion. It became a news story because the NTSB made an initial review, then announced it was sending a team to SFO to investigate.