飞机失事原因在于自动驾驶系统问题

根据Huffington Post的报道分析，旧金山飞机失事或者是因为自动控制机构出了问题，或者是自控系统操纵不当：

http://www.huffingtonpost.com/2013/07/09/san-francisco-plane-crash_n_3569670.html

SOUTH SAN FRANCISCO, Calif. — The pilots of Asiana Flight 214 relied on automated cockpit equipment to control the jetliner's speed as they landed at San Francisco airport, but realized too late they were flying too low and too slow before the aircraft crashed, investigators said Tuesday.

The new details were not conclusive about the cause of Saturday's crash, but they raised potential areas of focus: Was there a mistake made in setting the automatic speed control, did it malfunction or were the pilots not fully aware of what the plane was doing?

One of the most puzzling aspects of the crash has been why the wide-body Boeing 777 jet came in far too low and slow, clipping its landing gear and then its tail on a rocky seawall just short the runway. The crash killed two of the 307 people and injured scores of others, most not seriously.

Among those injured were two flight attendants in the back of the plane, who survived despite being thrown onto the runway when the plane slammed into the seawall and the tail broke off.

National Transportation Safety Board chairman Deborah Hersman said the autothrottle was set for 157 mph and the pilots assumed it was controlling the plane's airspeed. However, the autothrottle was only "armed" or ready for activation, she said.

Hersman said the pilot at the controls, identified by Korean authorities as Lee Gang-guk, was only about halfway through his training on the Boeing 777 and was landing that type of aircraft at the San Francisco airport for the first time ever. And the co-pilot, identified as Lee Jeong-Min, was on his first trip as a flight instructor.

Autothrottles typically have three settings – off, on and armed. An autothrottle that is armed but not on will remain at its previous speed, which was probably near idle, said Doug Moss, a pilot for a major U.S. airline and an aviation safety consultant in Torrance, Calif. Pilots will frequently shift to idle off and on when preparing to land in order to descend faster.

The pilot flying the plane had turned off his flight director, while the training captain had his flight director on, Hersman said. The flight director computes and displays the proper pitch and bank angles required in order for the aircraft to follow a selected path.

In most airliners, an autothrottle will not turn on if one flight director is off and one on because it has to work in harmony with the flight directors – both need to be either on or off, Moss said.