U.S. investigators have a running start as they examine the factors that may have caused Asiana 214, a Boeing 777 to crash. The early evidence is leaning toward pilot error, but let’s look at what we know.
The approach to runway 28 Left at San Francisco International airport presents some challenges, not unlike those at many other airports that are either built right on the ocean or next to it. Winds at these airports tend to be stronger and more unpredictable in terms of their gusts and direction. Bodies of water are also known to produce sudden updrafts and heavy fog. As of the latest briefing by investigators, it appears flying conditions were not a factor in the crash.
Instrument Landing System (ILS)
Like most major airports, San Francisco has an instrument landing system. The ILS is an electronic highway that guides modern jetliners down to the threshold of the runway at the proper angle and rate of descent. The most sophisticated ILS systems can auto-land an airliner like the Boeing 777 in zero visibility. Advance notice was provided to all pilots that the ILS system at San Francisco International airport was not working on Sunday. In good weather, this is not a problem because airline pilots land their aircraft using visual flight rules. That means pilots can eyeball their way down to the runway manually adjusting descent rate, pitch, roll and attitude. Even though the ILS was out at SFO, the runway had precision approach indicator lights that provide the pilots with visual cues as to how high or how low they are. Investigators say Asiana 214’s approach was unusually steep.
Touching down a heavy aircraft
After burning off most of its fuel on the flight from Shanghai and Seoul, the pilots would have had to make a calculation based on the weight of the Boeing 777 to determine their safest landing speed. The same math is used for take-off. Airliners must slow down enough to make a safe landing without going below stall speed. Stall has nothing to do with the engines. When an aircraft wing moves through the air too slowly or at too high an angle, the forces of lift that keep it flying can be dramatically reduced causing the wing to stall. This is one of the reasons flaps and slats are extended for landing. They allow a huge airplane to maneuver at slower speeds so the decent can be controlled and the pilots can set the plane down as gently as possible in the “touch down” zone. When a jet approaches the threshold of the runway it begins to pitch its nose up in what’s called a flare; not enough to climb, just enough to level off and slowly settle the aircraft on to its main landing gear under the wings. Knowing when to flare and when to cut the throttles are indicators of a pilot’s skill and experience, and why passengers applaud a good landing.
According to Boeing’s own specifications, the ideal landing speed for a 777 is 124 knots, depending on the aircraft’s weight. The last recorded airspeed for Asiana 214 prior to the crash showed a drop from 109 knots to 85 knots. Preliminary analysis of the flight data and cockpit voice recorders shows Asiana 214 approaching the runway below what should have been its target speed. The log also shows a final drop in altitude to 120 feet, followed by a climb of approximately 120 feet.
The attempt to gain altitude is supported by crash investigators who say the pilot tried to initiate a “go-around” just before impact. A go-around typically occurs when the pilot feels the approach is unstable or there is a runway incursion. I’ve seen go-around’s happen less than 50 feet above the runway. A go-around entails raising the nose to climb while pushing the throttles to full-power. Next, the landing gear is raised followed by the flaps in order to “clean up” the airplane and make it as aerodynamic as possible for the climb to a safe altitude where controllers can begin steering it back to the approach course. In modern jets, go-around’s can be triggered with the press of one button activating this sequence of events. But, even modern jet engines take a few seconds to spool up. Four seconds before hitting the ground, the stall warning sounded indicating the airliner was about to drop below the minimum speed required to stay in the air. About one-and-a-half seconds prior to impact, the pilots tried to raise the nose and abort the landing, but it was too late.
The pilot at the controls of Asiana 214 was a Captain who had logged more than 10,000 flying hours. However, he had only 43 hours at the controls of the Boeing 777. He was also making his first-ever landing at San Francisco International airport. The bigger the airplane, the more sluggish it is at lower air-speeds. Pilots know to avoid extreme or exaggerated corrections in their flight path. At about 300 feet above the ground, the Captain of a commercial airliner aircraft will call out the words “landing” or “continue”, indicating he believes the approach is stable for a safe landing.
While the factors outlined above point to pilot error, traditional wisdom in the aviation community tells us that even though the cause of a crash may seem obvious, it’s rarely the result of one single factor.
Ron Waksman is a former private pilot and aviation enthusiast who left journalism in 2001 to help launch a new Canadian airline with the Roots boys and Skyservice. Along with two of his sons, they are either talking about airplanes, watching them from the backyard deck or flying them on the computer. This fall, his eldest son begins flight school with the dream of becoming an airline pilot. Ron has what a former newsroom colleague calls “cockpit envy.”
WATCH: Investigators comb through the aftermath of the deadly plane crash at SFO