WASHINGTON — The pilots of the Asiana jumbo jet that crashed in San Francisco on July 6 were deeply confused about the plane's automated control systems, and that is a common problem among airline pilots, according to experts who testified Wednesday in a National Transportation Safety Board hearing on the crash.
"We do have an issue in aviation that needs to be dealt with," the chairwoman of the safety board, Deborah A.P. Hersman, told reporters during a break in the hearing.
The captain and the supervising pilot in the Asiana crash — in which a Boeing 777 hit a sea wall short of the runway, killing three passengers — said they thought a system that is used to control the plane's airspeed was running, although it was not. And all three pilots overlooked a prominent display that showed that their airspeed was too low.
According to documents released by the board, for 19 seconds leading up to the crash the pilots had a clear view of guidance lights on the field that indicated that they were flying too low, but they did not follow company procedure to break off the approach.
Government studies as far back as 1996 show a heavy reliance on automation that pilots often do not understand, witnesses said. One common problem is what they call "mode error," in which pilots become confused about what automated cockpit controls will do in a certain situation. The problem is akin to having trouble with the buttons on a remote control unit for a home entertainment system, but with greater consequences.
The plane's captain, Lee Kang Kuk, told investigators — although he was wrong — that he believed the protection system in the Boeing was similar to the one in the Airbus A320, which he had substantially more experience flying.
In the Boeing, the throttle levers — one for each of the two engines and located on a center pedestal between the captain and the first officer — will move as the automatic system manipulates the engines. In the Airbus they will not move even when the auto-throttle adjusts the engines' power.
Boeing's design leaves more discretion to the pilot and does not always ensure that the engines will maintain a minimum speed. Asiana ground school instructors warned the crews that the auto-throttle would be disabled when autopilot was being used by the crew to control the plane's descent to a certain altitude, according to one safety board document, but the lesson evidently did not stick.