The National Transportation Safety Board (NTSB) this week released a synopsis of their final report on last year’s crash of Asiana Airlines flight 214 at San Francisco International Airport (SFO). The report lists NTSB’s findings, identifies a probable cause, and makes 27 specific recommendations to Asiana, the FAA, and Boeing – among others. The crash was found to be pilot error – the result of a botched visual approach which culminated in the Boeing 777-200ER hitting a seawall and crashing onto the runway, killing three and seriously injuring dozens.
For anyone who has followed the crash investigation, there were no real surprises in the report. However, there are some interesting takeaways.
The NTSB also released this video which illustrates the events as the plane approached SFO’s runway 28L:
The probable cause statement is worded as such:
The National Transportation Safety Board determines that the probable cause of this accident was the flight crew’s mismanagement of the airplane’s descent during the visual approach, the pilot flying’s unintended deactivation of automatic airspeed control, the flight crew’s inadequate monitoring of airspeed, and the flight crew’s delayed execution of a go-around after they became aware that the airplane was below acceptable glidepath and airspeed tolerances. Contributing to the accident were; (1) the complexities of the autothrottle and autopilot flight director systems that were inadequately described in Boeing’s documentation and Asiana’s pilot training, which increased the likelihood of mode error; (2) the flight crew’s nonstandard communication and coordination regarding the use of the autothrottle and autopilot flight director systems; (3) the pilot flying’s inadequate training on the planning and executing of visual approaches; (4) the pilot monitoring/instructor pilot’s inadequate supervision of the pilot flying; and (5) flight crew fatigue which likely degraded their performance.
This statement recognizes that a mismanaged approach by the pilots was the fundamental cause of the accident. However, the report also highlights the complexity of the Boeing autopilot and autothrottle systems – and a lack of training about this complexity – as a contributing factor. The specific complexity in question is well known to 777 pilots and is informally called the “FLCH trap”.
This sequence of events occurs when the pilots initially set the aircraft’s autothrottle to maintain a given airspeed, but then set the autopilot to change the aircraft’s altitude using the Flight Level Change (FLCH) mode. Once the FLCH mode is selected, the autothrottle disengages, which can allow the plane to slow down below the set airspeed. The report goes on to makes several recommendations to Boeing: to update the aircraft operation manual to warn about this specific sequence of events, and to develop a context-specific airspeed warning system to ensure airspeed remains within limits for all phases of flight.
The FLCH trap notwithstanding, there is no doubt that the pilots of Asiana 214 should have been aware of the decreasing airspeed as the plane approached the runway. As anyone who has ever been student pilot can attest, one of the very first lessons of early flight training is flying a stabilized approach. This includes flying a consistent glideslope to the runway threshold and flying a constant airspeed. As the video above shows, both the airspeed and the glideslope varied wildly during the approach to runway 28L. As the aircraft approached the runway threshold, the pilots got further and further behind the curve, ultimately recognizing too late that the landing was unsalvageable.
One thing not identified as a contributing factor to the accident was the fact that the instrument landing system (ILS) glideslope was out of service at the time of the accident, which forced the pilots to manually fly the aircraft instead of configuring the plane to fly the approach automatically. The report rightly assumes that any qualified pilot should be capable of safely flying a manual approach without the use of automation and instrument landing systems. One of the recommendations made to Asiana was to decrease the reliance on automated approaches and to require pilots to regularly fly manual approaches.
The report also considers what happened to the plane during the crash itself. One area of interest are the slides/rafts on the 1R and 2R doors, which inflated inside the cabin, temporarily trapping two flight attendants in their seats. The slides inflated as a result of the forces of the crash, which far exceeded the design limits of the slides. The report recommends evaluating the need to change the load testing that slides are subject to.
Another area the report examines is the forces that were experienced by passengers during the crash. Many passengers received high thoracic spinal injuries as a result of lateral forces. The report recommends additional research into the injury mechanism experienced by these passengers, which may potentially result in new regulations for seat protection to mitigate against this kind of injury.
Finally, the report addresses the response by airport personnel following the crash. One of the three fatalities was as a direct result of a passenger being struck by a fire truck responding. This passenger had been ejected from the aircraft during the crash, was lying on the ground, and was not seen by responding firefighters. The report recommends that the aircraft rescue and firefighting working group work to establish best practices and training to avoid similar events in the future. Interestingly enough, both of the passengers that were ejected from the plane and perished were not wearing their seat belts.
Given the horrible nature of the crash, it is remarkable that more people didn’t lose their life. Modern air travel is among the safest transportation methods available; hopefully, the conclusions and recommendations from this incident can help make flying even safer.
The full report is available on the NTSB website.