The pilots of Asiana Flight 214 that crashed in San Francisco in July, as well as the airline, are raising the possibility that a device that controls the Boeing 777's speed may have malfunctioned.
National Transportation Safety Board chairman Deborah Hersman said early in the investigation that her experts had found no mechanical problems, but were investigating further.
One of the three pilots in the Asiana cockpit said he thought the plane's automatic throttle was maintaining speed as the plane descended to land, but later discovered it was not sending power to the engine.
The autothrottle controls engine power and speed. In the case of Flight 214, the plane was flying low and slow as the pilots attempted to land. The 777's landing gear struck a seawall just short of the runway.
The impact ripped off the back of the plane, tossed out three flight attendants and scattered pieces of the jet across the runway as it skidded to a stop.
The South Korean air carrier and the pilots involved have raised the possibility with investigators that the autothrottle disengaged on its own.
Two Chinese students were killed and 180 injured. A third student survived the crash but died after being run over by a fire truck.