FINDINGS
The following were not factors in the accident: flight crew certification and qualification; flight crew behavioral or medical conditions or the use of alcohol or drugs; airplane certification and maintenance; preimpact structural, engine, or system failures; or the air traffic controllers’ handling of the flight.
Although the instrument landing system glideslope was out of service, the lack of a glideslope should not have precluded the pilots’ successful completion of a visual approach.
The flight crew mismanaged the airplane’s vertical profile during the initial approach, which resulted in the airplane being well above the desired glidepath when it reached the 5 nautical mile point, and this increased the difficulty of achieving a stabilized approach.
The flight crew’s mismanagement of the airplane’s vertical profile during the initial approach led to a period of increased workload that reduced the pilot monitoring’s awareness of the pilot flying’s actions around the time of the unintended deactivation of automatic airspeed control.
About 200 ft, one or more flight crewmembers became aware of the low airspeed and low path conditions, but the flight crew did not initiate a go-around until the airplane was below 100 ft, at which point the airplane did not have the performance capability to accomplish a go-around.
The flight crew was experiencing fatigue, which likely degraded their performance during the approach.
Nonstandard communication and coordination between the pilot flying and the pilot monitoring when making selections on the mode control panel to control the autopilot flight director system (AFDS) and autothrottle (A/T) likely resulted, at least in part, from role confusion and subsequently degraded their awareness of AFDS and A/T modes.
Insufficient flight crew monitoring of airspeed indications during the approach likely resulted from expectancy, increased workload, fatigue, and automation reliance.
The delayed initiation of a go-around by the pilot flying and the pilot monitoring after they became aware of the airplane’s low path and airspeed likely resulted from a combination of surprise, nonstandard communication, and role confusion.
As a result of complexities in the 777 AFCS and inadequacies in related training and documentation, the pilot flying had an inaccurate understanding of how the autopilot flight director system and autothrottle interacted to control airspeed, which led to his inadvertent deactivation of automatic airspeed control.
If the autothrottle automatic engagement function (wakeup), or a system with similar functionality, had been available during the final approach, it would likely have activated and increased power about 20 seconds before impact, which may have prevented the accident.
A review of the design of the 777 automatic flight control system, with special attention given to the issues identified in this accident investigation and the issues identified by the Federal Aviation Administration and European Aviation Safety Agency during the 787 certification program, could yield insights about how to improve the intuitiveness of the 777 and 787 flight crew interfaces as well as those incorporated into future designs.
If the pilot monitoring had supervised a trainee pilot in operational service during his instructor training, he would likely have been better prepared to promptly intervene when needed to ensure effective management of the airplane’s flightpath.
If Asiana Airlines had not allowed an informal practice of keeping the pilot monitoring’s (PM) flight director (F/D) on during a visual approach, the PM would likely have switched off both F/Ds, which would have corrected the unintended deactivation of automatic airspeed control.
By encouraging flight crews to manually fly the airplane before the last 1,000 ft of the approach, Asiana Airlines would improve its pilots’ abilities to cope with maneuvering changes commonly experienced at major airports and would allow them to be more proficient in establishing stabilized approaches under demanding conditions; in this accident, the pilot flying may have better used pitch trim, recognized that the airspeed was decaying, and taken the appropriate corrective action of adding power.
A context-dependent low energy alert would help pilots successfully recover from unexpected low-energy situations like the situation encountered by the accident pilots.
The flight attendants acted appropriately when they initiated an emergency evacuation upon determining there was a fire outside door 2R. Further, the delay of about 90 seconds in initiating an evacuation was likely due partly to the pilot monitoring’s command not to begin an immediate evacuation, as well as disorientation and confusion.
Passengers 41B and 41E were unrestrained for landing and ejected through the ruptured tail of the airplane at different times during the impact sequence. It is likely that these passengers would have remained in the cabin and survived if they had been wearing their seatbelts.
Passenger 42A was likely restrained for landing, and the severity of her injuries was likely due to being struck by door 4L when it separated during the airplane’s final impact.
The dynamics of the impact sequence in this accident were such that occupants were thrown forward and experienced a significant lateral force to the left, which resulted in serious passenger injuries that included numerous left-sided rib fractures and one left-sided head injury.
The reasons for the high number of serious injuries to the high thoracic spine in this accident are poorly understood.
The release and inflation of the 1R and 2R slide/rafts inside the airplane cabin was a result of the catastrophic nature of the crash, which produced loads far exceeding design certification limits.
Clearer guidance is needed to resolve the concern among airport fire departments and individual firefighters that the potential risk of injuring airplane occupants while piercing aircraft structure with a skin-penetrating nozzle outweighs the potential benefit of an early and aggressive interior attack using this tool.
Medical buses were not effectively integrated into San Francisco International Airport’s monthly preparation drills, which played a part in their lack of use in the initial response to the accident and delayed the arrival of backboards to treat seriously injured passengers.
Guidance on task prioritization for responding ARFF personnel, that addresses the presence of seriously injured or deceased persons in the immediate vicinity of an accident airplane, is needed to minimize the risk of these persons being struck or rolled over by vehicles during emergency response operations.
The overall triage process in this mass casualty incident was effective with the exception of the failure of responders to verify their visual assessments of the condition of passenger 41E.
The San Francisco Fire Department’s aircraft rescue and firefighting staffing level was instrumental in the department’s ability to conduct a successful interior fire attack and successfully rescue five passengers who were unable to self-evacuate amid rapidly deteriorating cabin conditions.
Although no additional injuries or loss of life were attributed to the fire attack supervisor’s lack of aircraft rescue and firefighting (ARFF) knowledge and training, the decisions and assumptions he made demonstrate the potential strategic and tactical challenges associated with having non-ARFF trained personnel in positions of command at an airplane accident.
Although some of the communications difficulties encountered during the emergency response, including the lack of radio interoperability, have been remedied, others, such as the breakdown in communications between the airport and city dispatch centers, should be addressed.
The Alert 3 section of the San Francisco International Airport’s emergency procedures manual was not sufficiently robust to anticipate and prevent the problems that occurred in the accident response.
