Boeing 777-200ER accident at San Francisco, California, 6 Jul 2013

Accident narrative

**Descent Below Visual Glidepath and Impact With Seawall: Asiana Airlines Flight 214**

On July 6, 2013, about 1128 Pacific daylight time, Asiana Airlines flight 214, a Boeing 777-200ER (Korean registration HL7742), struck a seawall while on approach to runway 28L at San Francisco International Airport in San Francisco, California. The airplane was destroyed by impact forces and a postcrash fire. Of the 291 passengers, 12 flight attendants, and 4 flight crewmembers aboard, three passengers were fatally injured. Forty passengers, eight flight attendants, and one flight crewmember received serious injuries. The other 248 passengers, four flight attendants, and three flight crewmembers received minor injuries or were not injured.

**The flight** Flight 214 was a regularly scheduled international passenger flight from Incheon International Airport in Seoul, Korea, operating under visual meteorological conditions on an instrument flight rules flight plan.

The pilot flying (PF) occupied the left seat. He was a trainee captain with 9,684 total flight hours, but only 33 hours in the Boeing 777. The flight was an operating experience training flight for the PF. The pilot monitoring (PM) occupied the right seat as the pilot-in-command. He had 12,307 total flight hours, including 3,208 hours in the 777, but this was his first flight as an instructor pilot. A relief first officer occupied the center jumpseat as an observer during the approach, while a relief captain remained in the cabin.

**Sequence of events** The flight was vectored for a visual approach to runway 28L. The instrument landing system (ILS) glideslope for the runway was out of service due to a construction project, but the localizer and precision approach path indicator (PAPI) were operational. The flight intercepted the final approach course about 14 nautical miles from the runway threshold at an altitude slightly above the desired 3° glidepath.

Air traffic control instructed the flight to maintain 180 knots until 5 nautical miles from the airport. The flight crew accepted the instruction but mismanaged the airplane's descent. When the airplane reached the 5-nautical-mile point, it was about 400 feet above the desired glidepath.

To increase the descent rate and capture the glidepath, the PF selected the flight level change speed (FLCH SPD) autopilot pitch mode. Because the airplane was below the mode control panel's selected altitude of 3,000 feet (set for a potential missed approach), the autoflight system initiated a climb. The PF disconnected the autopilot and manually moved the thrust levers to idle. This manual override caused the autothrottle to change to HOLD mode, a state in which the autothrottle does not control airspeed. The PF then pitched the airplane down to increase the descent rate. Neither the PF, the PM, nor the observer noted the autothrottle mode change to HOLD on the flight mode annunciator.

The PF commanded the flight directors to be turned off. The PM turned off the PF's flight director switch but left his own switch on, loosely following an informal Asiana practice. Because both switches were not off simultaneously, the autothrottle remained in HOLD mode rather than changing to speed mode.

As the airplane reached 500 feet above airport elevation—the point at which Asiana's procedures dictated the approach must be stabilized—the PAPI indicated the airplane was slightly above the desired glidepath. The airspeed had decreased to the proper approach speed of 137 knots. However, the thrust levers remained at idle, and the descent rate was about 1,200 feet per minute, well above the 700 feet per minute needed to maintain the glidepath. Despite these indications of an unstabilized approach, the flight crew did not initiate a go-around.

The airplane continued to descend below the desired glidepath, with the PAPI displaying three and then four red lights. The airspeed continued to decrease rapidly. About 200 feet, the flight crew became aware of the low airspeed and low path conditions. At 124 feet, with the airspeed at 114 knots, a quadruple chime master caution alert sounded.

At about 86 feet, the PM advanced the thrust levers and called "speed." The stick shaker activated at 39 feet as the airspeed reached its lowest point of 103 knots. The PM called "go around" at 29 feet, but the airplane did not have the performance capability to accomplish a go-around at that point.

At 1127:50, the main landing gear and the aft fuselage struck the seawall. The tail broke off at the aft pressure bulkhead. The airplane slid along the runway, lifted partially into the air, spun about 330°, and impacted the ground a final time before coming to a stop.

**What the investigation found** The National Transportation Safety Board found no evidence of any preimpact structural, engine, or system failures. The autothrottle and autopilot systems functioned as designed. The Board concluded that flight crew certification, medical conditions, and air traffic control handling were not factors in the accident. The Board also noted that although the ILS glideslope was out of service, its absence should not have precluded the successful completion of a visual approach.

The investigation determined that the PF had an inaccurate understanding of how the autopilot and autothrottle systems interacted to control airspeed in FLCH SPD mode, and how the autothrottle's automatic engagement feature operated. The autothrottle does not automatically engage or "wake up" to provide low-speed protection when in HOLD mode during a FLCH SPD descent. The Board found that the complexities of these systems were inadequately described in Boeing's documentation and Asiana's pilot training.

The Board found that Asiana's automation policy emphasized the full use of automation and did not encourage manual flight during line operations. The Board concluded that more manual flight would have improved the PF's proficiency, noting that he did not use pitch trim after disconnecting the autopilot, which would have provided a tactile cue that the airspeed was decaying.

The flight crew's inadequate monitoring of airspeed during the approach was attributed to expectancy, increased workload, fatigue, and automation reliance. The Board found that the crew was experiencing fatigue due to circadian disruption and fragmented sleep, which likely degraded their performance. The delayed execution of a go-around resulted from a combination of surprise, nonstandard communication, and role confusion between the PF and the PM.

During the impact sequence, forces far exceeded certification limits, causing the 1R and 2R slide/rafts to inflate inside the cabin, which injured and temporarily trapped two flight attendants. Six occupants were ejected from the airplane through the ruptured tail: four seriously injured flight attendants and two fatally injured passengers. The Board found that the ejected passengers were not wearing their seatbelts and would likely have survived if they had been restrained. The third fatally injured passenger was likely struck by a separating door during the final impact. The impact dynamics also threw occupants forward with a significant lateral force to the left, resulting in numerous left-sided rib fractures and high thoracic spinal injuries.

A postcrash fire initiated in the separated right engine and spread to the fuselage. Firefighters entered the burning cabin and extricated five passengers who were unable to self-evacuate. The Board noted that the airport's aircraft rescue and firefighting staffing level was instrumental in the successful interior fire attack and rescue.

However, the investigation identified issues with the emergency response. Communications difficulties occurred between mutual aid units and the airport due to a lack of radio interoperability and a breakdown in communications between dispatch centers. The airport's two emergency medical buses were not integrated into preparation drills and did not arrive at the accident site, delaying the delivery of backboards. High-reach extendable turrets on the firefighting vehicles were not used effectively initially due to a lack of guidance on when to pierce an airplane fuselage. Additionally, one of the ejected passengers was rolled over by two firefighting vehicles; the Board found that responders failed to verify their visual assessments of her condition before she was struck.

**Probable cause** The National Transportation Safety Board determined that the probable cause of this accident was the flight crew’s mismanagement of the airplane’s descent during the visual approach, the PF’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 PF’s inadequate training on the planning and execution of visual approaches; (4) the PM/instructor pilot’s inadequate supervision of the PF; and (5) flight crew fatigue, which likely degraded their performance.