What happened
On July 6, 2013, an Asiana Airlines flight, operating a Boeing 777-20 andER with registration HL7742, was performing a visual approach to runway 28L at San Francisco International Airport. During the descent, the aircraft's airspeed decayed significantly, leading to a descent below the visual glidepath. The aircraft ultimately struck a seawall near the airport, resulting in the destruction of the plane. The accident caused 3 fatalities and left dozens of passengers and crew members with serious and minor injuries.
The investigation
The investigation focused on the flight crew's management of the approach and the aircraft's automated systems. Investigators examined the flight data, cockpit voice recordings, and the performance of the aircraft's autothrottle and flight director systems. A key area of scrutiny was the aircraft's ability to maintain airspeed and the effectiveness of the cockpit's alerting systems during a low-energy state. The investigation also looked into the training protocols for the flight crew and the adequacy of the airport's emergency response and communications.
Findings
Investigators identified several critical factors that led to the accident. A primary cause was the inadequacy of the B777's low airspeed alert, which functioned as a general caution rather than a high-priority warning. This lack of a distinct, urgent signal contributed to a delayed crew response. Additionally, the investigation found inconsistencies in the aircraft's airspeed protection functions, specifically that the autothrottle did not provide necessary protection in certain modes. The crew's failure to adhere to standard operating procedures regarding callouts and the use of flight directors during a visual approach also played a role in the uncontrolled descent.