WHY AIRSPEED IS IMPORTANT
Federal safety investigators say the Asiana Airlines Boeing 777 that crashed at San Francisco International Airport had slowed significantly below the target landing speed of 158 mph well before it reached the runway threshold. An attempt in the last seconds of flight to increase speed came too late. Here’s why an airplane’s air speed is so important:
• For an airplane to fly, its wings must generate lift to overcome the craft’s own weight, which is the force of gravity, and drag, which is the air’s resistance to the movement of the plane.
• The thrust of jet engines accomplishes this by pushing an aircraft forward and causing air to flow over and under the wings.
• Air speed is critical to keeping air flowing at rates specific to each type of aircraft in order to allow the wings to generate the lifting force.
• If the airplane’s air speed is too slow, the wings will stop generating sufficient lift and the craft will fall. An aircraft does not have to stop moving forward for it to lose lift.
Two flight attendants in the back of Asiana Airlines Flight 214 survived despite being thrown onto the runway when the plane slammed into a seawall and lost its tail during a crash landing at San Francisco’s airport, the head of the National Transportation Safety Board said Tuesday.
Chairwoman Deborah Hersman also revealed that the pilots told investigators they were relying on automated cockpit equipment to control their speed during final approach, which prompts questions about whether a mistake was made in programming the “autothrottle” or if the equipment malfunctioned.
The plane crashed when it came in too low and slow for landing. Hersman said the pilot at the controls was only about halfway through his training on the Boeing 777 and was landing that type of aircraft at the San Francisco airport for the first time ever. And the co-pilot was on his first trip as a flight instructor.
Saturday’s crash killed two people but remarkably 305 others survived, most with little or no physical injuries. A final determination on the cause of the crash is months away and Hersman cautioned against drawing any conclusions based on the information revealed so far.
Audio recordings show pilots tried to correct the plane’s speed and elevation only until seconds before hitting the seawall at the end of the runway, a calamitous impact that sent the fuselage bouncing and skidding across the airfield.
Here is what is known: Seven seconds before impact, someone in the cockpit asked for more speed after apparently noticing that the jet was flying far slower than its recommended landing speed. A few seconds later, the yoke began to vibrate violently, an automatic warning telling the pilot the plane is losing lift and in imminent danger of an aerodynamic stall. One and a half seconds before impact came a command to abort the landing.
The plane’s airspeed has emerged as a key question mark in the investigation. All aircraft have minimum safe flying speeds that must be maintained or pilots risk a stall, which robs a plane of the lift it needs to stay airborne. Below those speeds, planes become unmaneuverable.
Because pilots, not the control tower, are responsible for the approach and landing, former NTSB Chairman James Hall said, the cockpit communications will be key to figuring out what went wrong.
“Good communication with the flight crew as well as the flight attendants is something I’m sure they’re going to look at closely with this event,” he said Tuesday. “Who was making decisions?”
Hall was on the transportation board when a Korean Airlines Boeing 747 crashed in Guam in 1997, an accident investigators blamed in part on an authoritarian cockpit culture that made newer pilots reluctant to challenge captains.
Since then, the industry has adopted broad training and requirements for crew resource management, a communications system or philosophy airline pilots are taught in part so that pilots who not at the controls feel free to voice any safety concerns or correct any unsafe behavior, even if it means challenging a more senior pilot or saying something that might give offense.
If any of the Asiana pilots “saw something out of parameters for a safe landing,” they were obligated to speak up, said Cass Howell, an associate dean at the Embry-Riddle Aeronautical University in Daytona Beach, Fla.
“There are dozens and dozens of accidents that were preventable had someone been able to speak up when they should have, but they were reluctant to do so for any number of reasons, including looking stupid or offending the captain,” said Howell, a former Marine Corps pilot.
Investigators want to nail down exactly what all four Asiana pilots were doing at all times.
“We’re looking at what they were doing, and we want to understand why they were doing it,” Hersman said. “We want to understand what they knew and what they understood.”
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