Monday, August 05, 2013
The Things That Didn’t Happen To Flight 214
Just moments before Asiana Airlines Flight 214 was to land at the San Francisco International Airport on July 6, some passengers noticed that backdraft from the jet engines was kicking up seawater. This usually doesn’t happen on normal approaches to Runway 28L, which extends from just behind a seawall that faces San Francisco Bay onto land. A few seconds later, the main landing gear hit the seawall and sheared off. After that impact, both engines and the tail section came off, carrying some passengers and crew with it. The main fuselage slammed into the runway and spun almost completely around before grinding to a halt.
Flight attendants sprang into action, assisting passengers who needed help in exiting the aircraft. One injured girl was pulled from the plane by a first responder, only to be covered in firefighting foam from arriving fire trucks. Sadly, another emergency vehicle’s driver failed to see her underneath the foam, and she was struck and killed. Another passenger died at the scene and a third passed away a few days later from injuries. All of the other 304 people aboard survived, including all the pilots and crew, although some sustained serious injuries. After the plane was evacuated, a fire from an oil leak demolished much of the fuselage, but without injuring anyone.
Any fatal accident involving air travel is a tragedy—usually an avoidable one. But this accident could have been much worse, and that fact carries with it some implicit good news.
For one thing, the Boeing 777 involved is a model that was introduced in 1995, and this 2013 accident is the first one involving loss of passenger lives in a flight-related accident. Although fatal accidents have occurred earlier, they involved refueling or other ground-based situations. This is an outstanding safety record compared to planes developed during the earlier years of aviation.
Another fact worth noting is that the landing gear was purposely designed to break away under a sufficiently large impact, rather than staying attached to cause a destructive nosedive. We are familiar with breakaway traffic signs on highways, but I wasn’t aware until now that the same principle has been designed into landing gear.
Finally, the fact that the fuselage endured the abuse of skidding thousands of feet down the runway sans landing gear and kept the remaining fuel from catching fire, staying together long enough for everyone to escape, is a testimonial to its structural engineering. I am no mechanical engineer, but somebody did something right to make a fuselage that would hang in there during such a trial.
There are things that no airframe can endure, of course. If the plane had encountered a large immovable object, for example, the outcome might have been quite different. A similar accident in some ways to the Asiana Airlines crash took place on August 2, 1985. A Delta Airlines Lockheed L-1011 with 163 people on board was caught in a microburst and windshear during a thunderstorm at the Dallas-Fort Worth Airport during its final landing approach. The sudden loss of airspeed and accompanying downdraft forced the plane to the ground north of the runway, where it skidded into some giant water tanks and exploded. Only 26 people survived. Windshear detectors have since been installed at many airports, and pilots are much more aware of the dangers of such conditions, so the cause of that particular crash is much less likely to occur these days.
The cause of the Asiana crash is still under investigation, but attention has been focused on the flight crew, which consisted of three captains and a first officer. The man actually flying the plane at the time of the crash had less than fifty hours’ experience on 777s, and was being instructed by the pilot in command, who occupied the co-pilot’s seat at the time. The runway’s instrument landing system (ILS) vertical glide slope was out of service and a notice had been issued to that effect. This made it impossible to execute an ILS landing to the runway. Records indicate that the various automated landing-assistance systems were manipulated during the approach, and it may not have been clear to the flight crew that their approach was too low and slow until it was too late to do anything about it. The laws of inertia are always in force, and a lot of advance planning has to be done to bring a huge heavy object like a 777 in contact with the ground safely. Although final conclusions will have to await the completion of the ongoing investigations, it appears that pilot error may be at the bottom of this accident.
As long as human pilots fly planes, we will always have to contend with the possibility of pilot error. But in general, air travel is safer now than it has ever been, in terms of fatalities per passenger-mile flown. Even the absolute numbers of fatalities per year, which obviously stood at zero until the invention of the airplane, continues a downward trend that began in the 1970s, and is the lowest since about 1954. And the total number of passenger-miles flown in 1950 was only about 2% of what it was in 1990.
The Asiana crash may have stemmed from confusion about who was in charge—the autopilot mechanisms or the real pilot. But for the vast majority of planes and flights, the amazing system of man and machine called air travel operates efficiently, economically, and with a safety record that was unimaginable in the early days of flight.
Sources: I referred to the Wikipedia articles on “Asiana Airlines Flight 214,” “Delta Airlines Flight 191,” “USAirways Flight 1549,” and “Aviation safety.” I also obtained statistics on air travel safety from a paper by Prof. Dan Bogart of UC Irvine which can be found at http://www.socsci.uci.edu/~dbogart/transport_momentusBogart_6.11.12.pdf.