Possible Causes of the Crash
The National Transportation Safety Board (NTSB) is working with Boeing, the Federal Aviation Administration, and the Korean Air and Accident Investigation Board to determine the exact cause of the crash. A typical NTSB crash investigation can take 12 to 18 months, but Chairperson Deborah Hersman has stated that she hopes to have the report completed earlier.
There is no indication that the weather played any part in the crash. The weather was fair and the aircraft was cleared for a visual approach. The tower may have requested that the pilots make a visual approach as a result of the airport's Instrument Landing System (ILS) not functioning at the time of the landing. NTSB’s Hersman addressed the issue by stating that because the jet was on a visual approach in excellent weather, "you don't need instruments to get into the airport" safely. There has been speculation however, that Korean pilots tend to be more comfortable with automated systems and less comfortable with visual approaches than their western counterparts. A recent Reuters story reported that a Korean government aviation official said manual flying was once common among Korean pilots, many of whom where former military pilots. But in an effort to improve safety after a 1997 Korean Air crash in Guam, pilots were encouraged to make more use of automated controls. Many Korean commercial pilots are former military, having gained much of their flying experience in highly automated aircraft. On the otherhand, commercial pilots who trained in the U.S. tend to have had an opportunity to hone their skills flying smaller, simpler planes with fewer automatic features.
Slow Approach Speed
The pilots allowed the jet's speed to slow below proper approach speed. Seven seconds before impact a voice is heard on the cockpit voice recorder called out "increase speed." The relief first officer occupied the cockpit jump seat told NTSB investigators that he was warning them their speed was too slow as they approached the runway. Four seconds before impact the stall warning stick shaker rattles into audible action. 1.5 seconds before impact the pilots attempted to initiate a go-around. At that point the airplane was descending too close to the ground to recover.
Last Second Abort Attempt
According to former TWA pilot Barry Schiff, once the airplane as the plane nears its destination and goes below an altitude of 500 feet, “target airspeed on final approach must be established and stabilized; power required for the descent must be established and stabilized; the required rate of descent must be established and stabilized; and the airplane must be on the desired descent profile and stabilized. If any of these variables becomes unstabilized or allowed to vary significantly, the pilot is required to abandon the approach and begin anew.”
On a typical Boeing 777 landing, flying at an appropriate landing speed of 132 knots, the plane will descend to the benchmark of 500 feet about 35 to 42 seconds before landing. It is unknown at this point why the Asiana 214 pilot did not attempt to initiate an abort landing until several seconds before impact.
Aircraft Equipment or Systems Failure
From initial NTSB reports, there was no indication of any problem, mechanical or otherwise, with no distress calls or other problem reports during the flight except for the final few seconds. The NTSB is investigating whether a failure in the mechanics or in the crew's use of the aircraft's autothrottle system could have occurred. The NTSB reports that the auto throttle was programmed to be in the “Vertical Speed mode,” one of the 3 available modes. Typically, the Vertical Speed mode is used for step down descents during an earlier part of the approach process. The most preferred mode for final approach is known as the “Vertical Navigation with Speed Intervention mode.” It is not yet known why the pilot chose a less common mode for the final approach. Also, the autothrottle control was found to be in the "armed" position during documentation of cockpit levers and switches, differing from both the "on" and "off" positions, and the flying pilot's flight director was deactivated whereas the instructor pilot's was activated. “Armed” means that the auto throttle is available to be engaged, but is not necessarily active. Thorough understanding of each of the modes of the autothrottle, as well as understanding its armed and automatic processes and limitations is critical during final descent. The pilot must also be prepared to land the plane manually in case of any equipment malfunction or confusion. The NTSB will attempt to understand the pilots actions in respect to use of the autothrottle and their ability to land the plane without use of the autothrottle.
The flying pilot was undergoing training and had never landed a Boeing 777 plane at SFO. He only had 43 hours in the Boeing 777. Likewise, Flight 214 was the training pilot’s first flight as an instructor and he had never overseen a trainee during a landing. The NTSB will look at whether the training exercise distracted the pilots from performing their duties. Since the crash, Asiana has already announced that they will enhance the training program for pilots looking to fly new aircraft. The new measures will include enhancing training for visual approach and automated flight and conducting flight inspection on airports which are "vulnerable to safety."
One of the pilots reported being temporarily blinded by a bright light on approach at about 500 feet. There was little information regarding that claim, and Chairperson Hersman discounted the idea that the light was from a potentially dangerous laser. The crew was engaged in a training exercise. The NTSB will look to see whether the crew became so distracted during the approach that they lost awareness of their airspeed. It is unknown if any of the pilots were engaged with personal electronic devices such as cell phones or iPads during the approach. According to a New York Times story, one crash in which cellphone interference with airplane navigation was cited as a possible factor involved a charter in Christchurch, New Zealand, in 2003. Eight people died when the plane flew into the ground short of the runway. In the New Zealand crash, the pilot had called home, and the call remained connected for the last three minutes of the flight. In the final report, the New Zealand Transport Accident Investigation Commission stated, “The pilot’s own cellphone might have caused erroneous indications” on a navigational aid.” Not to mention the possibility of the pilot being distracted at one of the most critical parts of the flight.
Potential Language Barriers
According to the NTSB, the pilots were speaking both English and Korean in the cockpit. We assume that communication with SFO air traffic controllers was in English and the Korean communication that was recorded would have been between the Korean pilots. Additionally, it is unknown if the post-crash NTSB interviews of the pilots were conducted in English, Korean or with the aid of an interpreter. It would be part of the NTSB investigation to conclude if language differences played any role in delaying action or misinterpreting directives during the approach.
The pilots were at the end of a long transoceanic flight. The NTSB will look at how fatigue played a role in the flight crew's mistakes.
Construction at the Airport
According to the NTSB, a component of the airport's Instrument Landing System (ILS) that tracks the glide path of incoming airplanes was not working at the time of the crash.
The computerized system calculates a plane's path of descent and sends the information to pilots in real-time. The NTSB will investigate how the runway markings and the absence of the instrument glide slope contributed to the accident.
The investigation will examine the crashworthiness of the airplane. In particular it will examine the failure of some of the emergency slides to properly deploy. Two of the emergency slides may have actually deployed inside of the aircraft. Some passenger statements indicated that one of the malfunctioning slides may have temporarily trapped a flight attendant.