The National Transportation Safety Board (NTSB) this weekÂ released a synopsis of their final report on last yearâ€™s crash of Asiana Airlines flight 214 at San Francisco International Airport (SFO). Â The report lists NTSBâ€™s findings, identifies a probable cause, and makesÂ 27 specific recommendations to Asiana, the FAA, and BoeingÂ -Â among others. Â The crash was found to be pilot error – the result of a botched visual approach which culminatedÂ 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 crewâ€™s mismanagement of the airplaneâ€™s descent during the visual approach, the pilot flyingâ€™s unintended deactivation of automatic airspeed control, the flight crewâ€™s inadequate monitoring of airspeed, and the flight crewâ€™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 Boeingâ€™s documentation and Asianaâ€™s pilot training, which increased the likelihood of mode error; (2) the flight crewâ€™s nonstandard communication and coordination regarding the use of the autothrottle and autopilot flight director systems; (3) the pilot flyingâ€™s inadequate training on the planning and executing of visual approaches; (4) the pilot monitoring/instructor pilotâ€™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 highlightsÂ the complexity of the Boeing autopilot and autothrottle systems – and a lack of training about this complexity – as a contributing factor. Â TheÂ specific complexity in questionÂ is well known to 777 pilots and is informally calledÂ the “FLCH trap”.
This sequence of events occursÂ whenÂ 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. Â Once the FLCH mode is selected, the autothrottle disengages, which canÂ allow the plane to slow down below the set airspeed. Â The report goes on to makes severalÂ recommendations to Boeing: to update the aircraft operationÂ 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. Â As anyone who has ever been student pilot can attest, one of the very firstÂ lessons of early flight training is flying a stabilized approach. Â This includes flying a consistentÂ glideslope to the runway threshold and flying a constant airspeed. Â As the video above shows, bothÂ the airspeed andÂ the glideslope varied wildlyÂ during the approach to runway 28L. Â 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.
OneÂ thing not identifiedÂ 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. Â The report rightly assumes that any qualified pilot should be capable of safely flying a manual approach without the useÂ of automation and instrument landing systems. Â One of the recommendations made to Asiana was to decrease the reliance on automated approaches and to require pilots to regularlyÂ fly manual approaches.
The report alsoÂ considersÂ what happened to the plane during the crash itself. Â One area of interest areÂ the slides/rafts on the 1R and 2R doors, which inflated inside the cabin, temporarilyÂ trapping two flight attendants in their seats. Â The slides inflated as a result of the forces of the crash, which far exceeded the design limits of the slides. Â 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. Â Many passengersÂ received high thoracic spinal injuries as a result of lateral forces. Â 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. Â One of the three fatalities was as a direct result of a passenger being struck by a fire truck responding. Â This passenger had been ejected from the aircraft during the crash, was lying on the ground, and was not seen by responding firefighters. Â 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. Â 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. Â Modern air travel is among the safestÂ 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.